Rx Micro

Question 1

Patient presents with pseudomembranous colitis (fever, abdominal cramp, non - bloody diarrhea) after treatment of cellulitis with broad spectrum abx (clindamycin or ampicillin or fluoroquinolones)

• What is first line treatment mechanism for pt condition?

**What organism caused the pseudomembranous colitis? (Virulence factor)

Answer 1

1. Oral VANCOMYCIN - sever C.diff (first line tx used to be metronidazole)
   - inhibits cell wall peptidoglycan formation by binding D-ala D-ala
2. Fidaxomicin (first line for mild/moderate C.diff)
   - inhibit protein synthesis by inhibiting RNA polymerase

**Clostridium difficile caused pseudomembranous colitis by exotoxins A and B

Question 2

The following MoA correspond to what drugs

• 1 and 3 can treat C.diff
• 2 will cause C.diff

1. forming cytotoxic intermediates that damage bacterial DNA
2. inhibiting transpeptidase cross-linking and is associated with causing, not treating CDI
3. inhibiting protein synthesis by inhibiting the 30S subunit

Answer 2

1. Metronidazole
2. Ampicillin
3. Tigecycline

**1 and 3 are option in treatment of CDI (c.diff), however Oral vancomycin is first line of treatment

Question 3

35 y.o sexually active female with 1 week - mild fever, malaise, headache, non productive cough, CXR with bilateral infiltrate - ATYPICAL PNEUMONIA

1. What organism caused this?
2. What test will you order to support?

Answer 3

1. Mycoplasma pneumonia
   - has no cell wall
   - cell membrane contain cholesterol
2. Detection of an ELEVATED COLD AGGLUTININ TITER in the serum
   - this help differentiate viral atypical pneumonia from mycoplasma pneumonia
   - this test will cold agglutinins which are antibodies that cause RBCs to clump together at cold temperatures (half of patients with mycoplasma pneumonia)

Question 4

What test will you order for the following.

1. Diagnose systemic disease line Granulomatosis with polyangiitis
2. Diagnose HIV infection
3. Diagnose syphilis
4. Confirm diagnosis of HIV

Answer 4

1. Detection of c-ANCA in serum
2. Enzyme-linked immunosorbent assay to detect p24 antigen
3. Fluorescent treponemal antibody absorption test
4. Western blot to detect antibodies to viral proteins

Question 5

Patient with HIV for 1 year

• fever, night sweat, weight loss
• CD4 count is less than 50
• She is on Bactrium but not complaint with azithromycin

Which disease is most likely cause of condition

Answer 5

MAI - Disseminated Mycobacterium avium-intracellulare

• manifest as severe systemic illness in immunocompromised pts when CD4 count is less than 50

Question 6

MAI/MAC (disseminated mycobacterium avium intracellular) occur in HIV pt when CD4 count is less than 50

Identify other diseases with HIV pts

1. can occur when the CD4+ count is less than 400/mm³ or earlier. Infection typically presents with oral or genital ulcers.
2. can manifest when the CD4+ count is less than 400/mm³ or earlier. It is characterized by a painful collection of vesicles in a dermatomal pattern.
3. can occur when the CD4+ count is less than 500/mm³. It manifests with white patches and plaques on the oral mucosa.
4. is a common opportunistic infection when the CD4+ is less than 200 cells/mm³. It commonly manifests with fever, malaise, dyspnea on exertion, hypoxia, and a nonproductive cough.
5. may occur when a patient’s CD4+ count is less than 100 cells/mm³. It most commonly manifests with focal neurologic deficits, and a CT scan will show multiple ring-enhancing lesions.

Answer 6

1. Herpes simplex virus infection
2. Herpes zoster infection
3. Oral thrush
4. Pneumocystis pneumonia
5. A Toxoplasma brain abscess

Question 7

12 year old boy with sickle cell diease presents with;

• severe pain in right humerus
• radiograph show lytic changes and periosteum elevation in middle and distal humeral shaft

1. What does this indicate?
2. What is most likely pathogen for pt condition

**what are other common pathogens ?

Answer 7

1. OSTEOMYELITIS
2. SALMONELLA
   - most common cause of osteomyelitis in patients with sickle cell disease

• *Other common pathogens that cause osteomyelitis in sickle cell pt
• E. Coli
• Staph aureus

Question 8

A child with immunosuppressive disease (due to adenosine deaminase deficiency) comes for vaccination

1. What vaccine should you give?
2. Which shouldn’t you give

Answer 8

1. KILLED/INACTIVATED vaccine
   - Salk polio
   * Induce only humoral immunity with no ability to replicate
2. DO NOT give LIVE attenuated vaccines; dangerous for immunosuppressed pt
   - Sabin polio (oral)
   - influenza
   - MMR
   - Rotavirus
   - Typhoid (oral)
   - smallpox
   - varicella
   - yellow fever
   - zoster

Question 9

43 year old man just returned from trip in Great Lakes

• flu like symptoms, low grade fever, cough with productive purulent sputum and malaise.
• chest pain
• verucous lesion with irregular borders on right forearm
• radiograph show well circumcised osteopathic lesion in right forearm

*what will you see in biopsy?

Answer 9

Thick walled spherical YEAST producing single buds with a broad attachment base
(Pulmonary infection with extrapulmonary symptoms - skin/bone)

** BLASTOMYCOSIS (systemic mycoses) from inhaling dimorphic fungus - blastomyces dermatitidis; is endemic to the Midwest regions of the United States, including the Great Lakes. The skin is the most common site of extrapulmonary infection, followed by the bone. Biopsy specimens of affected areas show the characteristic yeast, which is thick walled and spherical, producing single buds with a broad base of attachment.

Question 10

A G1P0 27-year-old accountant at 26 weeks’ gestation visits her physician 5 weeks after returning from a trip to her grandfather’s home in rural India. She is jaundiced and complains of nausea, vomiting, fever, and abdominal pain. She denies any new sexual contacts and has never used recreational drugs. She has no significant medical history. Hepatomegaly is noted on examinatio
- High AST, ALT, total and direct bilirubin

** What is the genomic structure of the virus mostly likely to cause fulminant hepatic failure in this pregnant patient?

Answer 10

Single- stranded linear RNA

The hepatitis A (picornavirus) and hepatitis E (hepevirus) viruses both contain a single-stranded linear RNA genome and are transmitted by the fecal-oral route. Infection is often characterized by jaundice and systemic symptoms in adults and recovery occurs within a few months in immunocompetent hosts.
***HEPATITIS E is associated with fulminant hepatic failure in pregnant patients.

Question 11

A 5-year-old boy is brought to the emergency department because of a 2-day history of fever (38.3°C [101°F]), sore throat, hoarse voice, nasal congestion, and violent coughing (seal-like barking cough). The child’s mother reports that his cough has been worse at night and has failed to respond to home remedies. On auscultation, inspiratory stridor is heard. Between coughing spells, the child is noted to have intercostal retractions.
- CXR show steeple sign

** What is the RNA genome structure of the virus that is most likely causing this patient′s illness?

Answer 11

Single-stranded, negative- sense, linear, nonsegmented RNA

A “barking” cough, hoarse voice, inspiratory stridor, and a positive “steeple sign” on a chest x-ray are found in patients with CROUP. Croup is caused by the PARAINFLUENZA virus (paramyxoviridae - envelop and helical capsid), which is a single-stranded, negative-sense, linear, nonsegmented RNA virus.

• *3 circular RNA virus - dhey are ball (delta virus, arenavirus, Bunyavirus)
• all other RNA virus are linear

Question 12

A 19-year-old construction worker presents to the emergency department with a 12-hour history of a temperature of 39°C (102.2°F). His chief complaint is a fever, severe headache, and neck stiffness. On physical exam, passive flexion of the neck causes flexion at the hip. He states that because of his immigration status he has no previous knowledge of his medical records.

Which of the following symptoms would most likely be associated with this patient’s current condition?

Answer 12

Refractory hypotension, widespread maculopapular lesions

**NEISSERIA MENINGITIDIS is a gram-negative diplococcus that is a major cause of meningitis and sepsis. It can result in disseminated intravascular coagulation (DIC), SHOCK, and adrenal failure (Waterhouse-Friderichsen syndrome).

Question 13

A 27-year-old homeless man presents to the clinic because of a 5-day history of pain and swelling in his right upper arm. MRI of the area reveals diffuse soft tissue and bone inflammation. Bone biopsy is performed (see image - bone abcess with PMN leukocytes and degraded bone collagen). Blood culture speciation is pending, but preliminary results have grown out a gram-negative, oxidase-positive rod.

** Which of the following is a complete history of this patient most likely to reveal?

Answer 13

IV DRUG USE

Intravenous drug use is a major risk factor for osteomyelitis caused by Pseudomonas.

Question 14

A 12-year-old boy is brought to the pediatrician because of a 3-day history of watery, non-bloody, foul-smelling diarrhea. He remained afebrile during this period but has experienced some nausea, malaise, and bloating. His family recently returned from a vacation during which they spent a day in Tijuana, Mexico. The pediatrician suspects infection with Giardia lamblia.

Which of the following findings would confirm the pediatrician’s clinical diagnosis?

Answer 14

= Trophozoites in the stool

Infection with Giardia lamblia causes an acute nonbloody, watery, foul-smelling diarrhea. It is transmitted via the fecal-oral route in contaminated food or water. It occurs throughout the world, but is mostly related to places with poor sanitation. The easiest way to diagnose Giardia is by finding trophozoites in the stool.

Question 15

A 21-year-old woman comes to the clinic because of a painful ulcer on her lower lip for the past 3 days. On further questioning, she states that she has experienced identical symptoms in the past with painful vesicles organizing into ulcers over a 1–2-week period.

An image of the biopsy sample taken from the lesion is shown = multinucleated giant cell and intranuclear inclusions

**what other manifestation would you see?

Answer 15

Keratoconjunctivitis (acute onset of pain, blurry vision and ocular discharge - lead to corneal blindness)

Infection with herpes simplex virus type 1 (HSV-1) may cause herpes labialis (cold sores), which are recurrent ulcers localized on the lips. HSV-1 infection can also manifest as keratoconjunctivitis, temporal lobe encephalitis, or gingivostomatitis. Biopsy of an HSV lesion shows characteristic multinucleated giant cells and intranuclear inclusions.

Question 16

30-year-old missionary, who recently returned from a trip to South America, comes to the clinic with symptoms of high fever, headache, and back pain. He denies receiving any vaccinations before his travels

• high temp, BP 98/72, tachycardia, high RR
• tendernesss all 4 quadrant, enlarged liver and yellow pigmentation without the conjunctiva, vomiting dark colored blood
• positive test to reverse transcription polymerase chain test

**Which of following viruses is a member of same family as the one causes problems

Answer 16

Hepatitis C

YELLOW FEVER is a mosquito-borne viral illness caused by a flavivirus, a member of the Flaviridae family, which includes single-stranded, positive, linear RNA viruses. The Flaviviridae family also includes hepatitis C virus, Dengue, West Nile virus, St. Louis encephalitis, and Zika virus.

Question 17

12-year-old boy is brought to the emergency department by his mother after 3 days of fever and delirium. The patient reports weakness and a severe sore throat that makes him feel like he is gagging. His mother notes that 2 months earlier, their family took a trip where they went hiking, camping, and cave-exploring. The boy developed fever, chills, nausea, and lethargy shortly after returning home, but they did not seek medical attention at the time, and the symptoms subsided. Over the past 3 days, he has experienced decreased oral intake and rapid weight loss. On physical examination, the patient appears agitated and acutely ill. His mother reports that his routine immunizations are up to date. The emergency physician recommends immediate treatment.

What pathogen is most likely responsible for this patient’s condition?

Answer 17

Enveloped single stranded RNA virus

RABIES infection manifests early with a nonspecific prodrome, followed by a long incubation that slowly progresses to severe encephalitis with hydrophobia. The rabies virus is a member of the rhabdovirus viral family, which are single-stranded, enveloped, and helical.

Question 18

A mother brings her 12-year-old daughter to an outpatient clinic. The child complains of aching pain localized to the joints of the extremities. The mother recalls that her daughter was sick with a sore throat about a month ago but recovered completely without medical attention. The girl is admitted to the hospital for further examination and testing. A tissue biopsy specimen is obtained, and the findings are shown in the image = ASCHOFF NODULES (interstitial myocardial granulomas)

Based on the patient’s diagnosis, which of the following murmurs is most likely to develop in adulthood?

Answer 18

A Mid- diastolic murmur heard best at the apex (mitral valve stenosis)

RHEUMATIC HEART DISEASE, uncommon in the United States, occurs after pharyngeal infection with group A streptococci. Rheumatic heart disease affects high-pressure valves first: mitral, then aortic, and finally tricuspid valves.

Question 19

A 6-month-old girl with difficulty breathing is brought to the emergency department. Nasal flaring and suprasternal retractions are noted on arrival. The parents state that the child has been getting progressively sicker after developing a cough and rhinorrhea 3 days earlier. She has no past medical history.
Vital signs are: temperature 37.4°C (99.4°F), blood pressure 80/40 mm Hg, pulse 120/min, respiratory rate 36/min, and SpO2 90% on room air. Auscultation of the lungs reveals wheezes and rhonchi bilaterally. Intubation was required after nasal suctioning, and supplemental oxygen did not improve the patient’s SpO2.

Which of the following describes the most likely etiologic agent of the girl’s condition?

Answer 19

Enveloped RNA virus with a single-stranded, negative-sense, and non-segmented genome

Respiratory syncytial virus (RSV - PARAMYXOVIRIDAE) is a single-stranded, non-segmented, negative-sense, enveloped RNA virus and is the most common cause of BRONCHIOLITIS in children <1 year of age.

Question 20

A 43-year-old woman who has two adult children comes for evaluation because of a 1- to 2-week history of fatigue, constipation, and neck pain. Approximately 1 month ago, she had a short, flu-like illness from which she completely recovered. On examination her skin is cool; however, despite the warm weather, she is wearing several layers of clothing. Her deep tendon reflexes show delayed relaxation phases, and her thyroid gland is extremely tender to light palpation; no masses are noted. Laboratory studies show an elevated thyroid-stimulating hormone level and erythrocyte sedimentation rate.

Which of the following is the most likely diagnosis?

Answer 20

De Quervain thyroiditis aka granulomatous thyroiditis

De Quervain thyroiditis is a transient hypothyroidism seen after viral illnesses. It is characterized by an exquisitely tender thyroid gland, elevated erythrocyte sedimentation rate, and other manifestations of hypothyroidism, including fatigue, cold intolerance, cool skin, and decreased deep tendon reflexes.

Question 21

22-year-old man presents to the emergency department complaining of a spreading rash after several days of high fevers, severe headaches, and myalgia. He had recently returned from a Peace Corps trip to Rwanda. He first noticed the rash on his chest, but it has now spread to his legs and arms. His temperature is 38°C (100.4°F), pulse is 88/min, respiratory rate is 20/min, and blood pressure is 125/87 mm Hg. Physical examination reveals erythematous maculopapular eruptions on his chest, forearms, and thighs. A Weil-Felix reaction test is positive for OX-19, but negative for OX-2 and OX-K.

Which of the following is the most appropriate treatment?

Answer 21

Doxycycline

The rash of Rickettsia prowazekii, or epidemic typhus, characteristically begins centrally and spreads out; it is best treated with tetracyclines.

• *Classid triad of Rickettsia (gram negative bacteria) ; Headache, fever and rash
• *Weli-Felix reaction test confirms bacteria - non specific agglutination test that detect antirickettsial antibodies in a patients serum

Question 22

A 38-year-old man presents to the emergency department due to seizures that started earlier that day, as reported by his sister. He adds that his vision is also blurry. The patient says he has never traveled outside of the United States. Physical examination reveals several enlarged cervical lymph nodes as well as a right homonymous hemianopia. Review of his chart shows a CD4 count of 78 cells/μL from 2 months ago.

Which of the following is the most likely cause of this patient’s symptoms?

Answer 22

Toxoplasma gondii

Toxoplasmosis is a central nervous system infection of HIV patients (with CD4 <100 cells/μL) that leads to focal neurologic deficits and chorioretinitis. Toxoplasmosis has been reported as the most common opportunistic infection in HIV/AIDS in developed countries and is the most common cause of focal brain lesions, coma, and death. It commonly causes encephalitis in HIV-infected patients.

Question 23

78-year-old man who is HIV positive man comes to the physician because of a growing “bruise” on his left forearm. Upon further questioning, the man states that he was prescribed some medicine for HIV when he was first diagnosed at age 40 but stopped taking it after a few years. Inspection of the area reveals multiple purple macules and papules that are firm to palpation.

Which of the following diseases is in the same taxonomic family as the cause of this patient’s presenting symptoms?

Answer 23

Roseola infantum

Kaposi sarcoma is an AIDS-defining illness caused by HHV-8, which belongs to the herpesvirus family. Other members of the herpesvirus family are: herpes simplex virus-1 and herpes simplex virus-2 (oral and genital lesions), Epstein-Barr virus (mononucleosis and Burkitt lymphoma), cytomegalovirus (mononucleosis), roseola infantum (HHV-6), and varicella-zoster virus (chickenpox and shingles).

Question 24

An 8-year-old boy with a fever, cough, chills, and shortness of breath is brought to the pediatrician’s office. His mother reports that her son has had numerous respiratory infections over the past 3 years, as well as a history of foul-smelling stools that float. His vitals sign are: temperature 39.4°C (103°F), blood pressure 112 mmHg, pulse 90/min, and respiratory rate 30/min. He has an SpO2 of 92% on room air.
On physical examination, the patient looks small for his age. Expiratory crackles are heard bilaterally. Cardiovascular and abdominal exams are unremarkable. Microscopic analysis of the patient’s sputum culture =

** The toxin produced by the organism responsible for this patient’s symptoms has which of the following mechanisms of action?

Answer 24

ADP ribosylates and inhibits elongation factor 2

Pseudomonas aeruginosa is a common cause of repeated pneumonia in patients with cystic fibrosis and is known to produce exotoxin A, which ADP ribosylates and inhibits ribosomal elongation factor 2 in the host cell, thereby shutting down protein synthesis.

Question 25

A 32-year-old man with asthma is admitted to the hospital in status asthmaticus, and albuterol is administered continuously by means of a nebulizer. Four hours into his hospital course, this patient experiences acute respiratory failure; he is intubated and transferred to the intensive care unit. After he has been receiving mechanical ventilation for 96 hours, the physician notes that this patient requires more ventilatory support and has developed a fever and purulent tracheobronchial secretions. X-ray of the chest reveals a right lower lobe infiltrate. Tracheobronchial aspiration yields a sample that is sent to the laboratory for analysis.

Infection with which of the following organisms is most likely?

Answer 25

Pseudomonas aeruginosa

Sedative medications required for intubation can cause depression of native ciliary elevator function of natural respiration. This increases a patient’s susceptibility to certain respiratory pathogens and can lead to VAP.
*P. aeruginosa is the organism most commonly associated with VAP.

Question 26

A 78-year-old man who lives at an assisted living facility sees his physician after experiencing several days of productive cough, abdominal pain, and fever. He also reports several episodes of diarrhea. The patient’s vital signs are: temperature, 102°F (38.8°C); blood pressure, 119/80 mm Hg; heart rate, 89; and respiratory rate, 18. Physical examination reveals bronchial breath sounds in the right lung fields and rales in the left lung fields. Results of abdominal and cardiac examinations are normal. Laboratory test results are as follows: thrombocytopenia, elevated creatinine and blood urea nitrogen (BUN) levels, hyponatremia, and hypophosphatemia.

Gram staining of a sputum sample reveals large neutrophils but no organisms.

Which of the following will identify the organism that is most likely causing this patient’s condition?

Answer 26

Culture of the organism on buffered charcoal yeast extract agar

When Legionella pneumophila infection is suspected, the appropriate culture medium is buffered charcoal yeast extract agar with iron and cysteine in combination with urinary antigen testing. Typically, Gram staining reveals large neutrophils but no organisms.

Question 27

38-year-old man comes to the emergency department because of recurrent episodes of fevers, intense headaches, and weakness. The patient reports that the fevers happen every 24–48 hours but he has not been able to identify a clear pattern. He also mentions that he wakes up with his sheet soaked through some nights and attributes some of his “generalized weakness” to a lack of sleep during these episodes. His symptoms began approximately 1 week after he returned from an overseas trip. He denies any shortness of breath, unexpected weight loss, or gastrointestinal symptoms. His temperature is 39°C (102.2°F), heart rate is 86/min, respiratory rate is 16/min, blood pressure is 118/76 mm Hg, and oxygen saturation is 98% on room air. Physical examination reveals hepatosplenomegaly. Toward the end of the examination, he develops a generalized seizure. A T2-weighted FLAIR MRI of the brain is shown = diffuse cerebral edema

**what parasite

Answer 27

Plasmodium falciparum (cerebral malaria)

Four Plasmodium species may cause malaria, which presents with cyclic fevers, anemia, and hepatosplenomegaly. Of the Plasmodium species that cause malaria in humans, only P. falciparum has cerebral involvement.

Question 28

38-year-old woman, who is currently undergoing chemotherapy as treatment for nodular sclerosing Hodgkin lymphoma, comes to the physician reporting a 2-day history of vaginal burning and itching. She started chemotherapy 6 weeks ago and, apart from her present symptoms, has been tolerating it “pretty darn well.” She is not sexually active. Her temperature is 37.2°C (98.9°F), blood pressure is 134/82 mm Hg, pulse is 77, and respiratory rate is 17. On physical examination, the walls of the vagina and vulva are reddened and swollen, and copious amounts of white, thick discharge are seen throughout the vaginal canal. A sample of the discharge is taken and subsequently Gram stained. A photomicrograph of the Gram-staining result (1000× magnification) is shown in the image.

** Which of the following conditions is most likely to be seen in this patient?

Answer 28

Esophagitis

C. albicans is a yeast and common opportunistic pathogen. Vaginal itching with a whitish, curd-like discharge is suggestive of C. albicans vulvovaginitis. Candida infection can also cause esophagitis in immunocompromised patients

Question 29

An obese 43-year-old woman has been having abdominal pain and a fever. She noticed that her eyes started turning yellow 2 days ago. Physical examination reveals jaundice and right upper quadrant tenderness without rebound tenderness or guarding. Her liver and spleen cannot be palpated below the ribs. The patient’s history is significant for mild, intermittent epigastric pain after meals over the past several months.
Laboratory test results are: RBC, 4.1; Hb, 12.3; Hct, 36.1; WBC, 14,200/mm3 with 74% segmented neutrophils; platelet count, 359; serum lipase level, 78 U/L (normal range 0–160 U/L).

Which of the following is most likely responsible for this patient’s condition?

Answer 29

Bacterial cholangitis (bacterial infection of bile duct)

The presence of fever, jaundice, and upper right quadrant pain (CHARCOT TRIAD) in a patient should raise suspicion for cholangitis

Question 30

23-year-old man presents to the emergency department with bloody diarrhea, abdominal pain, and fever for one day. He denies any episodes of vomiting, recent illnesses, sick contacts, or a change in the frequency of bowel movements or urination. Temperature is 100.9°F (38.2°C), blood pressure is 121/80 mm Hg, pulse is 88/min, respiratory rate 16/min, and oxygen saturation is 98% on room air. Stool cultures grow an oxidase-negative, motile, gram-negative bacillus that grows as clear colonies on MacConkey agar at 37°C. When plated on Hektoen enteric agar, the colonies appear light green with black centers.

Which of the following is the most likely causative organism?

Answer 30

Salmonella enterica enteritidis

Common causes of bloody diarrhea include Salmonella, Shigella, E. coli, Campylobacter, and Yersinia. These pathogens can be differentiated by lab and culture results. Salmonella is the only producer of hydrogen sulfide, which can be detected on Hektoen agar culture (form black precipitate).

Question 31

A man who is sexually active with other men presents to the clinic with a report of perianal lesions. He says that the lesions are not painful, but there is some itchiness. The man says that he has not had them before. He reports that he has had eight sexual partners in the past 3 months and that he uses condoms “most of the time.” He denies any other symptoms including skin rash, other lesions, fevers, burning on urination, or swollen lymph nodes. He does report a history of sexually transmitted infections. The result of a rapid HIV test is positive.

Other screening test results are pending. The patient’s lesions resemble those shown in the image = multiple, white, hyperkeratotic, pedunculated verrucae clustered in the perianal region

Which of the following pathogens is most likely responsible for this patient’s condition?

Answer 31

Human papillomavirus type 6 (caused the GENITAL WARTS)

HPV types 6 and 11 are the most common causes of CONDYLOMATA ACUMINATA. These two types rarely transform into malignancy. Risk factors include unprotected sexual contact, immunocompromised status, and a history of smoking. HPV types 16 and 18 are more commonly associated with cervical dysplasia (flat genital warts).

Question 32

A 36-year-old man comes to the physician complaining of an aching back, high fever, and vomiting of dark material for the past week. The patient reports that he recently returned from an African safari in western Kenya and confirms that he was bitten by numerous mosquitoes. Physical examination reveals a febrile male in distress. He denies recent alcohol use. The patient’s temperature is 39°C (102.2°F), and he has a yellow tinge to the white of his eyes.

Biopsy of the liver would yield which of the following findings?

Answer 32

Councilman bodies

Councilman bodies are eosinophilic globules seen on liver biopsy indicative of the apoptosis of hepatocytes characteristic of YELLOW FEVER (flaviviridae). Yellow fever typically manifests with body aches, high fever, and dark vomitus.

Others

• Döhle bodies are found in neutrophils, typically during infections.
• Mallory bodies are found in alcoholic hepatitis.
• Negri bodies are associated with rabies virus and are found in the cytoplasm of infected neurons.
• Weibel-Palade bodies are normal components of vascular endothelium and store vWF and P-selectin.

Question 33

A 68-year-old man who smokes and is an alcoholic abruptly develops high fever, shakes, a severe headache, watery diarrhea, and abdominal and muscle pain. He presents with a dry, insignificant cough, but over the next few days he develops marked shortness of breath requiring assisted ventilation. X-ray findings of the chest are shown (SEVERE PNEUMONIA), and the results of a basic metabolic panel are listed. Culture of bronchoalveolar lavage fluid demonstrates a bacillary pathogen.

What is the most likely causative organism?

Answer 33

Legionella pneumophila

Legionella pneumophila causes pneumonia in older patients; risk factors include a history of alcoholism, tobacco use, diabetes, chronic illness, or immunosuppression. Diagnosis can be confirmed with lower respiratory secretions cultured on buffered charcoal yeast extract and a urine antigen test. It is often acquired from contaminated water and is associated with WATERY DIARRHEA and HYPONATREMIA.

OTHERS;
Listeria monocytogenes and Klebsiella pneumoniae are not notable causes of pneumonia. Although Staphylococcus aureus and Streptococcus pneumoniae are common causes of pneumonia, the patient’s lab results and the overall clinical picture point to Legionella as the more likely culprit.

Question 34

A healthy 8-year-old boy climbs over a fence into his neighbor’s backyard to retrieve a soccer ball. While searching for the ball, he is attacked and bitten by the neighbor’s dog. He is rescued by a nearby neighbor, who brings him home to his parents. The wound is deep, and his parents clean it with soap and water. Ten hours later, the wound is purulent and inflamed, so his parents take him to the emergency department. The purulent exudate is cultured, and the results show growth of gram-negative coccobacilli.

Which of the following microorganisms is the most likely cause of infection in this patient?

Answer 34

Pasteurella multocida

The most common cause of cellulitis in a patient after a cat or dog bite is Pasteurella multocida, typically a gram-negative coccobacillus (with some variability in morphology).

OTHERS

• Bartonella henselae is a gram-negative rod that is usually associated with cat scratches and most often causes lymphadenitis in young children.
• Brucella canis, a gram-negative rod that is normally found in dogs, can cause fever, malaise, and hepatosplenomegaly in humans, but not usually purulence.
• Eikenella corrodens is a gram-negative, facultative, anaerobic bacillus found in the human oral cavity. It is one of the HACEK organisms involved in endocarditis.
• Francisella tularensis is a gram-negative rod acquired via contact with infected rabbit tissue.

Question 35

36-year-old man comes to the emergency department because of an acute and sudden onset of unremitting vomiting that began the previous evening. He also reports nausea, abdominal pain, and diarrhea and denies fever or blood in the vomit or stool. He has had no recent sick contacts. His medical history reveals essential hypertension treated with amlodipine, and upper respiratory symptoms, runny nose, and congestion approximately 3 weeks ago. He denies any recent travel or changes in health.
The patient’s last full meal was lunch with his co-workers and consisted of chicken with vegetables, fried rice, and cheesecake. He remembers eating leftovers at dinnertime that day.

His temperature is 98.7°F (37°C), blood pressure is 110/78 mm Hg, pulse is 92/min, and respiratory rate is 14/min.

On physical examination, the patient appears well-nourished and in no acute distress. There is no erythema or exudate of the pharynx. Heart sounds are regular and lungs are clear on auscultation. There is mild, diffuse tenderness on palpation of the abdomen and bowel sounds are hyperactive.

Which of the following is the most appropriate next step in the management of this patient’s illness?

Answer 35

Prescribe no antibiotic therapy and provide supportive procedures

Bacillus cereus, often found in reheated rice, produces an exotoxin that can rapidly cause abdominal pain, vomiting, and nonbloody diarrhea. It is treated with supportive care. Antibiotics are not effective against this pathogen.

Others

• Prescribing an antibiotic that inhibits the 30S ribosome, for example, a tetracycline or aminoglycoside might be useful for foodborne Shigella infection.
• Metronidazole, an antibiotic that induces DNA damage in anaerobes, is used to treat Helicobacter pylori.
• Macrolides, such as clarithromycin and erythromycin inhibit protein translation with the 50S ribosome; these drugs might be used to treat severe cases of Campylobacter jejuni enterocolitis.
• Fluoroquinolones inhibit topoisomerase II and can be used to treat severe Shigella infection.
• Admitting the patient for observation and recommending stool analysis and blood cultures before proceeding with treatment suggest a more severe infection that would require more elevated care or further investigation.

Question 36

70-year-old woman comes to the emergency department because of left knee pain 2 weeks after undergoing arthroplasty of the knee. Her temperature is 100.2°F (37.8°C), blood pressure is 130/85 mm Hg, pulse is 90/min, and respiratory rate is 19/min. Physical examination discloses swelling, erythema, and decreased range of motion in the left knee. Fluid from the joint is aspirated and sent for Gram stain and culture.

Which of the following is most likely to be observed upon laboratory examination of the joint fluid?

Answer 36

Gram-positive, catalase-positive cocci

Staphylococcus aureus and Staphylococcus epidermidis are gram-positive, catalase-positive cocci that are likely to cause septic arthritis after joint replacement surgery.

Others

• A gram-negative lactose-fermenting bacilli describes E. coli which is usually found in UTIs.
• Gram negative non-lactose fermenting bacilli describes Salmonella which would present with bloody diarrhea and GI symptoms.
• Additionally, gram-negative glucose fermenting cocci would be descriptive of Neisseria which is found in cases of meningitis and sexually transmitted diseases.
• Gram-positive catalase negative cocci describes Streptococcus species, which is often found in diseases such as pharyngitis and scarlet fever.

Question 37

A 43-year-old man who is HIV-positive presents to the emergency department complaining of vision problems over the past 2 days. Neurologic examination reveals problems with speech, memory, and coordination. CD4 cell count is 24 cells/mL. He is admitted to the hospital, but his symptoms rapidly worsen and he dies 3 weeks after admission. During his hospitalization, a 3D FLAIR MRI revealed nonenhancing areas of demyelination.

Which of the following is the most likely cause of death in this patient?

Answer 37

JC virus

JC virus is an infection of HIV patients that results in PML (progressive multifocal leukoencephalopathy), in which multiple neurologic problems often lead to a quick death. JC virus targets oligodendrocytes, leading to demyelination and white matter damage in the brain, seen as nonenhancing lesions on MRI.

Others;

• Cryptococcal meningitis is a common cause of HIV/AIDS meningitis, but would manifest with typical meningitis features (fever, headache, nuchal rigidity) and a lumbar puncture consistent with a fungal origin.
• Herpes simplex virus can cause temporal lobe encephalitis with similar speed and severity to PML, but with different radiographic findings and response to treatment.
• Pneumocystis jirovecii can cause pneumonia in HIV/AIDS patients, but rarely causes neurologic symptoms as seen in this patient.
• Toxoplasma gondii can cause encephalitis, but features multiple ring-enhancing lesions, a slower fatal evolution, seizures, and headache.

Question 38

An unconscious 40-year-old man is brought to the emergency department by his wife. She states that her husband complained of severe muscle aches, fever, chills, and headache of sudden onset 4 days earlier. Last night, he developed a dry cough. She also notes that he recently went to clean out their cabin in rural Colorado. Vital signs include blood pressure of 130/90 mm Hg, heart rate of 125, respiratory rate of 28, and temperature of 40°C (104°F). Physical examination reveals inspiratory crackles in both lungs. A chest x-ray shows bilateral interstitial pulmonary edema.

To which infectious agent was the patient most likely exposed?

Answer 38

Hantavirus (bunyaviridae family)

Hantavirus is contracted through exposure to deer mouse droppings or urine. Hantavirus causes HANTAVIRUS PULMONARY SYNDROME, which starts with fevers, headaches, severe myalgias, gastrointestinal upset, and dizziness. As the disease progresses, the virus causes capillary leak syndrome in the lungs resulting in pulmonary edema.

The other options are incorrect.

• Plasmodium falciparum is the protozoan responsible for malaria. Patients present with paroxysms of fever, shaking chills, and sweating. Pulmonary edema may be present, but malaria is unlikely in the United States, since malaria eradication programs succeeded by 1951.
• The other viruses do not present with bilateral pulmonary edema. - Alphavirus is responsible for viral encephalitis, which presents with a sudden onset of headache, high fever, chills, and vomiting, which may progress to disorientation, seizures, or coma.
• Patients infected with a flavivirus will typically present with acute fever, gastrointestinal symptoms, and headache.
• Infection with West Nile virus presents with signs of encephalitis, gastrointestinal distress, and fever.

Question 39

A 53-year old woman presents with hematuria and flank pain. She has a history of recurring urinary tract infections. The X-ray image obtained is shown here= STAGHORN CLACULUS - large radiopaque object.

Which of the following microorganisms is most likely to be cultured from the urine?

Answer 39

Proteus

STRUVITE STONES are caused by infection by urease-producing microorganisms, most commonly, Proteus, Klebsiella, and Staphylococcus.

Question 40

56-year-old man presents with sharp substernal chest pain radiating to his back and arms. The patient is seated and leaning forward. He states that the pain is less severe in this position and worsens when he lies down and takes a deep breath. He recently recovered from a weeklong illness with symptoms of runny nose, cough, and fever. On physical examination, the sound in the audio clip is heard at the left lower sternal border (SCRATCHY, leathery sound during systole and diastole). An ECG shows diffuse ST-segment elevation.

Which of the following describes the microorganism that is the most likely cause of this condition?

Answer 40

Small, naked, single-stranded RNA virus

PERICARDITIS causes precordial chest pain, friction rub, diffuse ST-segment elevations on ECG, pulsus paradoxus, and distant heart sounds. It is often associated with infections, including COXSACKIEVIRUS B (smallest RNA virus), an RNA virus in the picornaviridae family.
**Also common cause of viral myocarditis

Others;

• Catalase-positive, coagulase-positive cocci describes S. aureus, which typically causes endocarditis.
• Double-stranded, linear, enveloped, icosahedral DNA virus describes herpesviridae, including cytomegalovirus and Epstein-Barr virus.
• Double-stranded, segmented RNA virus describes reoviridae. Rotavirus (a member of this family) can cause diarrhea in children.
• Positive, single-stranded, helical RNA virus describes the structure of coronaviridae. A coronavirus typically causes a cold-like syndrome.

Question 41

A 72-year-old man from rural Pennsylvania comes to the emergency department with fever, headache, and fatigue. On physical examination, a large maculopapular rash on his back and buttocks is noted. Upon further questioning, the physician discovers that the patient has several dogs that sleep on his bed with him at night. He recently found several dead ticks in his carpet, but he does not recall seeing any tick bites on himself. He is given a prescription for doxycycline, and his symptoms resolve after 2 weeks. A micrograph of one of the patient’s pretreatment blood samples is shown below = BERRY LIKE CYTOPLASMIC INCLUSIONS IN NEUTROPHILS

**Patient contracted what?

Answer 41

Ehrlichiosis

Ehrlichiosis is associated with fevers, headaches, malaise, and myalgias. A macular, maculopapular, and/or petechial rash may occur on the trunk, legs, arms, or face. Blood may also show berry-like cytoplasmic inclusions in macrophages or neutrophils.

Others

• Babesiosis is a tick-borne illness that presents with fevers, chills, myalgias, and gastrointestinal symptoms, such as anorexia, nausea, and dark urine. It is known to cause hemolytic anemia, thrombocytopenia, and increased serum creatinine and BUN.
• Lyme disease is caused by Borrelia burgdorferi and produces a characteristic target lesion known as erythema chronicum migrans.
• Rocky mountain spotted fever, caused by Rickettsia rickettsii, usually causes a characteristic rash that involves the soles and palms.
• Typhus fever is caused by members of the genus Rickettsia and is associated with transmission through the feces of fleas and lice. It is usually associated with cramped, unsanitary conditions or exposure to flea-carrying rats.

Question 42

25-year-old sexually active woman presents to the emergency department with complaints of worsening dysuria and urinary frequency. The patient states the symptoms began a day ago after she had protected sex with her boyfriend. She denies fever, chills, abdominal pain, and flank pain. The patient has a medical history significant for type 2 diabetes, polycystic ovarian syndrome, and recurrent urinary tract infections (UTIs). Over the past 2 years she has been treated six times for cystitis and once for pyelonephritis.
Vital signs on entry to the emergency department are as follows: temperature of 98.7°F (37°C), blood pressure of 122/82 mm Hg, heart rate of 88, and respiratory rate of 16. The physical exam is significant for suprapubic tenderness, but no costovertebral angle tenderness is detected. Dipstick urinalysis is positive for nitrites and leukocyte esterase.
**FORM PINK COLONIES ON MacCONKEY AGAR

Which of the following is characteristic of the microorganism that most likely causes her infections?

Answer 42

It will ferment lactose.

E coli, which ferments lactose, is the most common cause of urinary tract infections in sexually active young women.

The other characteristics listed are not typical of E coli.

• Growth at 42°C is characteristic of Campylobacter jejuni.
• Bile insensitivity and variable hemolysis are characteristics of Enterococcus.
• α-Hemolysis is characteristic of Streptococcus pneumoniae.
• Dark-field microscopy is used to visualize Treponema pallidum.
• Oxidase positivity and maltose fermentation are characteristic of Neisseria meningitidis.

Question 43

A 17-year-old girl who moved from rural India two years ago is accompanied to the doctor’s office by her sister because of a 6-month history of severe frequent jerking movements in the arms and legs. The sister also reports that, over the past year, the patient’s memory has been worsening and that she has on several occasions gotten lost while walking home from school. Upon further questioning, the patient and her sister are unsure of their childhood vaccination status.

Infection with which of the following agents is most likely responsible for this patient’s presentation?

Answer 43

Rubeola virus

Subacute sclerosing panencephalitis (SSPE) is a sequela of rubeola, or measles virus, and can be detected by the presence of oligoclonal bands in CSF. High titers of measles antibodies are often present in the serum of affected patients. Be suspicious of SSPE in a patient who has an unknown vaccination history, is from an endemic area, and presents with myoclonus and worsening dementia.

OTHERS

• JC virus causes progressive multifocal leukoencephalopathy and manifests in altered mental status, motor deficits, and visual symptoms. It rarely affects immunocompetent persons. Poliovirus infection is characterized by flaccid paralysis and muscular atrophy.
• Rabies virus spreads from the site of the initial bite from an infected animal to motor and sensory neurons and can lead to convulsions, paresthesias, cognitive effects, and flaccid paralysis; the time course of this patient’s illness is extremely slow for rabies.
• The rubella virus, if acquired antenatally, can lead to congenital rubella syndrome, which is characterized by ophthalmologic and cardiac defects and fetal mortality.

Question 44

32-year-old man presents to the emergency department with shortness of breath and says his heart is “beating too hard.” He and his family recently immigrated from Peru, and his medical history is unknown. On physical examination, tachypnea and palpitations are noted. X-ray of the chest demonstrates pulmonary congestion.
Echocardiography reveals biventricular dilatation. An endomyocardial biopsy specimen reveals the presence of intracellular protozoan parasites. Heart catheterization is performed, revealing a pulmonary capillary wedge pressure (PCWP) of 20 mm Hg.

Which vector is most likely responsible for transmitting this patient’s disease?

Answer 44

Reduviid bug

Chagas disease, which manifests with myocarditis, achalasia, and megacolon, is caused by T. cruzi, which are intracellular protozoan parasites transmitted by reduviid bugs.

OTHERS

• The Aedes aegypti mosquito can spread Zika virus, but it is most commonly linked to the birth defect microcephaly.
• The Ixodes tick commonly causes babesiosis and Lyme disease.
• Phlebotomus sandflies are associated with visceral and cutaneous leishmaniasis.
• Tsetse flies are associated with African trypanosomiasis and may cause lymphadenopathy and somnolence.

Question 45

18-year-old woman is recovering in the intensive care unit after being involved in an automobile accident that occurred 6 days ago. She has a left femoral head fracture, multiple rib fractures, a C1 fracture, concussion, and superficial lacerations. The patient has two large-bore IV lines in her antecubital fossa bilaterally, a Foley catheter, and a nasal cannula. She received two units of blood the day after the accident. She has been alert and oriented to person, place, and time until this morning when she did not recognize her nurse and became confused and agitated. Her temperature is 101.3°F (38.5°C), blood pressure is 110/78 mm Hg, pulse is 89/min, respiratory rate 18/min, and oxygen saturation 99% on 2 L oxygen. Cardiovascular and respiratory examinations are normal; however, the patient winces on palpation of the lower abdomen. Her extremities are warm and capillary refill time is <2 seconds. This morning’s laboratory results are shown.

A culture for the suspected bacteria is performed on bile esculin agar.

Answer 45

Enterococcus

Enterococcus is a common cause of catheter-associated and other nosocomial UTIs, which present with fever and lower abdominal pain. Nitrites will be absent on urinalysis and the pathogen can be cultured on bile esculin agar.

Question 46

27-year-old woman from South Korea presents to her primary care doctor for her first visit. She is in good health and denies any current symptoms. However, she notes that several months ago she had severe abdominal pain that has since completely resolved. The pain was intermittent and lasted for several months and was not associated with nausea or vomiting. Her physician orders a hepatitis panel, given this patient’s history of abdominal pain. Results of serologic testing are:

hepatitis serology is significant for the presence of anti-HBs and anti-HBc. Anti-HBs suggests prior exposure to or vaccination against hepatitis B; however, the presence of anti-HBc is indicative of prior exposure

Which of the following is the appropriate conclusion?

Answer 46

The patient has been exposed to hepatitis B virus and has completely recovered.

The presence of both anti-HBs and anti-HBc without hepatitis B antigens suggests prior infection with complete recovery.

Question 47

A mother brings her 7-year-old son to the pediatrician because he has had difficulty sleeping for 1 week. Further questioning reveals that the child has experienced increasing bouts of perianal itching, which occur at night and disrupt his sleep. His mother denies contact with sick children at school but notes he did attend a sleepover at a friend’s house a week ago. She also denies any changes in her son’s diet or bowel habits. Physical exam reveals mild erythema around the anus but no anal fissures or bleeding. The physician instructs the mother to apply cellophane tape to the child’s anal area at night when the itching occurs and to bring the tape back for analysis the next day. The pediatrician observes the findings shown in the image with a microscope.

In addition to treating the child, what treatment should the pediatrician prescribe for the child’s family should they have symptoms as well?

Answer 47

Mebendazole

Enterobius vermicularis (PINWORMS), causes severe anal pruritus, which tends to be worse at night. It can be diagnosed with the “Scotch tape test” and is treated with albendazole, mebendazole, or pyrantel pamoate.

OTHERS

• Benznidazole is the treatment for Chagas disease, which is most commonly seen in South and Central America. It can lead to conditions such as dilated cardiomyopathy or megaesophagus but does not generally cause pruritis ani.
• Doxycycline is usually the first-line treatment for many tick-borne diseases; however, this patient had a positive “Scotch tape test,” which confirmed a pinworm infection.
• Although ivermectin may have some efficacy against Enterobius vermicularis, it is mainly used to treat Onchocerca volvulus and is not first-line treatment for pinworm infections.
• Niridazole is used for the treatment of Dracunculus medinensis, which can cause intense subcutaneous burning and skin ulceration but does not cause perianal itching as reported for this patient.

Question 48

A 79-year-old man presents to his physician and says that he has been coughing up rust-colored mucus for the past week. He also reports shortness of breath and sharp chest pain that worsens when he breathes or coughs. He has a 25-year history of hypertension that is managed with lisinopril. He also takes daily vitamin supplements. He appears malnourished. He does not smoke cigarettes but drinks a couple of beers every weekend. His temperature is 38.2°C (100.7°F), blood pressure is 132/84 mm Hg, and heart rate is 108/min. On physical examination, the patient’s breathing appears labored and he is using his accessory muscles to breathe. There are diffuse wheezes on auscultation. No dullness or hyperresonance are noted on percussion. No edema, jugular vein distention, or hepatomegaly are present. Blood tests show a left shift with increased numbers of neutrophils. Results of a sputum culture are shown below and an x-ray of the chest shows a lobar effusion = lancet shaped diplococci

Which of the following is characteristic of this patient’s type of pneumonia?

Answer 48

It is the most frequent cause of lobar pneumonia

The most common organism causing lobar pneumonia is Streptococcus pneumoniae. Lobar pneumonia is characterized by shortness of breath, a cough productive of rust-colored sputum, Atypical pneumonia, by contrast, is more often caused by Mycoplasma, Chlamydia, or viruses.

OTHERS

• The other answer choices are associated with ayptical pneumonia, which is associated with inflammation of the interstitium. Atypical pneumonia typically does not cause consolidation of the lung.
• Lobar, rather than patchy, consolidation is seen in pneumococcal pneumonia.
• Atypical pneumonia is typically caused by viruses and bacteria such as Mycoplasma pneumoniae and Chlamydia pneumoniae, which do not appear on Gram stain.

Question 49

A 22-year-old woman presents to her physician because of a rash (see image). On questioning, she reports having unprotected sex with five partners within the past year. Several months ago, she noticed a single painless and firm lesion on her labia that resolved without treatment. Her vital signs are as follows:
Temperature: 101°F (38.3°C)
Heart rate: 87
Respiratory rate: 17
Blood pressure: 132/82 mm Hg

She has swollen nontender submandibular, axillary, and inguinal lymph nodes. The physician prescribes the appropriate treatment, but the patient refuses it because she believes she’ll get better with time.

If treatment is not begun, this patient is at increased risk for developing which of the following?

Answer 49

Aortic insufficiency

Secondary syphilis can present with fever, sore throat, malaise, a generalized maculopapular rash involving the palms and soles, condylomata lata (wart-like papules on the genitals), and generalized nontender lymphadenopathy. Syphilis infections can lead to aortic insufficiency as a result of destruction of the vasa vasorum.

OTHERS

• Migratory arthritis is classically associated with Neisseria gonorrhoeae infection. Although disseminated gonorrhea can sometimes cause a pustular rash, it usually spares the palms and soles and would not be preceded by a painless genital lesion.
• Coronary aneurysms can be seen in patients with Kawasaki disease. Although this patient has a fever, adenopathy, and hand and foot changes, she is an adult with a history of a painless genital lesion, making Kawasaki disease less likely.
• Transient monocular blindness is often due to atherosclerotic vascular disease in patients with hypertension, hyperlipidemia, diabetes, and coronary artery disease. This patient is young and has no risk factors, making it a less likely diagnosis.
• Aseptic meningitis can result from infection with coxsackievirus. Coxsackievirus presents commonly in children with fever and oval-shaped vesicles on the palms and soles. This patient is an adult with generalized lymphadenopathy and a history of a painless genital lesion, making coxsackievirus infection less likely.

Question 50

32-year-old woman presents to the clinic with sore throat, low-grade fever, fatigue, and malaise for the past month. Other than occasional treatment for bacterial trichomonas vaginosis, she does not have any notable medical history. Her social history is significant for occasional alcohol use, no illicit drug use, and multiple sexual partners.
On examination she is found to have generalized lymphadenopathy and the non-tender lesions seen in the image. The patient denies any generalized joint pain.

If left untreated, which of the following is a possible sequela of the most likely cause of her symptoms?

Answer 50

Aortic infarction

Secondary syphilis can present with widely distributed nonpruritic, red, discrete, macules that are classically seen on the palms and soles, but may also appear on the trunk or proximal extremities. Other common symptoms and signs include low-grade fever, sore throat, generalized lymphadenopathy, malaise, condylomata lata, and silver-gray mucosal lesions. Syphilis can cause skin, bone, liver, testes, neurological, and cardiovascular complications–including aortic infarctions.

OTHERS
- AIDS is the the most advanced stage of HIV infection and is diagnosed with a CD4+ count <200. Patients with AIDS often present with increased susceptibility to minor infections. This patient shows no signs of a compromised immune system.

• Cervical carcinoma is secondary to HPV infection and is localized to the cervix without any major generalized lymphadenopathy or malaise, as seen in this patient. This patient’s genital lesions and those seen on her palms, are typical of a rash, not of verrucae (warts).
• Perihepatitis, also called Fitz-Hugh-Curtis syndrome, is a complication of pelvic inflammatory disease, and usually presents with right upper quadrant pain. In women, it is closely associated with pelvic inflammatory disease caused by chlamydia or gonorrhea. A rash is not typically associated with this condition.
• Pelvic inflammatory disease is a complication of uncontrolled gonorrhea, chlamydia, or vaginosis. It presents with severe adnexal tenderness. Cutaneous lesions on the extremities are not pathognomonic for this disease, but are associated with secondary syphilis.

Question 51

A 13-month-old girl is brought to the pediatrician because of fever and a sore throat. Her mother confides that the child has always been healthy and has never needed any immunizations. However, over the past several days, the child is less active and refusing to eat. Today her neck appears swollen. Examination reveals a grayish membrane-like material in the posterior pharynx. The pathogen most likely responsible for this child’s illness is normally not virulent unless it undergoes a certain process.

Which of the following organisms can increase its pathogenicity by the same process as the bacteria causing the condition in the question?

Answer 51

Group A streptococci

The pathogenesis of certain bacteria is dependent on the expression of a temperate bacteriophage exotoxin, a process known as LYSOGENIC CONVERSION. Examples include diphtheria (Corynebacterium diphtheriae), scarlet fever (Streptococcus pyogenes), botulism (Clostridium botulinum), and cholera (Vibrio cholerae).

Question 52

A 17-year-old boy presents with fever and pain on both of his cheeks. He finds it hard to talk, eat, and swallow. He denies feeling like he has a headache or any neck pain. He has recently emigrated from Mexico, and one of his relatives had a similar illness a few weeks ago. In Mexico, he had questionable access to healthcare as a child. His temperature is 38.8°C (101.8°F), his blood pressure is 118/72 mm Hg, and his heart rate is 90/min. Physical exam shows a bilaterally tender and swollen mandibular area.

Which of the following findings might also be present on examination?

Answer 52

Orchitis

Complications of a mumps infection include parotitis, orchitis, pancreatitis, and meningitis. Because of routine measles/mumps/rubella vaccination, mumps is relatively uncommon in the United States.

Question 53

A 73-year-old woman is admitted to the hospital because of an acute exacerbation of congestive heart failure. A central venous catheter is inserted on the second hospital day. On hospital day 6, the nurse notes that the patient can no longer recall her name and is confused about where she is. The patient’s temperature is 38.9°C (102°F), pulse is 95 beats/min, respirations are 24 breaths/min, and blood pressure is 130/90 mm Hg. Blood culture reveals a gram-negative rod that produces a red pigment.

Which of the following organisms is the most likely cause of this patient’s infection?

Answer 53

Serratia marcescens

Serratia marcescens is a common cause of catheter-related infection

Question 54

28-year-old white man presents to his family physician complaining of painful urination. Physical examination reveals a purulent urethral discharge. Gram stain demonstrates infection with Neisseria gonorrhoeae. An HIV test is positive.

Which of the following genotypes would have helped prevent this patient from contracting HIV?

Answer 54

Homozygous for the CCR5 mutation

People who are homozygous for mutations of the CCR5 receptor on macrophages are immune to certain strains of HIV.

Question 55

A patient with fulminant sepsis is brought to the emergency department and transferred quickly to the intensive care unit. Blood cultures yield two strains of virulent bacteria. Bacterial strain X is resistant to ampicillin and sensitive to gentamicin. Bacterial strain Y is resistant to gentamicin and sensitive to ampicillin. Bacterial strains X and Y are grown in mixed cultures, in medium without antibiotics, and then the culture is plated on medium containing both ampicillin and gentamicin. Bacterial colonies grow on the plates. In a second experiment, separate strains of X and Y are co-cultured in DNAse-containing antibiotic-free media, then plated on culture medium containing ampicillin and gentamicin. No colonies grow on these plates.

Assuming that bacterial cells are impermeable to DNAse, which of the following processes best explains these observations?

Answer 55

Transformation

Transformation occurs when a cell takes up DNA from a donor cell. When two types of bacteria are grown in mixed culture, some might survive bactericides that could kill each type individually, unless DNAse is added to destroy DNA spilled into the medium before cells can absorb it.

Question 56

newborn girl is brought to the pediatrician by her mother because of purulent umbilical discharge that started one day earlier, with fever, irritability, and diffuse flushing. Today, she is covered in large, fluid-filled blisters that rupture easily, leaving raw red areas beneath. Blood cultures grow an organism and the results are shown.

The skin symptoms observed in this case are due to the involvement of which of the following structures?

Answer 56

Desmosomes

In staphylococcal scalded skin syndrome, the epidermis separates at the stratum granulosum as a result of binding of epidermolytic toxins A and B to desmoglein 1 (desmosomes) in this layer.

Question 57

A 46-year-old man comes to the clinic with a temperature of 38.6°C (101.5°F). The patient reports no sick contacts but does mention a dentist appointment a few days ago. On further questioning, the physician discovers that the man had rheumatic fever as a child. Physical examination reveals tender raised lesions on the pads of his fingers and toes and painless, erythematous lesions on his palms and soles. A new heart murmur is heard on auscultation. Blood cultures are drawn.

Which of the following describes the most likely causative organism for this patient’s condition?

Answer 57

Gram-positive cocci, catalase-negative, a-hemolytic, optochin-resistant

Viridans streptococci are a group of gram-positive cocci, catalase-negative, α-hemolytic, and optochin resistant. They can cause subacute endocarditis, generally in the setting of previously diseased heart valves and recent dental procedures.

Question 58

27-year-old G2P1 woman at 34 weeks’ gestation visiting from Thailand dies 2 weeks after after coming for evaluation of a 1-week history of nausea, vomiting, and watery diarrhea with abdominal pain. She had arrived in the United States 2 weeks prior. Temperature was 37°C (98.6°F). On physical examination, she had icteric sclerae and jaundice. No lower-extremity edema or jugular venous distention were observed. Results of a stool test were negative for ova and parasites, and the stool and blood cultures were negative for pathogenic bacteria. Laboratory values showed increased liver enzymes (aspartate transaminase and alanine transaminase).

Which of the following histologic findings is most likely to be noted during the autopsy?

Answer 58

Hepatic tissue necrosis

Hepatitis E can be fatal, particularly to pregnant women, due to cirrhosis, which is seen as patchy necrosis on biopsy.

Question 59

4-year-old girl is brought to the pediatrician after experiencing abdominal pain, vomiting, and diarrhea containing mucus and blood for the past 3 days. Several children in her daycare class have similar symptoms. Her temperature is 39.4°C (103°F). On examination she has lower abdominal tenderness and decreased bowel sounds. Stool culture and Gram stain reveal a straight, Gram-negative, oxidase-negative rod that produces white colonies on MacConkey agar, and does not cause blackening on triple sugar iron (TSI) slant.

This patient is at increased risk for which of the following complications?

Answer 59

Renal failure, microangiopathic hemolytic anemia, and thrombocytopenia

Shigella is an invasive, Gram-negative non-lactose fermenter that does not produce hydrogen sulfide, and can cause dysentery with fever. Shigella dysenteriae also produces a toxin that may cause hemolytic uremic syndrome, which manifests with the typical triad of anemia, thrombocytopenia, and acute renal failure.

Question 60

A microbiology laboratory is investigating the possibility of using enzymes as a novel class of antibacterial agents. These enzymes work by destabilizing the bacterial cell membrane through binding directly to cell surface peptidoglycans and hydrolyzing bonds within them. These enzymes cannot traverse double-layer lipid membranes.

Which of the following organisms would be affected by this type of drug?

Answer 60

Staphylococcus aureus

A gram-positive bacterium, such as Staphylococcus aureus, would be most susceptible to a hypothetical antibiotic that hydrolyzes surface peptidoglycans because its outermost structure is a thick peptidoglycan cell wall. An intracellular bacterium, a bacterium without a cell wall, or a gram-negative bacterium with a thin peptidoglycan cell wall enclosed by an outer membrane would not be susceptible to the enzymes being investigated.

Question 61

33-year-old homeless man is brought to the emergency department by a friend. The friend reports that although the patient is HIV positive, he has never seen him taking any medication. The patient’s initial complaints centered on generalized weakness and vision difficulties, which started several weeks ago. Over time, the patient lost his peripheral vision and became unable to talk or walk. The man appears disheveled and is not oriented to person, place, or time. A lumbar puncture is performed, and cerebrospinal fluid analysis results are as follows:
Opening pressure: 85 mm Hg
Glucose: 43 mg/dL
Protein: 36 mg/dL
Leukocytes: 3 cells/μL

His CD4 count is 35/mm3. Magnetic resonance imaging of the brain is performed, and findings are shown below.

Which of the following is the most likely diagnosis?

Answer 61

Progressive multifocal leukoencephalopathy

In severely immunocompromised patients with subacute altered mental status, neurologic deficits, visual and motor changes, and ataxia, progressive multifocal leukoencephalopathy should be considered as a diagnosis. It is caused by the reactivation of JC virus when the CD4+ count is < 200/mm3. Neuroimaging reveals multiple, nonenhancing white matter lesions with a normal cerebrospinal fluid profile.

Question 62

37-year-old man with a history of HIV infection is brought to the emergency department by his neighbor because of unusual behavior and disorientation. The patient also has a history of noncompliance with his HIV medication. On physical examination, he exhibits weakness of the right upper and lower limbs, disorganized meaningless speech, and ataxia. He is admitted to the hospital and experiences multiple focal seizures during his stay. Urine toxicology is negative, but blood tests reveal a second infection. MRI reveals high signal intensity in the temporal lobes and hippocampus. His CD4 count is 78 cells/mm3.

During its latency period, which of the following components of the superinfecting virus can be detected in infected neurons?

Answer 62

Double-stranded DNA virus

During the latent phase, HSV-1 viral genetic material is preserved as an episome: circular, double-stranded DNA that is not yet integrated into the host chromosome and therefore can be detected in infected neurons.

Question 63

A newborn boy is brought to the pediatrician for evaluation of an extensive skin rash. Questioning of the infant’s mother reveals that early in her pregnancy, she had a fever and sore throat with generalized fatigue for a few days. Physical examination shows that this infant has microcephaly, hearing loss, and a petechial skin rash. Auscultation reveals normal heart and breath sounds. The abdominal examination reveals hepatosplenomegaly.

Which of the following is the most likely diagnosis?

Answer 63

Congenitally acquired cytomegalovirus

Congenital CMV infection manifests in neonates as hearing loss, seizures, petechial rash, microcephaly, and evidence of periventricular calcifications on CT of the head. Maternal manifestation may include a mononucleosis-like illness during pregnancy.

• *TORCHES infection (toxoplasma Gondi, rubella, CMV, HIV, HSV2, syphilis)
• Congenitally acquired rubella is associated with cataracts, hearing loss, and congenital heart disease.
• Congenitally acquired herpes simplex virus is associated with neonatal meningoencephalitis and vesicular, herpetic lesions.
• Congenitally acquired HIV presents as recurrent infections and chronic diarrhea in neonates.
• Congenitally acquired syphilis often results in stillbirth and hydrops fetalis. If the infant survives, he or she will have notched teeth, a saddle nose, saber shins, and sensorineural deafness.

Question 64

28-year-old woman who is at 8 weeks’ gestation with her second pregnancy comes in for a check-up after feeling unwell for the past 2 weeks. She reports being more tired than usual and has a persistent headache and a mild fever. Her temperature is 100.4°F (38°C), blood pressure is 127/81 mm Hg, pulse is 73/min, and respiratory rate is 15/min.
Physical examination is remarkable for mild cervical lymph node enlargement. Laboratory tests reveals agglutination of horse erythrocytes when mixed with the patient’s serum. The patient continues with routine prenatal care and later gives birth to a healthy child.

To which of the following pathogens was the patient most likely exposed?

Answer 64

enveloped DNA virus

Epstein-Barr virus is a double-stranded DNA virus that yields a positive Monospot test during infection (the patient’s serum causes horse erythrocytes to agglutinate). EBV is not included in the ToRCHeS infections.

Question 65

A 29-year-old woman presents to the emergency department with a 9-hour history of worsening lethargy and a throbbing headache. On arrival, the patient’s temperature is 102.4°F (39.1°C), blood pressure is 102/68 mm Hg, and heart rate is 97/min. On physical examination the patient has tense neck stiffness and several small red spots on her trunk and arms that do not blanch with pressure. A lumbar puncture is performed.

Using the table above, which of the following are the most likely findings on CSF analysis?

Answer 65

Symptoms of bacterial meningitis include fever, headache, nuchal rigidity, and a nonblanching petechial rash. CSF analysis shows an elevated opening pressure, elevated protein, decreased glucose concentration, and significant pleocytosis of WBCs with a predominance of neutrophils.

• opening pressure ; 250
• WBC - 500 (90% PMNs)
• Protein 55
• Glucose low

Question 66

12-year-old boy is brought to the emergency department by his mother after 3 days of fever and delirium. The patient reports weakness and a severe sore throat that makes him feel like he is gagging. His mother notes that 2 months earlier, their family took a trip where they went hiking, camping, and cave-exploring. The boy developed fever, chills, nausea, and lethargy shortly after returning home, but they did not seek medical attention at the time, and the symptoms subsided. Over the past 3 days, he has experienced decreased oral intake and rapid weight loss. On physical examination, the patient appears agitated and acutely ill. His mother reports that his routine immunizations are up to date. The emergency physician recommends immediate treatment.

What pathogen is most likely responsible for this patient’s condition

Answer 66

Enveloped single-stranded RNA virus

Rabies infection manifests early with a nonspecific prodrome, followed by a long incubation that slowly progresses to severe encephalitis with hydrophobia. The rabies virus is a member of the rhabdovirus viral family, which are single-stranded, enveloped, and helical.

Question 67

32-year-old pregnant woman develops an illness after ingesting river water on a trip abroad. Her symptoms include jaundice, anorexia, fever, severe abdominal pain, nausea, vomiting, and malaise. Many other people on the trip experienced similar, but less severe, symptoms. She is admitted to the hospital and spends 2 weeks in the intensive care unit (ICU) before her condition is stabilized. Laboratory tests at admission show an alanine aminotransferase level of 600 U/L and an aspartate aminotransferase level of 420 U/L.

What type of virus did this woman most likely contract?

Answer 67

Nonenveloped, single-stranded RNA virus

Hepatitis E is a nonenveloped, single-stranded RNA hepevirus that is spread by the fecal-oral route, is most commonly water-borne, and is associated with a high mortality rate in pregnant women.

Question 68

10-year-old boy is referred to a neurologist after declining school performance, generalized seizures, and visual disturbances that have worsened during the past few months. Analysis of cerebrospinal fluid analysis shows a WBC count of 2 cells/uL, glucose level of 50 mg/dL, and protein of 30 mg/dL; culture shows no bacterial growth. The patient is afebrile and does not report having a headache. On further questioning, his mother notes that he was adopted from Eastern Europe at age 4, and she was never able to acquire his medical records. She remembers him developing a rash resembling the one shown in the image soon after he was adopted.

Which of the following is the most likely etiology of this patient’s current condition?

Answer 68

Measles virus

Subacute sclerosing panencephalitis is a rare complication of prior measles infection that causes progressive neurologic disease leading to death. CSF exams usually reveal normal pressure, cell count, and total protein content. However, CSF globulin is almost always elevated, constituting up to 20%–60% of CSF protein.

Question 69

46-year-old woman is brought to the emergency department because she has had difficulty “catching her breath.” The patient says she’s been feeling very warm and lethargic for the past 2 days and has not been able to eat because of nausea and vomiting. She also reports having a dry, non-productive cough. Medical history is significant for receiving a bone marrow transplant 2 months ago. Vitals signs are as follows:

Heart rate: 88/min
Blood pressure: 100/74 mm Hg
Temperature: 39.4°C (103°F)
Respiratory rate: 26/min
SpO2: 92% on room air

A chest x-ray shows bilateral, symmetrical lower lobe peribronchovascular and alveolar processes. Bronchoalveolar lavage is performed and the results are shown below.

Answer 69

Latent in mononuclear cells

Cytomegalovirus (CMV) is an enveloped double stranded linear DNA virus that is latent in mononuclear cells. It is seen histologically as large cells with intranuclear inclusions (“owl′s eyes”) and is a common cause of pneumonia in immunocompromised patients (CMV pneumonitis), especially those 1-4 months post-transplant.

Question 70

21-year-old woman comes to the clinic because of a painful ulcer on her lower lip for the past 3 days. On further questioning, she states that she has experienced identical symptoms in the past with painful vesicles organizing into ulcers over a 1–2-week period. An image of the biopsy sample taken from the lesion is shown.

Image = multnucleated giant cells and intranuclear inclusions

The pathogen affecting this patient is also known to cause which of the following manifestations?

Answer 70

Keratoconjunctivitis

Infection with herpes simplex virus type 1 (HSV-1) may cause herpes labialis (cold sores), which are recurrent ulcers localized on the lips. HSV-1 infection can also manifest as keratoconjunctivitis, temporal lobe encephalitis, or gingivostomatitis. Biopsy of an HSV lesion shows characteristic multinucleated giant cells and intranuclear inclusions.

Question 71

70-year-old man presents to his physician because of difficulty breathing, fever, and chills. His symptoms began 2 days ago and have been getting progressively worse. He states that he also has a constant headache, and intermittent nausea, vomiting, and diarrhea. His temperature is 39°C (102.2°F), blood pressure is 102/72 mm Hg, pulse is 72/min, respiratory rate is 22/min, and SpO2 is 96% on room air.
The patient is treated with oseltamivir, and his symptoms resolve over the next 4 days. However, 2 days after the resolution of his symptoms the patient returns to the physician’s office, this time with worsening dyspnea, SpO2 of 90% on room air, and a productive cough with mucopurulent sputum. A chest X-ray reveals bilateral lower lobe consolidation. The patient is admitted to the hospital and treated with intravenous antibiotics.

Which of the following best describes the structure of the viral genome that most likely caused his initial illness?

Answer 71

Enveloped, segmented, negative-sense, single-stranded RNA

Influenza is an enveloped, segmented, negative-sense, single-stranded RNA virus that affects tracheobronchial epithelium leading to destruction of alveoli and loss of cilia, which can cause a secondary bacterial pneumonia.