Infectious Disease

Question 1

A neonate with meningitis grows Citrobacter in her blood culture.

What is the next test you should order?

Answer 1

CT or MRI of the head
Explanation
You should be very concerned about a brain abscess; therefore, order a CT or MRI of the head. Brain abscesses occur in ~ 75% of Citrobacter meningitis cases.

Question 2

A child with a cochlear implant is at increased risk of central nervous infection from what organism?

Answer 2

Streptococcus pneumoniae
Explanation
S. pneumoniae is a normal inhabitant of the upper respiratory tract and is a common cause of acute bacterial otitis media, sinusitis, and pneumonia in children < 5 years of age. Children with cochlear implants have an increased risk of pneumococcal meningitis.

Question 3

A child presents with bacteremia due to methicillin-resistant Staphylococcus aureus (MRSA).

What is the antibiotic of choice

Answer 3

Answer
IV vancomycin
Explanation
Newer agents are available, but for children, vancomycin remains the drug of choice for the treatment of MRSA bacteremia

Question 4

A child from Connecticut presents with an isolated 7th cranial/facial nerve palsy.

What diagnosis should you consider as the etiology of the facial palsy?

Answer 4

Answer
Lyme disease
Explanation
Neurological problems can be symptoms of early disseminated (Stage 2) Lyme disease. Consider Lyme disease as a possible etiology if you see isolated facial nerve palsy, which may be the only manifestation, and/or foot drop in a patient from an endemic area

Question 5

A NICU infant is found to have an IV catheter infection with Candida albicans.

How should this infection be managed?

Answer 5

Remove the catheter and start systemic antifungals.
Explanation
The key point here is that with fungal line infections, the catheter must be removed. Do not try to “treat through” and clear the catheter infection without removing the catheter. Amphotericin B deoxycholate is the preferred empiric choice for neonates, but fluconazole can be used if the organism is found to be susceptible. Treat for at least 2 weeks for isolated candidemia, and at least 3 weeks if there is multi-organ disease or meningitis.

Question 6

A 15-year-old boy who lives and works on a sheep farm presents with a painless papule that vesiculates and forms a painless ulcer, then a painless black eschar with nonpitting, painless induration and swelling.

What is the likely diagnosis?

Answer 6

Anthrax
Explanation
Anthrax inoculation occurs from handling contaminated hides/wool. It can progress to septicemia and meningoencephalitis if left untreated. The cutaneous form (95% of cases) presents as described. Associated symptoms can include fever, headache, and painful lymphadenopathy

Question 7

What is the most common cause of IV catheter-related bacteremia?

Answer 7

Staphylococcus epidermidis
Explanation
S. epidermidis is usually methicillin resistant. It is the most common cause of both catheter-related bacteremia and postoperative bacteremia, which occurs when foreign material is left in the body (e.g., prosthetics including heart valves and joints, pacemakers, ventriculoperitoneal shunts).

Question 8

40% of the passengers on a cruise ship develop diarrhea.

What is the most likely etiology of the diarrhea?

Answer 8

Norovirus
Explanation
Noroviruses cause ~ 50% of infectious viral gastroenteritis outbreaks in the U.S. and are responsible for the majority of “ship-wide” diarrhea outbreaks on cruise ships. The incubation period is only 1–2 days. Be careful on exams—if they say it is only a few people on a cruise ship who ate at a buffet, it is more likely a preformed toxin-like Staphylococcus or Bacillus species

Question 9

A 4-day-old infant presents with bloody, green discharge from the eyes. He was born at home.

What is the most likely diagnosis?

Answer 9

Gonococcal ophthalmia
Explanation
Gonococcal ophthalmia presents 2–5 days after delivery with bloody, green, or serosanguinous discharge from the eyes. Gram stain the discharge (you would see gram-negative diplococci) and culture for Neisseria gonorrhoeae.

Question 10

A 2-year-old boy presents with enlarged, matted anterior cervical lymph nodes. When combined, they measure about 3 × 6 cm. The nodes are painless. A tuberculin skin test is performed and its diameter of induration is 8 mm. The nodes have been persistent for 2 months despite various courses of antimicrobials, including cephalexin and amoxicillin/clavulanate.

What is the best management at this time?

Answer 10

Answer
Complete excision of the nodes
Explanation
This is lymphadenitis, most likely due to atypical mycobacteria—either Mycobacterium scrofulaceum or M. avium complex. Treat by completely excising the nodes. Do not incise the node, as this causes a chronic draining lesion. If not excised, most recede within 2 years

Question 11

A college student presents with vomiting. He felt ill 1 hour after eating leftover fried rice this morning (which was left on the counter overnight).

What is the likely diagnosis?

Answer 11

Bacillus cereus toxin food poisoning
Explanation
B. cereus is a close relative of B. anthracis. It can cause 2 forms of gastroenteritis:
A short-incubation (1–6 hours) emetic type, due to preformed heat-stable toxin
A longer-incubation (8–16 hours) diarrheal type, due to heat-labile enterotoxin production in vivo in the GI tract
This patient has the emetic form, which often results from consuming cooked rice left at room temperature, especially fried rice. This gastroenteritis is self-limited and only needs symptomatic treatment.

Question 12

What is the best empiric antibiotic therapy for meningitis in any child > 3 months of age?

Answer 12

Answer
IV ceftriaxone or cefotaxime, plus IV vancomycin
Explanation
Empiric therapy for meningitis includes a 3rd generation cephalosporin (ceftriaxone or cefotaxime) plus vancomycin to cover for possible Streptococcus pneumoniae resistance.

Question 13

How many millimeters of induration are considered positive for a tuberculin skin test in a 3-year-old without any risk factors?

Answer 13

≥ 10 mm of induration
Explanation
Remember that children < 4 years of age are part of the moderate-risk group. Others in this group include:
Homeless persons
Those who have recently traveled to or were born in a high-prevalence region for tuberculosis
IV drug users who are HIV-negative
Prisoners
Health care workers; patients and staff of nursing homes
Diabetics; those with chronic renal failure
Persons undergoing immunosuppressive therapy (< 15 mg/day prednisone)

Question 14

15-year-old girl presents with fever, weight loss, weakness, night sweats, and cough. She lives with her aunt, whose spouse returned from jail about 5 months ago.

CXR shows hilar lymphadenopathy with a pleural effusion on the left. A subsequent pleural tap reveals:

2,000 WBC/µL—mostly lymphocytes
Low glucose
Elevated protein
Elevated LDH
Acid-fast bacilli (AFB) smear and culture are negative
What is the most likely diagnosis?

Answer 14

Tuberculosis (TB)
Explanation
The girl has classic findings of TB, and her risk factor is living in a household with someone who was recently incarcerated. If she can produce sputum, stain and culture it for AFB and perform a tuberculin skin test (TST). Pleural biopsy is indicated if the sputum and pleural effusion are not diagnostic. Pleural effusions are typically AFB smear (and culture) negative, while pleural biopsy is much more sensitive for picking up active pulmonary TB.

Question 15

A boy from upstate New York presents with a single erythema migrans lesion. His parents inquire about the value of laboratory testing before treatment.

What is the value of performing serologic testing on this patient?

Answer 15

nswer
None
Explanation
The patient has early localized (Stage 1) Lyme disease, and serology is often negative. Therefore, base the diagnosis on clinical findings. Erythema migrans is a characteristic skin lesion in early localized disease. You do not need to check Lyme serology on a patient with erythema migrans (serology negative 90% in this stage)—just treat!

Question 16

A 6-year-old girl, born and reared in the U.S., has sickle cell disease and presents with:

Fever
Pain and swelling of her left thigh
An MRI reveals osteomyelitis and a subperiosteal abscess
A Gram stain of a bone aspirate reveals gram-negative rods
What is the most likely organism causing her osteomyelitis?

Answer 16

Answer
Salmonella species
Explanation
Osteomyelitis is a bone infection that is usually bacterial in origin. Children with sickle cell disease are at risk for infection with Salmonella (a gram-negative rod), as well as typical organisms such as Staphylococcus aureus (a gram-positive coccus).

Question 17

A 6-year-old with MRSA osteomyelitis is given his first dose of antibiotic. He develops:

Tachycardia
Flushing
Generalized pruritus
What antibiotic was he likely given?

Answer 17

A 6-year-old with MRSA osteomyelitis is given his first dose of antibiotic. He develops:

Tachycardia
Flushing
Generalized pruritus
What antibiotic was he likely given?

Question 18

A 5-year-old presents with:

Abrupt onset of high fever
Sore throat
Odynophagia
Tiny (1–2 mm) vesicles on the anterior pillars of the tonsils, uvula, and pharynx; no vesicles are noted on the front part of the mouth or lips
What is the most likely diagnosis?

Answer 18

wer
Herpangina
Explanation
Herpangina is most often caused by coxsackievirus group A and presents in an abrupt fashion with the symptoms listed here. The pattern of where the vesicles occur differentiates herpangina from herpes simplex gingivostomatitis. In herpes simplex infection, lesions manifest commonly in the front of the mouth and extend onto the lips. In contrast, herpangina involves the back of the mouth, including the tonsils, uvula, and pharynx. Oral vesicles in hand-foot-and mouth (HFM) disease, which can be caused by coxsackieviruses, may involve the palate, buccal mucosa, and tongue but patients usually have the characteristic skin vesicles on their extremities as well

Question 19

A child has a persistent tooth abscess that has been ignored for several weeks. Now, he presents with drainage on the outside skin lateral to the infection of his molar. Stains of the drainage show yellow “sulfur” granules.

What is the most likely diagnosis

Answer 19

Actinomyces
Explanation
Actinomyces is a microaerophilic/facultative anaerobic organism that is part of the oral and gastrointestinal flora. It can cause infections of normally sterile sites, presenting as described here. The characteristically yellow “sulfur” granules are actually clusters of organisms. Actinomyces is most commonly associated with dental infections, but it can also cause pelvic inflammatory disease in adolescents using IUDs

Question 20

A family presents after staying in a rural cabin in southern Colorado; it was summertime, and they had slept with the windows open to enjoy the fresh, cool night air. On awakening the next morning, they found a dead bat in the bedroom where they were sleeping

What should happen next

Answer 20

Give rabies immunoglobulin (RIG) and vaccine.
Explanation
This is a classic “bat found dead in the room” exam question. Rabies virus is especially common in bats, but is also found in dogs, cats, wolves, ferrets, raccoons, skunks, and foxes. On the exam (and in real life), give RIG and vaccine to anyone who was sleeping in the room, even if there is no evidence of a bite or scratch (except in rabies-free Hawaii).

Question 21

A 4-year-old boy presents with:

Fever
Ulcerations on his soft palate and buccal mucosa
Vesicles on his pharynx
Red maculopapules and vesicular rash on his hands and feet
What is the most likely etiology of his signs and symptoms?

Answer 21

Coxsackievirus
Explanation
Coxsackievirus is a common cause of hand-foot-and-mouth disease, especially coxsackievirus A16. In infants, the diaper area is commonly involved with the rash. In addition to coxsackievirus, other enteroviruses such as enterovirus Type 71 (EV-71) can cause this.

Question 22

How does late-onset group B streptococcal (GBS) infection present?

Answer 22

Bacteremia without a focus (50%) and meningitis (40%)
Explanation
Late-onset GBS disease occurs at a median onset of 27 days of life, with a range of 7 days to 3 months of age. Bacteremia without a focus is the most common presentation, with meningitis as the next most common. < 10% present with osteomyelitis (especially proximal humerus) and septic arthritis (e.g., hip, knee, ankle); cellulitis/adenitis is the least common manifestation.

Question 23

A 5-year-old girl presents with a 1-week history of a tender, left axillary lymph node after receiving a cat scratch to her left hand.

What is the name of the organism most likely responsible for her disease?

Answer 23

Bartonella henselae
Explanation
This is catscratch disease which is caused by Bartonella henselae. Treatment is supportive; the key is to avoid needing to incise and drain the lymph node because a persistent sinus tract will likely develop. Azithromycin has been shown to reduce the time for lymph node swelling to resolve, but spontaneous resolution usually occurs in 2–4 months without antibiotics.

Question 24

A 2-year-old day care attendee presents with:

Fever
Vomiting
Bloody diarrhea
New tonic-clonic seizure
Rectal prolapse
White blood cell count is elevated with a significant bandemia.

What is the most likely etiology for the diarrhea and the other findings?

Answer 24

Shigella
Explanation
Shigella is a common cause of diarrhea, especially in day care centers. Children 1–4 years of age have the highest incidence. Bloody diarrhea and seizures commonly occur; rectal prolapse is seen in 5–8% of cases. Bandemia is also very common. Most illnesses are self-limited, but antibiotics are recommended in severe cases and can shorten the disease’s course and limit its spread to others.

Question 25

A 13-year-old girl who lives on a turkey farm presents with:

Fever to 105.0°F (40.6°C)
Myalgias
Rigors
Pneumonia
Splenomegaly
What is the most likely etiology?

Answer 25

Answer
Chlamydia psittaci
Explanation
C. psittaci is found in psittacine (e.g., parrots, parakeets) and other birds and causes psittacosis (pneumonia and splenomegaly). With any pneumonia associated with poultry or pigeons, especially with splenomegaly, strongly suspect C. psittaci.

Differential: Histoplasma also causes pneumonia and splenomegaly; it is found in bird and bat droppings, but the question will generally mention geography (Ohio or Mississippi River Valleys).

Question 26

A 14-year-old boy from Hawaii presents with the following:

History of swimming in fresh-water lagoons
Fever
Conjunctival redness without exudates
Myalgias and headaches
Jaundice
Laboratory:

Creatinine 1.9 mg/dL
Bilirubin is disproportionately high compared to AST/ALT, which are each mildly elevated.
What is the most likely diagnosis

Answer 26

Leptospirosis
Explanation
Leptospirosis is a spirochetal disease that is transferred by contact with contaminated water or infected animals. Rats, dogs, and livestock are the most common vectors. Many patients have a biphasic illness (2 phases separated by 3–4 days of no fever). Diagnose with blood (acute phase) or urine cultures (immune phase), along with serum antibodies.

Question 27

Does treatment of nontyphoidal Salmonella gastroenteritis shorten the duration of the illness?

Answer 27

No
Explanation
Therapy for Salmonella gastroenteritis does not shorten the duration of illness, and it may prolong the carrier state. Only give antibiotic therapy for nontyphoidal Salmonella diarrhea to children < 3 months of age, those with hemoglobinopathies, and older children with immunocompromising conditions (e.g., HIV/AIDS, agammaglobulinemia, malignancy, Crohn’s).

Question 28

A mother develops chickenpox in the immediate perinatal period.
What time frame represents the highest case fatality rate if the infant develops neonatal varicella?

Answer 28

When the mother develops varicella lesions 5 days before to 2 days after delivery
Explanation
This is very important to remember: These infants are at highest risk for severe varicella-zoster virus (VZV) primary infection—a high case fatality rate! In this time frame, newborns are exposed to VZV from the mother; however, no protective varicella-specific IgG antibody is passed to them through the placenta. Administering varicella zoster immune globulin to the exposed infants may reduce risk of severe infection. In fact, some experts advise its use in all exposed newborns < 2 weeks old when the mother lacks immunity to varicella. Also remember: If the mother develops herpes zoster (a.k.a. shingles) at the time of delivery, that represents a reactivation of VZV. This means that the mother should have had antibodies to VZV that were transmitted to the fetus during late gestation, which should protect the infant against varicella.

Question 29

A 10-year-old boy from Ukraine with no immunization history presents with:

Sore throat
Hoarseness
Temperature 100.0°F (37.8°C)
Conjunctivitis
Gray-white pharyngeal membrane
What is the most likely diagnosis

Answer 29

Diphtheria
Explanation
Corynebacterium diphtheriae is the cause of diphtheria. Tonsillopharyngeal diphtheria is an upper respiratory infection with these findings (note the low fever). 10% of patients with diphtheria develop myocarditis, which typically occurs in the 1st week of infection.

Question 30

A 15-year-old girl presents with:

History of mild upper respiratory infection similar to a common cold
Persistent (> 2 weeks) cough that causes her to cough for long periods of time
No fever
Normal complete blood count (CBC)
What is the likely diagnosis

Answer 30

Pertussis
Explanation
You may have been thinking pertussis until the CBC was reported as normal—but in adolescents, the CBC usually is normal. (An elevated white blood cell count with an absolute lymphocytosis is generally only seen in infants and younger children.) This girl’s pertussis has advanced to the paroxysmal stage. Cough-variant asthma can present the same way.

Question 31

A 15-month-old girl received 1 dose of MMR at 10 months of age during a community-wide outbreak of measles.

Will this patient require 1 or 2 additional doses of MMR before 6 years of age?

Answer 31

2 additional doses
Explanation
MMR vaccine is routinely recommended at 12–15 months and 4–6 years of age. During an outbreak of measles, MMR vaccine may be administered to infants 6 months through 11 months of age. However, because of the presence of maternal antibody, seroconversion rates after MMR immunization are significantly lower in children immunized before 12 months of age when compared to those immunized after 12 months. Therefore, doses received prior to the 1st birthday should not count toward the recommended 2-dose series

Question 32

After multiple patients present with diarrhea, it appears that a community-wide outbreak is occurring. It is thought that the drinking water may be contaminated with an acid-fast organism.

What is the likely organism?

Answer 32

Cryptosporidium
Explanation
Suspect chlorine-resistant Cryptosporidium in a community-wide outbreak such as described in this scenario. Sources can include contaminated city water, as well as water parks and swimming pools. The diarrhea can be prolonged; however, it is most commonly self-limited in immunocompetent individuals who recover in a few days with only supportive care. Patients with immunosuppression (e.g., HIV) can have more severe/prolonged illness and may require antimicrobial treatment (nitazoxanide) for 2 or more weeks. Diagnose by doing a specific stool Cryptosporidium PCR or antigen test.

Question 33

A girl presents with chickenpox.

When are patients with chickenpox contagious

Answer 33

1–2 days prior to onset of the rash until all lesions are crusted over
Explanation
Children may return to school or day care when all the lesions are crusted over. Hospitalized patients who are exposed to chickenpox need to be placed in a negative-pressure isolation room if their hospitalization falls within the time frame of days 8−21 after exposure (up to 28 days after exposure if varicella-zoster immunoglobulin was administered).

Question 34

A 15-year-old boy with IV drug use history presents with:

Three positive viridans streptococci blood cultures
Fever
Positive rheumatoid factor (+RF)
What is the most likely diagnosis

Answer 34

Endocarditis
Explanation
Using the modified Duke criteria, this boy has 1 of the 2 major criteria (positive blood culture with viridans streptococci) and 3 of the 5 minor criteria (IV drug use, fever, +RF) for a diagnosis of endocarditis. In this case, 1 Duke major clinical criterion + 3 Duke minor clinical criteria meets the standard for “definite” endocarditis.

Question 35

An infant is suspected of neonatal sepsis and started on ampicillin and gentamicin.

Which of these medications requires dose adjustment because of age-related factors in renal function

Answer 35

Gentamicin
Explanation
Gentamicin is an aminoglycoside that is active against aerobic, gram-negative organisms. Dosing differs in neonates and young infants because of immaturity in renal function (decreased glomerular filtration rate and larger total body water composition compared to older children/adults). The kidneys are one of the primary routes of drug excretion, along with the liver. Major side effects include nephrotoxicity and ototoxicity

Question 36

A White adolescent boy presents with hyperpigmented, scaly lesions on his chest and back that worsen when he plays football in the hot sun.

What is the likely diagnosis?

Answer 36

Answer
Tinea versicolor
Explanation
Tinea (a.k.a. pityriasis) versicolor is due to Malassezia infection. Of the > 10 species identified, M. globosa, M. restricta, M. sympodialis, and M. furfur have been commonly cultured from pityriasis lesions. It is very common in adolescents, particularly if there is exposure to heat and moisture and occlusive clothing is being worn. Skin lesions can be hypo- or hyperpigmented scales, and scraping will show classic “spaghetti and meatball” organisms. Treat with topical selenium sulfide or topical azole; oral fluconazole or itraconazole can also be used.

Question 37

A 17-year-old girl with HIV learns that she is pregnant. Her most recent CD4 count was 780 cells/µL, and she has not been on anti-HIV medications. A repeat CD4 count is now 820 cells/µL.

Should she be started on anti-HIV medications?

Answer 37

Yes
Explanation
Current HIV therapy guidelines list pregnancy as a “definite” for starting anti-HIV medications as soon as possible, regardless of viral load or CD4 count. The risk of infection for an infant born to an HIV-positive mother who did not receive interventions to prevent transmission is about 25% in the U.S. Programs designed for the prevention of mother-to-child transmission can reduce the rate of transmission to < 1%.

Question 38

A 17-year-old presents with:

Low-grade fever
Cough
Wheezing
Negative cold agglutinins
What is the most likely etiology for this patient’s pneumonia?

Answer 38

Chlamydia pneumoniae
Explanation
Chlamydia (formerly Chlamydophila) pneumoniae causes community-acquired pneumonia in children > 5 years of age and adolescents. Bronchospasm is particularly prominent in respiratory infection caused by this pathogen. It can be treated with macrolides, including erythromycin or azithromycin; tetracyclines and fluoroquinolones are also effective.

Question 39

A 2-year-old African child from rural Chad presents with:

Fever
Paralysis that began in the proximal muscles of the thigh and has progressively involved more distal muscle groups
What is the most likely diagnosis?

Answer 39

Polio
Explanation
Polio has essentially been eliminated from the Western Hemisphere and developed countries; however, Afghanistan, Pakistan, and Nigeria have never interrupted its transmission. Polio can be differentiated from Guillain-Barré syndrome by the patterns of the spread of paralysis; with Guillain-Barré, the paralysis begins distally and spreads proximally in an ascending manner, the opposite of polio (descending paralysis).

Question 40

A woman is infected with parvovirus B19 while pregnant.

What serious complication do you worry about in this case?

Answer 40

Answer
Nonimmune hydrops fetalis
Explanation
Fortunately, most mothers who are infected with parvovirus B19 during pregnancy have infants without abnormalities. Most infections with parvovirus B19 are asymptomatic. However, there is a risk of nonimmune hydrops fetalis and possibly fetal loss (~ 2–6%).

Question 41

How does early-onset group B streptococcal (GBS) infection present in the newborn?

Answer 41

Septicemia (45%) and pneumonia (40%)
Explanation
Early-onset GBS infections occur at 0–7 days of age. Obstetric complications and prematurity are common factors associated with early-onset GBS disease. Meningitis is rare (< 10%) in this age group.

Question 42

A patient in the summertime from rural Connecticut presents with:

Fever
Headache
Leukopenia
Thrombocytopenia
Anemia
Elevated AST/ALT
What is the most likely diagnosis?

Answer 42

Anaplasmosis
Explanation
Human granulocytic anaplasmosis (HGA; due to Anaplasma phagocytophilum) is a tick-borne disease that predominates in the Northeast and Midwest. Classically, it presents with a pancytopenia and fever. A similar disease, human monocytic ehrlichiosis (HME; caused by Ehrlichia chaffeensis), occurs in Arkansas, Missouri, and Oklahoma. Connecticut should make you think about Lyme disease as well, but erythema migrans should be present.

Question 43

A 14-year-old boy presents with diarrhea. You learn that he has a pet iguana in the house.

What is the most likely cause of his diarrhea

Answer 43

Nontyphoidal Salmonella
Explanation
The main cause of Salmonella outbreaks is contaminated food, including frozen foods (especially chicken), milk, eggs, produce, and peanut butter; however, iguanas, baby chicks, frogs, turtles, and other exotic pets can also be sources of infection.

Question 44

A 6-month-old with β-thalassemia has fever; the blood culture is growing a gram-negative rod.

What organism should you suspect?

Answer 44

Yersinia enterocolitica
Explanation
Bacteremia with Y. enterocolitica is more common in children < 1 year of age and in older children with iron overload, especially those who are transfusion dependent (e.g., sickle cell disease, β-thalassemia, aplastic anemia).

Question 45

Amphotericin B causes renal losses of which 2 electrolytes?

Answer 45

Potassium and magnesium
Explanation
Amphotericin B is a polyene antifungal agent. While it remains an effective treatment for most systemic mycoses, amphotericin B has many side effects—these include fever, renal failure, phlebitis, and acidosis, as well as low potassium and magnesium. Always monitor serum potassium and magnesium levels during amphotericin B therapy.

Question 46

A 9-year-old presents with a history of travel to the Rocky Mountains for a camping trip this summer. He has had watery, smelly diarrhea for the last week with multiple episodes daily of flatulence. His mother says that he has been burping a lot and that it smells horrible, “like sulfur.”

What is the most likely diagnosis?

Answer 46

Giardiasis
Explanation
Giardia is the most common disease-causing intestinal parasite in the U.S. It also is the most frequently identified diarrheal agent in waterborne-associated infections. Acute symptoms are like those described here (“sulfuric belching” is common). Diagnose by checking for a Giardia-specific antigen in the stool.

Question 47

A 10-year-old boy presents with:

Sore throat
Headache
Fever
Cervical lymphadenopathy
Splenomegaly
What is the best way to test your suspected diagnosis?

Answer 47

Test for Epstein-Barr virus (EBV)–specific antibodies
Explanation
The patient most likely has EBV infection. Infectious mononucleosis is the most common clinical illness that explains these findings. Diagnosis is made by EBV-specific antibodies. If the IgM-viral capsid antigen is positive, the patient has acute primary EBV or a very recent-past EBV infection. If the EBV nuclear antigen is positive, the patient is convalescent or post-EBV.

Question 48

A child with cyanotic heart disease presents with new-onset headache and seizure. MRI shows a brain abscess.

Which organism is most likely responsible

Answer 48

Staphylococcus aureus
Explanation
S. aureus infections of the CNS (e.g., meningitis) are unusual, but children with cyanotic congenital heart disease have an increased risk of staphylococcal brain abscesses (especially in the setting of endocarditis and septic emboli).

Question 49

You are on a medical mission trip in rural Uganda and are visiting a new mother infected with HIV.

Do you recommend that she breastfeed her infant?

Answer 49

Yes
Explanation
In resource-limited settings, the WHO recommends that the HIV-infected mother exclusively breastfeeds for the first 6 months of her infant’s life and to continue breastfeeding for at least 12 months with the addition of complementary foods. In the U.S., where formula is safe, affordable, and readily available, breastfeeding is not recommended because suppressive maternal antiretroviral therapy significantly reduces but does not eliminate the risk of HIV transmission through breastfeeding.

Question 50

A 17-year-old presents with:

Pneumonia
Diarrhea
CNS symptoms (headache, delirium, and confusion)
What is the most likely etiology of this triad?

Answer 50

Legionella pneumophila
Explanation
L. pneumophila causes 80–90% of human Legionellae infections. L. pneumophila infection (legionellosis) is a multisystem disease, with the 3 findings listed here being the classic triad. It is commonly associated with outbreaks related to contaminated water towers or air-conditioning water units in buildings, hotels, cruise ships, and hospitals. Legionellae infections are rarely seen in children.

Question 51

A 17-year-old works in a pet store and spends most of his days cleaning debris from the fish tanks. He has had skin ulcerations on his right arm for several weeks that are unresponsive to cephalexin. Additionally, he was treated with clindamycin for methicillin-resistant Staphylococcus aureus without improvement.

What is the most likely etiology for his persistent skin ulcerations?

Answer 51

Answer
Mycobacterium marinum
Explanation
M. marinum is the “fish tank bacillus.” It causes nonhealing skin ulceration in people working around fish tanks. Often the lesions are along lymphatic channels. Treat with ethambutol + rifampin or clarithromycin + rifampin.

Question 52

A 6-year-old girl attending summer camp presents with:

Fever
Pharyngitis
Conjunctivitis
Rhinitis
Cervical adenitis
Multiple other camp attendees are similarly affected.

What is the likely etiology for her signs and symptoms?

Answer 52

Adenovirus
Explanation
Adenovirus can cause a pharyngoconjunctival fever, particularly during the summer months, and is commonly associated with outbreaks at swimming pools in summer camps. It can also cause epidemic keratoconjunctivitis—this occurs with conjunctivitis, painful corneal involvement, and preauricular lymph node enlargement.

Question 53

A 6-year-old boy develops bloody diarrhea, then has the following complications:

Acute kidney injury
Thrombocytopenia
Hemolytic anemia
What is the etiology of the initial diarrhea and the new findings?

Answer 53

E. coli O157:H7
Explanation
E. coli O157:H7 is responsible for hemolytic uremic syndrome, which has the classic triad of renal failure, thrombocytopenia with purpura, and hemolytic anemia. Do not treat the infectious diarrhea with antibiotics because it has not been shown to be beneficial; in fact, adverse events can occur. Common reservoirs for E. coli O157:H7 include undercooked beef, unpasteurized milk, or contaminated apple juice.

Question 54

You have diagnosed a patient with active tuberculosis.

What comorbid conditions should you consider before prescribing isoniazid as part of your treatment regimen?

Answer 54

Acute liver disease (of any etiology) and alcohol use
Explanation
Isoniazid (a.k.a. isonicotinic acid hydrazide [INH]) is metabolized in the liver. It induces components of the cytochrome P-450 system when combined with alcohol, thus increasing toxicity, and is contraindicated in patients with acute liver disease. In all patients on INH, regardless of age, monitor monthly for signs and symptoms of liver toxicity. Laboratory testing is indicated if signs or symptoms develop. INH carries an FDA black box warning regarding the risk of hepatitis.

Question 55

A 12-year-old boy who lives in Arizona loves to hunt prairie dogs and skins them with his old hunting knife. He presents with a 3-day history of fever, chills, headache, and a painful, swollen right inguinal lymph node.

What organism do you suspect?

Answer 55

Yersinia pestis
Explanation
Y. pestis causes plague and has a high mortality. The reservoir is wild rodents; infection is transmitted by fleas or by direct contact (e.g., through skinning animals). The bubonic form of plague causes painful, swollen lymph nodes (buboes). If not treated, it can lead to the septicemic form, characterized by hypotension, respiratory distress, organ failure, and death. The bubonic type can also lead to a pneumonic form (bioterrorism related). Most human cases occur in New Mexico, Arizona, California, or Colorado.

Question 56

A 17-year-old homeless boy with history of current IV drug use (heroin) and multiple sexual partners (both male and female) presents with:

Fever
Lymphadenopathy
Pharyngitis
Erythematous maculopapular rash on the face, trunk, and extremities (including palms and soles)
Mucocutaneous ulcers of the mouth and genitals
Myalgias/arthralgias
Negative rapid mono and strep tests
Negative RPR
What is the most likely diagnosis?

Answer 56

Acute retroviral HIV syndrome
Explanation
This constellation of signs and symptoms in a high-risk person is consistent with acute retroviral HIV syndrome. This typically occurs 2–4 weeks after the initial infection and lasts 1–2 weeks. Diagnose HIV acutely with an HIV antibody/p24 screen; if positive, send for an HIV RNA PCR (viral load).

Question 57

A 13-year-old girl has a staple injury (clean, minor wound). She has had 7 immunizations for tetanus, and her last immunization was 7 years ago.

What do you recommend for her in regards to immunization for tetanus?

Answer 57

No immunization
Explanation
If the patient has had ≥ 3 immunizations in the past, and it has been < 10 years since her last immunization, then she does not require further tetanus immunization.

Question 58

A newborn of a mother who recently immigrated from Albania presents at birth with:

Petechiae and purpura on the face, trunk, and extremities
Hepatosplenomegaly
Hemolytic anemia
Patent ductus arteriosus (PDA) without pulmonary artery stenosis
Cataracts with microphthalmia
Radiolucencies in the metaphyseal long bones
What is the most likely diagnosis?

Answer 58

Congenital rubella syndrome
Explanation
Rubella was declared eliminated from the U.S. by 2004. By 2015, it was eliminated from the Americas. Since elimination, < 10 people in the U.S. are reported as having rubella each year. Since 2012, all rubella cases had evidence that they were infected while outside the U.S. It continues to be endemic in many areas of the world.

This infant has petechiae and purpura consistent with the “blueberry muffin” baby (as seen in congenital cytomegalovirus), but she also has a PDA and cataracts, which are classically seen in congenital rubella syndrome. Most likely, the mother was infected in the 1st trimester.

Question 59

An unimmunized child presents with buccal cellulitis (full thickness palpable on both sides of the cheek and purplish in color) due to Haemophilus influenzae.

What do you expect to find systemically?

Answer 59

Bacteremia
Explanation
Patients with buccal cellulitis due to H. influenzae are almost always bacteremic. These children should always be admitted and placed on IV antibiotics.

Question 60

An 8-day-old infant presents with macules on the scalp that have become vesicular on a red base in the last few hours. They appear to be at the site of the infant’s fetal scalp monitor. The mother wonders if the site is infected. She has no history of infection during her pregnancy and is not known to be colonized with methicillin-resistant Staphylococcus aureus.

What is the most likely diagnosis?

Answer 60

Neonatal herpes simplex virus (HSV) infection
Explanation
Neonatal HSV infections are localized to the skin, eye, mouth region in ∼ 45% of cases, 30% in the CNS only, and 25% are disseminated. Commonly (60–80%), the mother has no clinical history of herpes infection. Fetal scalp monitor sites are a common location, as well as eye margins, circumcision sites, and the presenting part. These infections are commonly misdiagnosed as staphylococcal. Never overlook HSV as a possibility in a neonate with a vesicular-looking lesion! Neonatal HSV infection (especially when disseminated) is often severe, with high mortality and severe CNS sequelae (even with appropriate antiviral therapy).

Question 61

A 16-month-old girl presents with:

Thick, purulent nasal discharge
Low-grade fever
Decreased feeding
Abdominal pain
What is the most likely diagnosis?

Answer 61

Streptococcosis
Explanation
Streptococcus pyogenes is the only member of the group A β-hemolytic streptococci (GABHS). Toddlers with GABHS upper respiratory infections do not present with pharyngitis, but rather with thick, purulent nasal discharge, low-grade fever, and decreased feeding (known as streptococcosis).

Question 62

A 5-year-old presents for her 1st influenza vaccine.

How many doses should she receive?

Answer 62

2 doses, 1 month apart
Explanation
For children < 9 years of age who have never been vaccinated for the flu, this vaccination schedule will produce adequate antibody levels. Thereafter, they receive 1 flu vaccine dose annually.

Question 63

A 13-year-old from Missouri presents with:

Interstitial pneumonia
Palate ulcers
Splenomegaly
What is the most likely diagnosis?

Answer 63

Histoplasmosis
Explanation
Histoplasmosis is endemic to the Mississippi and Ohio River valleys and is associated with bird (especially chicken) and bat droppings. Remember that histoplasmosis has a pneumonia with splenomegaly similar to Chlamydia psittaci infection, but histoplasmosis also commonly has palate ulcers

Question 64

A 13-year-old girl steps on a dirty, rusty nail. She has had 6 previous tetanus immunizations, with her last being a DTaP immunization 6 years ago.

What do you recommend for her today?

Answer 64

Tdap immunization
Explanation
The girl has had ≥ 3 tetanus immunizations in the past, so she does not require immunoglobulin for this dirty wound. However, her last tetanus immunization was 6 years ago and was a DTaP. She has not had a Tdap booster that includes pertussis, so she needs this today. If her last immunization 6 years ago had been a Tdap, then today she would be given a Td. (Only 1 Tdap per lifetime is recommended at present, the exception being that maternal Tdap is recommended for each pregnancy.)

Question 65

A bat is found in the room of a sleeping 2-year-old boy. His parents like to keep the windows cracked open to enjoy the cool Hawaiian breeze.

Should he be given rabies prophylaxis?

Answer 65

No
Explanation
In areas where rabies is found, you would always provide rabies postexposure prophylaxis if you found a bat in the room of a sleeping child; however, Hawaii is the only state in the U.S. that is rabies free!

Question 66

What is the most common organism to cause infection in cat bites?

Answer 66

Pasteurella multocida
Explanation
P. multocida classically causes rapidly progressing cellulitis within 24 hours of the bite, often accompanied by fever and regional lymphadenopathy. It is the #1 cause of infection in a cat bite, followed by Staphylococcus aureus. Give antibiotics for all cat bites—cat teeth tend to cause deep puncture wounds. Amoxicillin/clavulanate is the drug of choice.

Question 67

An 8-month-old presents with an initial history of fever for 4 days; the child was seen 2 days ago for a febrile seizure. The fever broke today and a rash developed, which is why the mother returned with the child. The rash is macular-to-maculopapular and mainly on the trunk and extremities.

What is the diagnosis? What is the organism responsible?

Answer 67

Roseola infantum (a.k.a. exanthema subitum, roseola infantum, sixth disease); human herpesvirus 6 (HHV-6)
Explanation
By 3 years of age, nearly all children are infected with HHV-6, which can cause roseola. Roseola classically presents as described here, with fever for 3–5 days followed by the abrupt cessation of the fever and development of a macular-to-maculopapular rash. Seizures occur in ~ 10% during the febrile stage. Human herpesvirus 7 is a less frequent cause of roseola.

Question 68

A newborn presents with:

Microcephaly
Hydrocephalus
Hepatosplenomegaly
Maculopapular rash
Retinochoroiditis
Cerebral calcifications (widespread)
What is the most likely diagnosis?

Answer 68

Congenital toxoplasmosis
Explanation
Toxoplasmosis during pregnancy can be very problematic. The risk of congenital infection to the fetus increases when the disease is acquired later in pregnancy; however, the severity of disease is inverse to this. Infants infected early in pregnancy are more likely to be severely affected, like the child in this scenario. The classic triad of chorioretinitis, hydrocephalus, and cerebral calcifications is highly suggestive of congenital toxoplasmosis.

Remember—diffuse calcifications in the parenchyma are usually from toxoplasmosis. If calcifications “CircuMVent” the ventricles (i.e., are periventricular), the cause is almost always CMV, not toxoplasmosis!

Question 69

A 10-year-old boy presents with:

Severe sore throat
Temp 102.0°F (38.9°C)
Tender cervical lymphadenopathy
Exudative tonsils
Rhinorrhea
Which procedure should you perform: a rapid strep test, strep culture, both, or neither?

Answer 69

Neither
Explanation
Presence of cough, rhinorrhea, or other symptoms of upper respiratory infection with sore throat is more suggestive of a viral etiology than streptococcal infection. Do not check for group A Streptococcus if URI symptoms are present. If he did not have rhinorrhea, then everything else fits for strep infection.

Question 70

A college freshman presents with:

Cough
Coryza
Conjunctivitis
Fever
Malaise
Splenomegaly
Macular rash that began on the hairline and now has spread to the trunk
What is the most likely diagnosis?

Answer 70

Measles (rubeola)
Explanation
Measles is still occurring in scattered outbreaks around the U.S., including in colleges. The “3 Cs”—cough, coryza, and conjunctivitis—are classic with the rash. Koplik spots, which are bluish-white spots on an erythematous base and appear on the buccal mucosa 2–3 days before the rash appears, are pathognomonic. Splenomegaly and lymphadenopathy are also common.

Question 71

A 17-year-old boy presents with submandibular swelling and fever. He is diagnosed with mumps.

Which genitourinary complication occurs commonly in males with mumps?

Answer 71

Epididymoorchitis
Explanation
In postpubertal boys with mumps, 15–35% get epididymoorchitis. It is less common in prepubertal boys. Sterility after infection is very rare. Oophoritis occurs in ~ 5–7% of postpubertal girls. Other significant complications of mumps include:
Mastitis (described in 31% of adolescent girls in a 1956–1957 outbreak)
Meningitis (CSF pleocytosis is common [> 50%]; symptomatic is less common [10%]; usually self-limited)
Temporary deafness (in 1 study, 4% of those affected)

Question 72

Two children, 9 months and 3 years of age, present for evaluation 24 hours after an outbreak of measles was identified. The outbreak affected infants and children of all ages. The 9-month-old has not received MMR vaccine. The 3-year-old has received 1 dose at age 15 months of age.

Is postexposure prophylaxis with MMR indicated in neither, one, or both of the children?

Answer 72

Both
Explanation
During an outbreak, measles vaccine given to susceptible individuals within 72 hours of exposure provides protection or disease modification in most cases. Measles vaccine should be considered in all exposed individuals who are eligible to receive the vaccine (those > 12 months of age) and who have not been vaccinated or who have received only 1 dose of vaccine. In addition, MMR vaccine may be administered to infants 6 months through 11 months of age in an outbreak. However, seroconversion rates after MMR immunization are significantly lower in children immunized before 12 months of age. Therefore, any dose received before 12 months of age should not count toward the recommended 2-dose series.

Question 73

A 3-year-old presents with:

Fever
“Slapped cheek” rash on the face
A lattice (or lace)-like rash on the arms and legs that is more prominent in sunlight or after a warm bath
What is the likely etiology of these signs and symptoms?

Answer 73

Parvovirus B19
Explanation
Parvovirus B19 is responsible for this classic presentation of erythema infectiosum (a.k.a. fifth disease). Once the rash appears, the child is no longer infectious. Adults, especially women, commonly get polyarthritis affecting small joints, particularly of the hand. Children less often (< 10%) develop arthritis, usually of the knee joint.

Question 74

An HIV-infected 2-year-old boy with recurrent pneumonia and failure to thrive was brought to the emergency department for:

Severe respiratory distress
Hypoxemia
Fever
Lymphopenia
CXR with diffuse infiltrates
Bronchoalveolar lavage positive for silver-staining organism
What is the most likely diagnosis?

Answer 74

Pneumocystis pneumonia (PCP)
Explanation
PCP is caused by Pneumocystis jiroveci (formerly Pneumocystis carinii), one of the more common pneumonia pathogens diagnosed in HIV-infected patients. Methenamine silver, toluidine blue O, calcofluor white, and fluorescein-conjugated monoclonal antibody are the most useful stains to identify the thick-walled cysts of P. jiroveci.

Question 75

A newborn presents with:

Intrauterine growth restriction
Hepatosplenomegaly
Jaundice
Thrombocytopenia
Petechia/purpura
Microcephaly
Cerebral atrophy
Chorioretinitis
Periventricular intracerebral calcifications
What is the most likely etiology of these signs and symptoms?

Answer 75

Congenital cytomegalovirus (CMV) infection
Explanation
Congenital CMV infection occurs in ~ 1% of all newborns in the U.S. What determines the severity of the infection is whether or not the mother has IgG antibodies to CMV. In the case of maternal primary CMV infection during pregnancy, there is an increased risk of this congenital syndrome occurring with dire consequences. This child has the most severe form of congenital CMV infection: cytomegalic inclusion disease. It can resemble toxoplasmosis; however, remember that the cerebral calcifications are periventricular (they CircuMVent the ventricles) in CMV. In toxoplasmosis, they are scattered throughout the cerebrum. Congenital rubella can present similarly, with the petechial/purpuric “blueberry muffin-like” rash.

Question 76

A 5-year-old boy from rural Arkansas presents with:

Fever to 102.0° F (38.9° C)
Swollen lymph node in his right inguinal area
What is the most likely diagnosis?

Answer 76

Tularemia (a.k.a. rabbit fever)
Explanation
On exams, if you see a child from Arkansas (or Missouri/Oklahoma) with a swollen lymph node and fever, think tularemia, which is caused by Francisella tularensis. This is especially true if the patient is someone who hunts, traps, or handles rabbits. Treat with gentamicin or streptomycin for 10 days.

Question 77

A 3-year-old girl presents with:

Painful rectal area
Bright red, sharply demarcated rash that is very painful and itchy
What is the likely diagnosis?

Answer 77

Perianal group A streptococcal cellulitis
Explanation
Perianal group A streptococcal dermatitis/perirectal cellulitis is a brightly erythematous, sharply demarcated rash that is very painful and often itchy. It most commonly occurs in children between 6 months and 10 years of age.

Question 78

The use of ointment in a newborn’s eyes is useful for preventing which infection(s): gonorrhea, Chlamydia, or both?

Answer 78

Gonorrhea
Explanation
Contrary to popular belief, the use of eye prophylaxis is only beneficial in preventing gonorrheal infection; it does not prevent Chlamydia trachomatis infection.

Question 79

A child with fever and purpura is examined for an hour. It is later determined that the child has meningococcemia.

Should the primary care physician examining a child with meningococcemia receive rifampin or ciprofloxacin prophylaxis?

Answer 79

No
Explanation
Health care workers should only take prophylaxis for meningococcus if they have close, intimate contact with oral secretions, such as with intubation or mouth-to-mouth resuscitation

Question 80

A child presents with mild antibiotic-associated colitis caused by Clostridioides (formerly Clostridium) difficile. She has a fever; labs indicate normal white blood cell and renal function. You treat her with oral metronidazole and her colitis resolves. She returns in 2 weeks with a recurrence.

What do you recommend for therapy now?

Answer 80

Oral metronidazole or oral vancomycin
Explanation
Recurrences of C. difficile infections occur in ∼ 25% (ranges 12–33%) of patients. Treat the 1st recurrence with metronidazole if the disease remains mild to moderate. Oral vancomycin is also an appropriate choice in this case. Oral vancomycin is recommended if initial infection or 1st recurrence is considered severe. Do not use metronidazole past the 1st recurrence. Treat 2nd or subsequent recurrences with oral vancomycin in a prolonged, tapered regimen.

Question 81

A patient from North Carolina presents with:

Fever
Headache
Arthralgias
Maculopapular rash on the extremities that has become more petechial
Serum sodium is 128 mg/dL.
Platelet count is 110,000/µL.
What is the most likely diagnosis?

Answer 81

Answer
Rocky Mountain spotted fever (RMSF)
Explanation
This is the classic scenario for RMSF, a tick-borne disease caused by Rickettsia rickettsii. It is mainly found in the mid-Atlantic states. The rash (which is absent in ∼ 20% of patients) begins at the ankles and wrists and then spreads within hours to the trunk, palms, and soles, progressing from maculopapular to petechial to purpuric. This disease has a 3% mortality rate. Treat with doxycycline.

Question 82

A child presents with a history of an itchy bottom. The mother reports that she thought she saw some “rice” around the child’s anus.

What is the most likely diagnosis?

Answer 82

Pinworms
Explanation
Pinworm (Enterobius vermicularis) infection is very common. Pregnant female worms travel out of the anus at night, leaving a trail of eggs on the surface of the skin. Diagnose by visualization of worms in the perianal region (they look like rice or small strands of spaghetti) or use the clear adhesive (Scotch) tape test to collect eggs laid by the female worm during the night. Know that reinfection is common, as is autoinoculation.

Question 83

What is the treatment of choice for a group B Streptococcus (GBS) infection?

Answer 83

Ampicillin + gentamicin, then penicillin G
Explanation
Ampicillin and gentamicin are started initially. Gentamicin is synergistic with ampicillin, and lowers the GBS bacterial load faster than ampicillin alone.

When GBS is confirmed, treat with IV penicillin G alone (or ampicillin) for:
10 days for pneumonia or bacteremia
14–21 days minimum for meningitis (14 days is sufficient for uncomplicated meningitis; gentamicin is often used until CSF cultures are sterile.)
3–4 weeks for septic arthritis or osteomyelitis

Question 84

A 15-year-old who lives on a farm and loves to eat chitterlings presents with an appendicitis-like syndrome.

What organism is most likely responsible if this is not appendicitis?

Answer 84

Yersinia pseudotuberculosis or Yersinia enterocolitica
Explanation
Y. pseudotuberculosis or Y. enterocolitica can each cause pseudoappendicitis syndrome, especially in older children and adolescents. This presents clinically just like appendicitis, but at the time of surgery, the appendix appears normal with inflammation of the terminal ileum and mesenteric lymph nodes.

Y. enterocolitica is transmitted by ingestion or handling of raw/undercooked pork products (especially chitterlings, which are made from pig small intestines), contaminated water, or direct/indirect contact with animals.

Question 85

A 10-year-old steps on a nail that goes through her tennis shoe.

What organism is most likely responsible if cellulitis (or another infection) develops?

Answer 85

Pseudomonas aeruginosa
Explanation
Consider P. aeruginosa in osteochondritis/osteomyelitis of the foot following a nail-puncture wound (especially if through a tennis shoe). It is also commonly the cause of endocarditis in IV drug users, bacteremia in burn patients, and chronic suppurative otitis externa (can be especially severe in patients with diabetes).

Question 86

A 2-month-old born vaginally presents with:

No fever
Staccato cough
CXR evidence of pneumonia
What is the most likely etiology of the infant’s pneumonia?

Answer 86

Chlamydia trachomatis
Explanation
C. trachomatis is commonly responsible for neonatal pneumonia in the first 4 months of life; 10–20% of newborns develop infection if born through a birth canal that is infected with this pathogen. Classically, the cough is described as a persistent staccato cough without fever.

Question 87

An unimmunized 3-year-old presents with:

Fever to 104.0°F (40.0°C)
Dysphagia
Drooling
She also is leaning forward with her neck hyperextended and chin thrust forward.

What is the likely diagnosis?

Answer 87

Epiglottitis
Explanation
Epiglottitis is rare today because of the widespread use of the Haemophilus influenzae Type b (Hib) vaccine, but it still occurs on occasion (especially in the unimmunized). The epiglottis is classically described as “cherry red.” It is important to keep the child comfortable and not upset her by trying to examine the oropharynx; you are likely to cause airway obstruction.

Question 88

Who is at greater risk to develop neuroinvasive disease from West Nile virus (WNV)—a 10-year-old girl, or her 65-year-old grandmother?

Answer 88

The grandmother is at greater risk for CNS disease.
Explanation
The majority of infections from WNV are asymptomatic with approximately 20% of people developing a self-limited febrile flu-like illness. The risk of neuroinvasive illness increases with age, and is highest among adults > 60 years of age.

Question 89

An adolescent who recently emigrated from sub-Saharan Africa presents with:

Low-grade fever
Postauricular lymphadenopathy
Headache
Sore throat
Macular rash on the face that has spread caudally to the neck and trunk
What is the most likely diagnosis?

Answer 89

Rubella (German measles)
Explanation
Rubella has been eliminated (no endemic transmission for 12 or more months) from the U.S. since 2004. In 2015, it was eliminated from the Americas. Since elimination, < 10 people in the U.S. are reported as having rubella each year. Since 2012, all rubella cases had evidence that they were infected while outside the U.S. It continues to be endemic in many areas of the world.

In older children and adolescents, rubella presents with a prodrome of low-grade fever, malaise, headache, and sore throat for a 1- to 5-day period before the rash appears. The rash can be very fleeting and changes appearance (fading) over time. It usually begins as pink-red macules on the face that spread quickly to the neck, trunk, arms, and finally the legs. Generally, the rash is gone from the face by the time it reaches the legs.

Question 90

A 4-year-old presents with presumed bacterial meningitis.

What are the drugs of choice for empiric therapy?

Answer 90

Ceftriaxone (or cefotaxime) and vancomycin
Explanation
Because of the increased rate of penicillin- and cephalosporin-resistant Streptococcus pneumoniae isolates causing invasive disease, vancomycin has been added to the standard therapy of 3rd generation cephalosporins (ceftriaxone or cefotaxime) for children > 3 months of age suspected of having bacterial meningitis. This combination should be used empirically in all such patients. Antibiotics can be modified once you obtain the results of susceptibility testing.

Question 91

What is the main side effect of zidovudine (ZDV)?

Answer 91

Bone marrow suppression
Explanation
ZDV is a nucleoside reverse transcriptase inhibitor. While it is rarely used for treatment in adults, there are still some uses for ZDV—it can be given intravenously to HIV+ pregnant patients with viral loads > 1000 copies during labor, and given orally to HIV-exposed newborns as prophylaxis after birth. It is well tolerated at currently used doses, but can cause bone marrow suppression (e.g., mostly anemia, but also granulocytopenia, thrombocytopenia). It also less commonly causes myopathy.

Question 92

A 7-year-old girl comes into your office to get her flu vaccine. She is allergic to eggs.

Can you give her a flu vaccine, or do you have to refer her to an allergist?

Answer 92

You can give her a flu vaccine.
Explanation
With the exception of few (cell- or recombinant-based) products, influenza vaccines contain trace amounts of egg proteins. Data have shown that these egg-based vaccine products can be safely given to people with an egg allergy, including urticaria, swelling or angioedema, respiratory distress, light headedness or repeated vomiting. According to the Joint Task Force on Practice Parameters, the special precautions regarding medical setting and waiting periods after the administration of egg-based flu vaccine to these egg-allergic recipients are no longer warranted beyond those recommended for any vaccine; i.e., waiting 15 minutes to avoid hurting themselves if they faint. It is recommended that anyone with a history of severe allergic reaction to a previous dose of influenza vaccine, regardless of suspected offending component, should be referred to an allergist to determine whether future doses are appropriate.

Question 93

Occurs in infants < 1 month of age
Maternal amnionitis
Brown-staining of the amniotic fluid
Preterm birth
Pneumonia and septicemia
Erythematous rash with papules, known as “granulomatosis infantisepticum”
What organism is associated with these findings?

Answer 93

Listeria monocytogenes
Explanation
L. monocytogenes is a gram-positive rod. It causes infections in settings of decreased cellular immunity such as solid organ transplants, immunodeficiency, lymphoma, and leukemia; it is also seen in neonates and pregnant women. In neonates, it is associated with the factors listed here. Neonates generally get the infection postnatally from their colonized mothers. Environmental sources of the organism include sheep, goats, other livestock, and poultry. Infection can also occur from direct contact with goat cheese, uncooked hot dogs, tofu, or contaminated vegetables.