Infectious Disease Flashcards
Specify which bugs are associated with UTIs and what empirical antibiotic should be used while waiting for culture results
Escherichia coli
Treatment: TMP-SMX, nitrofurantoin, amoxicillin, quinolones
Specify which bugs are associated with bronchitis and what empirical antibiotic should be used while waiting for culture results
Virus, Haemophilus influenzae, Moraxella spp.
Treatment: Usually no benefit from antibiotics. May consider macrolides or doxycycline
Specify which bugs are associated with pneumonia (classic vs atypical) and what empirical antibiotic should be used while waiting for culture results
Classic: Streptococcus pneumoniae, H. influenzae
- treatment: Third-generation cephalosporin, azithromycin
Atypical: Mycoplasma, Chlamydia spp.
- treatment: Macrolide antibiotic, doxycycline
Specify which bugs are associated with osteomyelitis and what empirical antibiotic should be used while waiting for culture results
Staphylococcus aureus, Salmonella spp.
Treatment: Oxacillin, cefazolin, vancomycin
Specify which bugs are associated with cellulitis and what empirical antibiotic should be used while waiting for culture results
Streptococci, staphylococci
Treatment: Cephalexin or dicloxacillin. TMP-SMX, doxycycline, or clindamycin are often used as first-line agents because of the emergence of MRSA
Specify which bugs are associated with meningitis (child) and what empirical antibiotic should be used while waiting for culture results
Streptococci B, E. coli, Listeria spp.
Treatment: Ampicillin + aminoglycoside (usually gentamicin); an expanded spectrum third-generation cephalosporin (cefotaxime) should be added if a gram-negative organism is suspected
Specify which bugs are associated with meningitis (child/adult) and what empirical antibiotic should be used while waiting for culture results
S. pneumoniae, Neisseria meningitidis*
Treatment: Cefotaxime or ceftriaxone + vancomycin
Specify which bugs are associated with endocarditis (native vs prosthetic valve) and what empirical antibiotic should be used while waiting for culture results
Endocarditis (native valve) - Staphylococci, streptococci
- Treatment: antistaphylococcal penicillin (ex: Oxacillin, nafcillin) or vancomycin if allergic to penicillin + aminoglycoside
Endocarditis (prosthetic valve) - Numerous different organisms
- Treatment: Vancomycin + gentamicin + cefepime or a carbapenem
Specify which bugs are associated with sepsis and what empirical antibiotic should be used while waiting for culture results
Gram-negative organisms, streptococci, staphylococci
Treatment: Third-generation penicillin/cephalosporin + aminoglycoside, or imipenem
Specify which 3 bugs are associated with septic arthritis and what empirical antibiotics should be used while waiting for culture results
S. aureus -> Vancomycin
Gram negative bacilli -> Ceftazidime or ceftriaxone
Gonococci -> Ceftriaxone, ciprofloxacin, or spectinomycin
Specify which empirical antibiotic should be used for Streptococcus A or B while waiting for culture results
1st line: Penicillin, cefazolin
Alternative(s): Erythromycin
Specify which empirical antibiotic should be used for S. pneumoniae while waiting for culture results
1st line: Third-generation cephalosporin + vancomycin
Alternative(s): Fluoroquinolone
Specify which empirical antibiotic should be used for Enterococcus while waiting for culture results
1st line: Penicillin or ampicillin + aminoglycoside
Alternative(s): Vancomycin + aminoglycoside
Specify which empirical antibiotic should be used for Staphylococcus aureus while waiting for culture results
1st line: Anti-staphylococcus penicillin (e.g., methicillin)
Alternative(s): Vancomycin, TMP-SMX, doxycycline, clindamycin, or linezolid for MRSA
Specify which empirical antibiotic should be used for Gonococcus while waiting for culture results
1st line: Ceftriaxone
Alternative(s): Cefixime or high-dose azithromycin followed by test of cure in 1 week
Specify which empirical antibiotic should be used for Meningococcus while waiting for culture results
1st line: Cefotaxime or ceftriaxone
Alternative(s): Chloramphenicol or penicillin G if proven to be penicillin susceptible
Specify which empirical antibiotic should be used for Haemophilus while waiting for culture results
1st line: Second- or third-generation cephalosporin
Alternative(s): Amoxicillin
Specify which empirical antibiotic should be used for Pseudomonas while waiting for culture results
1st line: Antipseudomonal penicillin (ticarcillin, piperacillin) +/- ß lactamase inhibitor (clavulanate, tazobactam)
Alternative(s): Ceftazidime, cefepime, aztreonam, imipenem, ciprofloxacin
Specify which empirical antibiotic should be used for Bacteroides while waiting for culture results
1st line: Metronidazole Alternative(s): Clindamycin
Specify which empirical antibiotic should be used for Mycoplasma while waiting for culture results
1st line: Erythromycin, azithromycin
Alternative(s): Doxycycline
Specify which empirical antibiotic should be used for Treponema pallidum while waiting for culture results
1st line: Penicillin
Alternative(s): Doxycycline
Specify which empirical antibiotic should be used for Chlamydia while waiting for culture results
1st line: Doxycycline, azithromycin
Alternative(s): Erythromycin, ofloxacin
Specify which empirical antibiotic should be used for Lyme disease (Borrelia spp.) while waiting for culture results
1st line: Cefuroxime, doxycycline, amoxicillin
Alternative(s): Erythromycin
Specify what a Gram stain of Blue/purple color most likely represents.
Gram-positive organism
Specify what a Gram stain of Red color most likely represents.
Gram-negative organism
Specify what a Gram stain of Gram-positive cocci in chains most likely represents.
Streptococci
Specify what a Gram stain of Gram-positive cocci in clusters most likely represents.
Staphylococci
Specify what a Gram stain of Gram-positive cocci in pairs (diplococci) most likely represents.
Streptococcus pneumoniae
Specify what a Gram stain of Gram-negative coccobacilli (small rods) most likely represents.
Haemophilus sp.
Specify what a Gram stain of Gram-negative diplococci most likely represents. 2
Neisseria sp. (sexually transmitted disease, septic arthritis, meningitis)
Moraxella sp. (lungs, sinusitis)
Specify what a Gram stain of Plump gram-negative rod with thick capsule (mucoid appearance) most likely represents.
Klebsiella sp.
Specify what a Gram stain of Gram-positive rods that form spores most likely represents. 2
Clostridium sp.
Bacillus sp.
Specify what a Gram stain of Pseudohyphae most likely represents.
Candida sp.
Specify what a Gram stain of Acid-fast organisms most likely represents. 2
Mycobacterium (usually M. tuberculosis)
Nocardia sp.
Specify what a Gram stain of Gram-positive with sulfur granules most likely represents.
Actinomyces sp. (PID in patients with IUDs; rare cause of neck mass/cervical adenitis)
Specify what a Gram stain of Silver-staining most likely represents.
Pneumocystis jiroveci and cat-scratch disease
Specify what a Gram stain of Positive India ink preparation (thick capsule) most likely represents.
Cryptococcus neoformans
Specify what a Gram stain of Spirochete most likely represents. 3
Treponema sp., Leptospira sp. (both seen only on dark-field microscopy)
Borrelia sp. (seen on regular light microscope)
What is the gold standard for diagnosis of pneumonia?
Sputum culture - obtain the culture before starting antibiotics, although many physicians treat empirically without culture in routine cases.
Obtain blood cultures as well because bacteremia is common with pneumonia.
What is the most common cause of pneumonia?
How does it classically present?
Bonus: How should you diagnose + treat this?
Streptococcus pneumoniae.
Presentation: rapid onset of rigors 1-2 days of URI symptoms (sore throat, runny nose, dry cough), followed by fever, pleurisy, and productive cough (yellowish-green or rust-colored from blood)
Diagnose: CXR - lobar consolidation, CBC - elevated WBC with large PMN%
Treatment:
- macrolide (e.g., azithromycin, clarithromycin)
- doxycycline
- third-generation cephalosporin + macrolide or doxycycline
- fluoroquinolone that provides atypical coverage (e.g., levofloxacin, moxifloxacin).
What is the best prevention against S. pneumoniae?
In which patient populations is this most important in?
Vaccination!
Give pneumococcal vaccine to:
- all children as well as adult patients over 65 years old
- splenectomized patients
- patients with sickle-cell disease (who have autosplenectomy) or splenic dysfunction
- immunocompromised patients (HIV, malignancy, organ transplant)
- patients with chronic disease (e.g., diabetes, cardiac disease, asthma and other pulmonary disease, renal disease, liver disease, or tobacco use)
How do you recognize and treat Haemophilus influenzae pneumonia?
How common is it?
How is it diagnosed and treated?
H. influenzae is now uncommon in children because of vaccination, but is still an important cause
of pneumonia in older adults and in those with underlying lung disease such as COPD
Often it resembles pneumococcal pneumonia clinically, but look for gram-negative coccobacilli on sputum Gram stain.
Treat with amoxicillin or a second- or third-generation cephalosporin.
Describe the hallmarks of Staphylococcus aureus pneumonia.
In which patient populations (4) does it tend to affect the most?
S. aureus tends to cause
- hospital-acquired (nosocomial) pneumonia
- pneumonia in patients with cystic fibrosis (along with Pseudomonas sp.)
- patients who abuse IV drugs
- patients with chronic granulomatous disease (look for recurrent lung abscesses).
Empyema and lung abscesses are relatively common with S. aureus pneumonia.
In what clinical situations do you tend to see gram-negative pneumonias?
Which 3 are the most common?
How should you treat these patients?
- Pseudomonas infection is classically associated with cystic fibrosis
- Klebsiella infection may be found in patients who are homeless and/or suffer from alcoholism (watch for classic description of currant jelly sputum)
- Enteric gram-negative organisms (e.g., Escherichia coli) are associated with aspiration, neutropenia, and hospital-acquired pneumonia.
High mortality rate because often patients are already in poor health and the severity of the pneumonia (abscesses are common).
Treat empirically with an antipseudomonal penicillin (e.g., ticarcillin, piperacillin) +/- beta lactamase inhibitor (e.g., clavulanate, tazobactam).
- Alternatives include ceftazidime or ciprofloxacin.
How do you recognize Mycoplasma pneumonia?
In which patients is it most common?
How is it diagnosed and treated?
cause of atypical pneumonia; most common in adolescents and young adults (the classic patient is a college student or soldier who lives in a dormitory/barracks and has sick contacts)
sx: has a long prodrome with gradual worsening of malaise, headaches, dry, nonproductive cough, and sore throat; the fever tends to be low-grade
dx:
- CXR: patchy, diffuse bronchopneumonia and classically looks impressive, although the patient often does not feel that bad
- Positive cold-agglutinin antibody titers, which may cause hemolysis or anemia (compared to chlamydial pneumonia, which has negative cold-agglutinin antibody titers)
Tx:
- macrolide antibiotic (azithromycin)
- doxycycline
- broad-spectrum fluoroquinolone (e.g., levofloxacin, moxifloxacin).
How do you recognize chlamydial pneumonia?
In which patients is it most common?
How is it diagnosed and treated?
cause of atypical pneumonia in adolescents and adults
presents similarly as mycoplasma pneumonia (a long prodrome with gradual worsening of malaise, headaches, dry, nonproductive cough, and sore throat; the fever tends to be low-grade)
dx:
- CXR: patchy, diffuse bronchopneumonia and classically looks impressive, although the patient often does not feel that bad
- negative cold-agglutinin antibody titers, which may cause hemolysis or anemia (compared to mycoplasma pneumonia, which has positive cold-agglutinin antibody titers)
Tx:
- erythromycin in children < 8 years of age
- azithromycin or doxycycline in children > 8 years of age, adolescents, and adults.
In which 2 patient populations do you see Pneumocystis jiroveci pneumonia (PCP) and cytomegalovirus (CMV) pneumonia?
How should you diagnose and treat them?
- HIV-positive patients with CD4 counts < 200/mm3 (AIDS)
- CXR: bilateral interstitial lung infiltrates
- may require bronchoalveolar lavage with silver stain for diagnosis
- trmt: TMP-SMX + corticosteroids
- severely immu- nosuppressed patients (organ transplant recipients on immunosuppressants, patients on cancer chemotherapy)
- intracellular inclusion bodies
- trmt: valganciclovir
What is the best time to treat PCP?
Before it happens.
PCP is acquired when the CD4 count is < 200/mm3. At that point, initiate PCP prophylaxis in an HIV-positive patient with TMP-SMX. Alternatives include dapsone or atovaquone.
specify the organism in this scenario: Stuck with thorn or gardening
Bonus: How should you treat this?
Sporothrix schenckii
Treat with itraconazole
specify the organism in this scenario: Aplastic crisis in sickle cell disease
Parvovirus B19
specify the organism in this scenario: Sepsis after splenectomy 3
Streptococcus pneumoniae
Haemophilus influenzae
Neisseria meningitis
(all encapsulated bacteria)
specify the organism in this scenario: Pneumonia in the Southwest (California, Arizona)
Bonus: How should you treat this?
Coccidioides immitis
Treat with itraconazole or fluconazole; amphotericin B for severe disease
specify the organism in this scenario: Fungus ball/hemoptysis after tuberculosis or cavitary lung disease
Bonus: How should you treat this?
Aspergillus sp.
Describe the three stages of syphilis.
Primary stage: painless chancre that resolves on its own within 8 weeks
Secondary stage: condyloma lata, maculopapular rash (palms and soles of feet), lymphadenopathy; 6 weeks - 18 months later
Tertiary stage: gummas (granulomas in many organs), neurologic symptoms and signs (neurosyphilis, Argyll-Robertson pupil, dementia, paresis, tabes dorsalis, Charcot joints), thoracic aortic aneurysms.; occurs years after initial infection after a latent phase
How do you recognize measles (rubeola) infection in a child?
How are these patients treated?
Look for a lack of immunization, pathognomonic Koplik spots (tiny white spots on buccal mucosa) are seen 3 days after high fever, cough, runny nose, and conjunctivitis +/- photophobia. On the next day, a maculopapular rash begins on the head and neck and spreads downward to cover the trunk (cephalocaudal progression).
Treat supportively.
In which patient population is rubella infection (German measles) an important disease?
in pregnant mothers because an infection can cause severe birth defects in the fetus.
Screen all women of reproductive age and immunize those without evidence of rubella antibodies before pregnancy to avoid this complication.
However, the vaccine is contraindicated in pregnant women.
How do you recognize a rubella infection in children?
What are the complications?
Rubella is milder than measles.
Signs and symptoms: low-grade fever, malaise, and tender swelling of the suboccipital and postauricular lymph nodes; forchheimer spots on soft palate, arthralgias are common. After a 2- to 3-day prodrome, a faint maculopapular rash appears on the face and neck and spreads to the trunk (cephalocaudal progression, just as in measles)
Complications: encephalitis and otitis media, and either acute or late (subacute sclerosing panencephalitis, which usually occurs years later).
How do you recognize roseola infantum (exanthem subitum)?
What causes it?
How common is it?
sx: high temperature (may be ≥ 40°C, 104˚F) with no apparent cause for 4 days, which may result in febrile seizures, followed by an abrupt return to normal temperature just as a diffuse macular/maculopapular rash appears on the chest/abdomen.
Cause: human herpesvirus type 6
Rare in children > 3 yo
How do you recognize erythema infectiosum (fifth disease) in children?
What causes it?
“slapped-cheek” rash accompanied by mild constitutional symptoms (low-grade fever, malaise). One day later, a maculopapular rash appears on the arms, legs, and trunk.
Cause: parvovirus B19, the same virus that causes aplastic crisis in sickle cell disease.
How do you recognize and treat the rash of impetigo?
What causes it?
How is it treated?
caused by Streptococcus and Staphylococcus species
look for
- a history of a break in the skin (previous chickenpox, insect bite, scabies, cut), usually on the face
- localized rash that starts as thin-walled vesicles that rupture and form yellowish crusts; skin is classically described as “weeping.”
- The rash is infectious
Trmt: dicloxacillin, cephalexin, or clindamycin to cover both Streptococcus and Staphylococcus species. Topical mupirocin also may be used.
How do you recognize croup (acute laryngotracheitis)?
Describe the cause and treatment.
parainfluenza virus (75% of cases); influenza virus
Look for
- a child 1 to 2 years of age.
- usually occurs in the fall or winter
- begins with symptoms of viral URI (rhinorrhea, cough, fever);1 to 2 days later patients develop a “barking” cough, hoarseness, and inspiratory stridor
- “steeple sign” (subglottic narrowing of the trachea) on chest/neck xray
Treat with dexamethasone, racemic epinephrine, a mist tent, and humidified oxygen.
How do you recognize epiglottitis?
Describe the cause and treatment.
What should you avoid doing in these children and what is the rationale behind it?
H. influenzae type b (most common), S. aureus, S. pyogenes, and S. pneumoniae
Look for:
- children 2 to 5 years old that were not vaccinated against H. influenza
- little or no prodrome with rapid progression to high temperature, toxic appearance, drooling, and respiratory distress with no coughing.
- The thumb sign (swollen, enlarged epiglottis) on lateral neck xray
Treatment
- Do not examine the throat or irritate the child in any way. You may precipitate airway obstruction.
- be prepared to establish an airway (intubation and, if needed, tracheostomy).
- treat with oxacillin or cefazolin or clindamycin or vancomycin plus cefotaxime or ceftriaxone.
How does streptococcal pharyngitis present?
How do you diagnose and treat it?
Look for
- sore throat
- fever
- tonsillar exudate
- enlarged tender cervical nodes
- leukocytosis
Dx:
- (+) streptococcal throat culture
- Elevated titers of antistreptolysin O (ASO) and anti-DNase antibody for a retrospective diagnosis in patients with rheumatic fever or poststreptococcal glomerulonephritis.
Trmt: penicillin, amoxicillin, cephalosporin, macrolide, or clindamycin to avoid rheumatic fever and scarlet fever.
What are the major and minor Jones criteria for rheumatic fever?
What is required to make the diagnosis?
Why is rheumatic fever less common today?
What should you give all patients affected by rheumatic fever endocarditis?
major: migratory polyarthritis, carditis, subcutaneous nodules, erythema marginatum, and chorea
minor: elevations in ESR, CRP, WBC, and ASO titer; prolonged PR interval on ECG; and arthralgia.
The diagnosis of rheumatic fever requires:
- a history of streptococcal infection AND
- the presence of two major criteria OR one major + two minor criteria.
Treatment of streptococcal pharyngitis with antibiotics markedly reduces the incidence of rheumatic fever; thus it is less common today.
Give all patients affected by rheumatic fever endocarditis antibiotic prophylaxis before surgical procedures, especially dental procedures
Distinguish between impetigo and erysipelas - how are they the same? different?
How should they be treated?
Superficial skin infections caused by Strep or S. aureus and often occur after a break in the skin (e.g., trauma, scabies, insect bite).
Impetigo
- classically changes first from maculopapules to vesicopustules and bullae and then to honey-colored, crusted lesions.
- contagious!
- Staphylococci are a more frequent cause than streptococci
- think of staphylococci if a furuncle or carbuncle is present
- think of streptococci if glomerulonephritis develops
- trmt: dicloxacillin, cephalexin, or clindamycin
Erysipelas
- superficial cellulitis that appears red, shiny, and swollen
- tender
- be associated with vesicles and bullae, fever, and lymphadenopathy
- trmt: penicillin or amoxicillin, may require parenteral therapy with cephalosporin (ceftriaxone or cefazolin) if systemic symptoms such as fever and chills are present
Describe the physical findings of cellulitis.
How does it differ than that of erysipelas?
How do you treat cellulitis?
Both manifest as areas of skin erythema, edema, warmth, and tenderness, BUT
- Erysipelas involves the upper dermis and superficial lymphatics
- Cellulitis involves the deeper dermis and subcutaneous fat.
- Antibiotic selection depends on whether the cellulitis is purulent or nonpurulent.
- purulent (think s. aureus) -> give TMP-SMX, doxycycline, clindamycin, linezolid
- non-purulent -> give dicloxacillin, cephalexin, and clindamycin
- Antibiotic selection depends on whether the cellulitis is purulent or nonpurulent.
