USMLE 2 Infectious Diseases Quick Notes

Cryptococcal meningoencephalitis

Featuresdevelops over 2 weeks (subacute)…
headache, fever, malaise, vomiting,
altered mental status, B/L papilledema
more acute & severe in HIV (CD4 ˂100)
DxCSF features…
➢ high opening pressure
▪ low glucose, high protein
▪ WBC ˂ 50/μL
(mononuclear predominance)
▪ cryptococcal antigen positive
▪ transparent capsule on India ink
▪ culture on Sabouraud agar
Rxinitial: amphotericin B with flucytosine
maintenance: fluconazole
▪ serial LPs may be required to reduce ◇ ICP
▪ antiretroviral therapy should be deferred at least 2 weeks after completing induction
antifungal therapy for cryptococcal meningitis
o initiating retroviral therapy with acute infection
◇ risk of immune reconstitution syndrome
▪ itraconazole does not cross the BBB
➢ best method of reducing maternal-fetal transmission of HIV infection: triple HAART therapy for
the mother throughout pregnancy
▪ HAART: dual NRTI + NNRTI or protease inhibitor
▪ test viral load monthly until undetectable, then every 3 months; CD4 cell count every 3
➢ avoid amniocentesis until viral load undetectable
▪ mothers with undetectable viral loads at delivery have ˂ 1% risk for transmission
▪ intrapartum mother not on HAART: Zidovudine
▪ intrapartum viral load > 1000 copies/mL:
Zidovudine + C-section
▪ infants: Zidovudine for ≥ 6 wks & serial HIV
PCR testing
▪ > 2 weeks of persistent, high-volume, non-bloody watery diarrhea after recent travel; no fever, tenesmus or vomiting: Cryptosporidium parvum
➢ travel-associated diarrhea > 2 weeks; parasitic
o cryptosporidium cystoisospora, microsporidia, Giardia
▪ diarrhea < 1 week: viral or bacterial
o rotavirus/norovirus: vomiting
o ETEC/EPEC: contaminated food/water
o Campylobacter: abdo pain, bloody diarrhea, “pseudoappendicitis”
o Salmonella: frequent fever
o Shigella: fever, bloody diarrhea, abd pain
▪ Entamoeba histolytica causes amebiasis, resulting in abdo pain & bloody diarrhea
▪ primary features of Chagas disease:
recent immigrant from Latin America with chronic
megacolon/megaesophagus & cardiac disease (CHF: pedal edema, JVD, S3, cardiomegaly)
▪ systolic & diastolic heart failure, RBBB
▪ Rx: benznidazole or nifurtimox
▪ painless vesiculopustular rash, tenosynovitis, & migratory polyarthralgia: disseminated
gonococcal infection

▪ 2 – 10 skin lesions similar to furuncles or pimples
▪ Hx of recent unprotected sex with a new partner
➢ all patients should undergo HIV screening
➢ early Lyme disease: erythema chronicum migrans
▪ also a/w headache, malaise, fatigue, fever
▪ unilateral Bell’s palsy
▪ early Dx is based on trademark rash & recent travel
▪ MCC: B. burgdorferi (spirochete)
Rx: oral doxycycline (age > 8)
Rx: oral amoxicillin (age < 8, pregos, or lactating) or cefuroxime

▪ doxycycline A/E: permanent tooth discoloration
& skeletal retardation in children & fetuses
▪ Eikenella corrodens: G-negative anaerobe part of normal oral flora
o infective endocarditis due to E. corrodens is
seen in poor dentition, periodontal infection, or manipulative dental procedures
o E. corrodens belongs to the HACEK group
▪ congenital heart lesions (bicuspid aortic valve, PDA, ToF, VSD) predisposes to risk of IE
▪ ulcerative colon lesions due to colonic neoplasia
or inflammatory bowel disease predisposes to IE due to Strep gallolyticus (S. bovis type I)
▪ S. aureus is the MCC of IE among IVDA
➢ Enterococci (E. faecalis) MC endocarditis a/w nosocomial UTIs
➢ bone marrow transplant recipient with lung & interstitial involvement: CMV pneumonitis
▪ develops 2 wks – 4 months post-transplant
▪ CXR: multi-focal, diffuse patchy infiltrates
▪ high-resolution CT: parenchymal opacification or multiple small nodules
▪ Dx: bronchoalveolar lavage
▪ firm, flesh-colored, umbilicated, dome-shape plaques on trunk, limbs, anogenital areas; spares palms/soles: molluscum contagiosum (poxvirus)
▪ MCC due to sexual contact MC occur on genitalia, lower abdomen, inner thighs
▪ transmitted: skin-skin or fomites
▪ self-limited, localized infection
▪ linear pattern due to spread 2/2 scratching
▪ MC a/w cellular immunodeficiency (HIV), corticosteroid use, chemotherapy
▪ DDx: HSV-1 (vesicular eruption), HPV
(verrucous papules), Staph (furuncles, carbuncles)
▪ Pinworm infection: erythematous vulvovaginitis in prepubertal females; absence of vaginal
▪ recurrent episodes of nocturnal itching should be
examined with “Scotch tape” test
▪ empiric Rx: mebendazole
▪ fever, headache, N/V, petechial rash, stiffness, & photophobia: meningococcemia
▪ fever, arthralgia, sore throat, lymphadenopathy,
mucocutaneous lesions, diarrhea, weight loss:
acute HIV infection
▪ migratory arthritis of large joints, carditis, erythema marginatum (raised ring-shaped
lesions over trunk & extremities), subcutaneous nodules,
Sydenham chorea: acute rheumatic fever
o pharyngitis precedes onset by 2 – 4 wks
▪ sulfadiazine–pyrimethamine:
Rx cerebral toxo (headache, focal neurologic deficits, seizures);
multiple ring-enhancing lesions with edema
▪ CMV retinitis: MC when CD4 < 50
o yellow/white patches of retinal opacification & hemorrhages
o Rx: ganciclovir or foscarnet
▪ HSV encephalitis: cognitive & personality changes, focal neurologic deficits; temporal lobe hemorrhage
▪ PML: JC virus detected on PCR of CSF, patchy areas of white matter due to demyelination
o focal neurologic deficits; no mass effect
o hemiparesis; speech, vision, & gait dysFx
o no cure; 6 month survival
▪ mononucleosis-like symptoms, atypical lymphocytes, negative Monospot: CMV mono
▪ absence of pharyngitis & lymphadenopathy
▪ large basophilic lymphocytes with a vacuolated appearance
▪ +HIV, bloody diarrhea, normal stool: CMV colitis
▪ typically CD4 < 50 cells/μL
▪ Dx: colonoscopy multiple ulcers, mucosal erosions
▪ biopsy: large cells with eosinophilic intranuclear & basophilic intracytoplasmic inclusions
▪ Rx: ganciclovir (or Foscarnet)
▪ complications: toxic megacolon

Duke Criteria for Infective Endocarditis

Major CriteriaMinor Criteria
2 positive blood culture for typical IE organisms (strep viridans or bovis,
S. aureus, enterococcus
Vascular phenomena:
systemic arterial emboli, pulmonary infarcts, mycotic aneurysms, Janeway lesions, conju
Echocardiogram with oscillating intracardiac mass on valveImmunologic phenomena:
rheumatoid factor,
Osler nodes, Roth spots
Dx : 2 Major, 0 Minor
Dx : 1 Major, 3 Minor
Dx : 0 Major, 5 Minor
predisposing heart condition

fever: > 38.0° C (100.4°)

▪ Staph aureus is MCC of healthcare-associated infective endocarditis (S. epidermidis)
o prosthetic valves, indwelling catheters, IVDA, implanted devices (pacemakers, defibrillators)
▪ Streptococci is MCC of community-acquired IE
o viridans strep: S. sanguinis, S. mutans
o after dental procedures or procedures involving incision/biopsy of respiratory tract
▪ Enterococci: E. faecalis: a/w nosocomial UTIs
▪ Strep bovis: S. gallolyticus
o colon cancer & inflammatory bowel disease risk factors
▪ Janeway lesions: macular, erythematous, nontender lesions of palms/soles
▪ Osler’s nodes: painful, violaceous nodules on fingertips/toes
▪ Roth spots: edematous, hemorrhagic retinal lesions
▪ blood cultures from 2 separate venipuncture sites for suspected IE prior to initiating ABX

Endocarditis overview

poor dentition,
congenital heart
disease, valve
intravascular catheters
featuressubungal hemorrhages, petechiae,Janeway
lesions, Osler’s
nodes, Roth spots,
mitral valve disease
labspositive blood cultures,
 WBCs,
septic emboli
Rxvancomycin (initially),
based on cultures

Acute rheumatic fever

epidemiologyMC in females, age 5 – 15 yrs
MCC: group A Strep pharyngitis
precedes onset of ARF by 2 – 4 wks
o Joints (migratory arthritis)
o ♥ (carditis, mitral stenosis)
o Nodules (subcutaneous)
o Erythema marginatum
o Sydenham chorea
fever, arthralgias, elevated ESR/CRP
prolonged PR interval
late featuresmitral regurgitation/stenosis
preventionPCN (regardless of +/- pharyngitis)
➢ Dx: 2 major, or 1 major + 2 minor criteria
▪ supportive findings: ASO titer, Strep antigen test
▪ DDx: SLE, Henoch-Schonlein, Juvenile arthritis
▪ Hx of rheumatic fever increases risk of recurrence & progression of rheumatic heart disease
▪ Dx: continuous ABX prophylaxis to prevent recurrent group A Strep pharyngitis

ABX prophylaxis for rheumatic fever (RF)

➢ IM benzathine PCN G every 4 wks

RF without carditis5 yrs or until age 21
RF with carditis, but no
heart or valvular disease
10 yrs or until age 21
RF with carditis &
persistent ♥ or valve dz
10 yrs or until age 40

Neonatal conjunctivitis etiologies

Chemical˂ 24 hrsmild conjunctival
& tearing after
silver nitrate
eye lubricant
Gonococcal2 – 5 dayseyelid swelling,
purulent exudate,
corneal ulceration
IV or IM
ceftriaxone or
Chlamydia5 – 14 dayseyelid swelling;
chemosis; watery
or mucopurulent
oral erythromycin
➢ best way to prevent neonatal chlamydial & gonococcal conjunctivitis: screen, Dx, Rx pregos
▪ screen for chlamydia @ 1st & 3rd prenatal visit
▪ maternal infection may be asymptomatic
▪ ceftriaxone should be avoided in infants with hyperbilirubinemia ◇ displacement of bilirubin
from albumin-binding sites, ◇ risk of kernicterus
▪ oral erythromycin: Rx chlamydial conjunctivitis
& pneumonia
o risk of infantile hypertrophic pyloric stenosis
➢ topical erythromycin: prophylaxis for neonatal gonococcal conjunctivitis; regardless of
▪ topical silver nitrate: prophylaxis against
penicillinase-producing strains of N. gonorrhea (not available in the US)
▪ nasolacrimal duct obstruction (dacryostenosis):
unilateral chronic tearing & minimal conjunctival injection; Rx massage nasolacrimal ducts
▪ neonatal gonococcal conjunctivitis: acquired through infected genital secretions
▪ prophylaxis: erythromycin ophthalmic ointment
▪ Rx: IV or IM ceftriaxone or cefotaxime
▪ complications: corneal ulcers, scarring, blindness