USMLE 2 Infectious Diseases Quick Notes
Cryptococcal meningoencephalitis
| Features | develops over 2 weeks (subacute)… headache, fever, malaise, vomiting, altered mental status, B/L papilledema more acute & severe in HIV (CD4 ˂100) |
| Dx | CSF 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 |
| Rx | initial: 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 months ➢ 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 discharge ▪ 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 Criteria | Minor Criteria |
| 2 positive blood culture for typical IE organisms (strep viridans or bovis, S. aureus, enterococcus HACEK) | Vascular phenomena: systemic arterial emboli, pulmonary infarcts, mycotic aneurysms, Janeway lesions, conju hemorrhages |
| Echocardiogram with oscillating intracardiac mass on valve | Immunologic phenomena: glomerulonephritis rheumatoid factor, Osler nodes, Roth spots |
| Dx : 2 Major, 0 Minor Dx : 1 Major, 3 Minor Dx : 0 Major, 5 Minor | predisposing heart condition or IVDA 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
| risk factors | poor dentition, congenital heart disease, valve abnormalities (MVP, MR), IVDA, intravascular catheters |
| features | subungal hemorrhages, petechiae,Janeway lesions, Osler’s nodes, Roth spots, splenomegaly, mitral valve disease (MVP, MR) |
| labs | positive blood cultures, WBCs, glomerulonephritis, septic emboli |
| Rx | vancomycin (initially), based on cultures |
Acute rheumatic fever
| epidemiology | MC in females, age 5 – 15 yrs MCC: group A Strep pharyngitis precedes onset of ARF by 2 – 4 wks |
| Major criteria (“J♥NES”) | o Joints (migratory arthritis) o ♥ (carditis, mitral stenosis) o Nodules (subcutaneous) o Erythema marginatum o Sydenham chorea |
| Minor criteria | fever, arthralgias, elevated ESR/CRP prolonged PR interval |
| late features | mitral regurgitation/stenosis |
| prevention | PCN (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 carditis | 5 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
| Onset | Features | Rx | |
| Chemical | ˂ 24 hrs | mild conjunctival irritation/ injection & tearing after silver nitrate ophthalmic prophylaxis | eye lubricant |
| Gonococcal | 2 – 5 days | eyelid swelling, purulent exudate, corneal ulceration | IV or IM ceftriaxone or cefotaxime |
| Chlamydia | 5 – 14 days | eyelid swelling; chemosis; watery or mucopurulent discharge | 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 screening ▪ 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 |
