Infectious Diseases
7 high-yield topics. Open a topic to review its pearls.
Meningitis
CSF findings and empiric therapy
CSF Findings
- Bacterial: high pressure, neutrophils, high protein, low glucose (under 40), positive gram stain
- TB: lymphocytes, high protein, low glucose
- Cryptococcal: lymphocytes, India ink positive
- Viral/aseptic: lymphocytes, normal glucose
Empiric Therapy by Age
- Age 2-50: vancomycin + 3rd gen cephalosporin
- Age over 50 or immunocompromised: add ampicillin (Listeria)
- Dexamethasone before antibiotics
- If LP delayed for CT, start empiric antibiotics
Special Situations
- Meningococcal exposure: rifampin prophylaxis for close contacts
- HSV encephalitis: RBCs in CSF, olfactory hallucinations, IV acyclovir
- West Nile: mosquito exposure, polio-like weakness
Endocarditis
Duke criteria and treatment
Diagnosis
- Major triad: fever, murmur, positive blood cultures
- Duke criteria: 2 major, or 1 major + 3 minor, or 5 minor
- Blood cultures before antibiotics, then TTE/TEE
Organisms
- Native acute: Staph aureus
- Native subacute: Strep viridans, Strep bovis (do colonoscopy for malignancy)
- Prosthetic: Staph epidermidis, vanco + genta + rifampin
- IVDU: Staph aureus (tricuspid), gram negatives, fungi
Surgery Indications
- CHF from valve dysfunction
- Persistent positive cultures over 6 days
- Fungal infection
- Paravalvular abscess (heart block on EKG)
HIV/AIDS
Diagnosis, HAART, opportunistic infections
Diagnosis
- ELISA screen, confirm with Western blot
- Antibodies detectable 3 weeks to 3 months (window up to 6 months)
- Viral load for monitoring
CD4-Based Prophylaxis
- Under 200: PCP prophylaxis (TMP/SMX)
- Under 100: toxoplasmosis prophylaxis
- Under 50: MAC prophylaxis (azithromycin)
- Start HAART at diagnosis regardless of CD4
HAART Side Effects
- NRTIs: lactic acidosis, steatosis; abacavir hypersensitivity; tenofovir renal
- NNRTIs: rash; efavirenz vivid dreams (contraindicated in pregnancy)
- PIs: lipodystrophy, hyperlipidemia; indinavir nephrolithiasis
- Zidovudine: macrocytic anemia
Opportunistic Infections
- PCP: dry cough, elevated LDH, silver stain of BAL; add steroids if A-a over 35 or pO2 under 70
- Toxoplasmosis: multiple ring-enhancing lesions, pyrimethamine + sulfadiazine
- CNS lymphoma: EBV positive, usually solitary
- Cryptococcal meningitis: repeat LP for elevated pressure
STDs and GU Infections
Syphilis, gonorrhea, chlamydia, UTI
Syphilis
- Primary: painless ulcer, darkfield microscopy, benzathine PCN
- Secondary: rash on palms/soles, condyloma lata
- Tertiary: cardiac, ophthalmic, gummas
- Neurosyphilis: Argyll Robertson pupil, IV PCN
Other STDs
- Gonorrhea: purulent discharge, ceftriaxone + treat partner
- Chlamydia: mucopurulent, azithromycin/doxycycline
- HSV: painful ulcers, acyclovir
- Chancroid: painful ulcer (Do Cry), school of fish
UTIs
- Cystitis: 3 days TMP/SMX or fluoroquinolone
- Pyelonephritis: 10-14 days; pregnancy ampicillin
- Asymptomatic bacteriuria: treat only in pregnancy, transplant, neutropenia, pre-urologic procedure
Tick-Borne Diseases
Lyme, RMSF, ehrlichiosis, babesiosis
Lyme Disease
- Borrelia burgdorferi, Ixodes tick
- Early: erythema chronicum migrans
- Disseminated: Bell palsy, aseptic meningitis, heart block, carditis
- Late: monoarticular arthritis
- Treatment: doxycycline/amoxicillin; ceftriaxone for cardiac/neuro
- Prophylaxis: doxycycline 200mg x1 if attached over 2 days
Other Tick Diseases
- RMSF: rash extremities to trunk, doxycycline
- Ehrlichiosis: elevated LFTs, thrombocytopenia, doxycycline
- Babesiosis: Maltese cross, hemolytic anemia, clinda + quinine
Zoonoses
Animal-associated infections
Common Associations
- Cat scratch: Bartonella henselae, doxycycline
- Dog/cat bite: Pasteurella, amox-clavulanate
- Rabbit hunter: Tularemia (Francisella), streptomycin
- Vets/farmers: Q fever (Coxiella), doxycycline
- Sewage workers: Leptospirosis, doxycycline
- Postal worker/hides: Anthrax (Bacillus), cipro/PCN
Antibiotic Associations
Key drug pearls
Antibiotic Pearls
- Vancomycin: red man syndrome, slow infusion
- Linezolid: neutropenia, serotonin syndrome
- Imipenem/fluoroquinolones: lower seizure threshold
- PCN for syphilis: Jarisch-Herxheimer reaction
- Bactrim: aseptic meningitis, increased creatinine
- Ampicillin: Listeria treatment