Infectious Disease confusion pairs
19 Infectious Disease topics students commonly mix up on Step 2 CK, each with the fastest separator, a side-by-side comparison, and a free practice question.
Step 2 CK pairs are in open beta while clinical review finishes. Spot an issue? Tell us.
- UTI uncomplicated vs UTI complicatedAny host or urinary tract complicating factor present at first assessment redirects treatment to the complicated UTI pathway.
- HIV acute vs HIV chronicHigh HIV RNA with negative or indeterminate antibody differentiation after recent exposure is the key discriminator for acute HIV.
- TB primary vs TB reactivationApical cavitary lesion on chest imaging is the quickest discriminator favoring reactivation TB.
- PCP pneumonia vs Bacterial pneumonia in HIVDiffuse bilateral interstitial or ground-glass infiltrates with severe hypoxemia indicate PCP rather than focal bacterial pneumonia.
- Cellulitis vs ErysipelasA sharply demarcated raised border indicates erysipelas rather than diffuse cellulitis.
- Sepsis vs Septic shockNeed for vasopressors after fluid resuscitation is the branch point to septic shock.
- Cellulitis vs Necrotizing fasciitisPain out of proportion with rapid progression is the bedside discriminator for necrotizing fasciitis.
- Campylobacter vs ShigellaRecent undercooked poultry exposure is the quickest clinical clue favoring Campylobacter.
- Sepsis vs SIRSInfection-associated organ dysfunction, such as SOFA increase of at least 2 points, is the key discriminator for sepsis.
- Mononucleosis vs Streptococcal pharyngitisPosterior cervical lymphadenopathy with atypical lymphocytosis points to mononucleosis.
- Lyme disease vs Rocky Mountain spotted feverRash involving palms and soles that started at wrists and ankles is the fastest clue for Rocky Mountain spotted fever.
- Syphilis primary vs Syphilis secondaryDiffuse rash involving palms and soles identifies secondary syphilis rather than primary chancre stage.
- Bacterial endocarditis acute vs Bacterial endocarditis subacuteFulminant febrile illness with rapid valve destruction over days is the immediate discriminator for acute endocarditis.
- Native valve endocarditis vs Prosthetic valve endocarditisPresence of prosthetic valve material is the immediate branch point that changes empiric regimen to include prosthetic-valve coverage.
- Syphilis treatment vs Syphilis Jarisch-Herxheimer reactionFlu-like symptoms starting within 24 hours after first penicillin dose identify Jarisch-Herxheimer reaction.
- Lyme disease early vs Lyme disease lateObjective disseminated organ involvement such as high-grade AV block or meningitis defines late Lyme management.
- Salmonella typhi vs Nontyphoidal SalmonellaPositive blood culture with persistent systemic febrile illness distinguishes typhoid from uncomplicated nontyphoidal gastroenteritis.
- Animal bite cat vs Animal bite dogPuncture morphology from cat teeth is the key discriminator that upgrades infection risk and urgency of prophylaxis.
- Influenza A vs Influenza BPandemic-capable host reassortment is unique to influenza A, while immediate clinical treatment decisions for A and B are otherwise the…