Infectious Disease confusion pairs
35 Infectious Disease topics students commonly mix up on Step 1, each with the fastest separator, a side-by-side comparison, and a free practice question.
- Primary and latent tuberculosis vs Secondary/reactivation tuberculosisPrimary TB is initial Ghon/hilar disease; latent TB is positive test without symptoms; secondary TB is apical cavitary contagious…Video
- Tuberculosis vs SarcoidosisTB is infectious caseating AFB disease; sarcoidosis is noncaseating multisystem granulomatous disease after excluding infection.Video
- Infective endocarditis patterns vs Sterile endocarditis patternsFever/positive cultures point to infective endocarditis; cancer/SLE with sterile culture-negative vegetations points to marantic or…
- Necrotizing fasciitis vs CellulitisNec fasc is toxic, fast, deep, and surgical; cellulitis is superficial soft-tissue infection treated medically unless abscess/complication…Video
- Cellulitis vs ErysipelasCellulitis is deeper and ill-defined; erysipelas is superficial, raised, bright red, and sharply demarcated.Video
- Septic arthritis vs Reactive arthritisSeptic arthritis is hot infected monoarthritis needing drainage; reactive arthritis is sterile post-infectious arthritis with eye/GU/GI…
- Osteomyelitis vs Septic arthritisOsteomyelitis is infected bone/marrow; septic arthritis is infected joint fluid with painful passive motion.
- Diabetic foot infection vs CellulitisDiabetic foot infection is ulcer-based and may be deep/polymicrobial/bone-threatening; cellulitis is skin/subcutaneous infection without…
- Cystitis vs PyelonephritisCystitis is bladder-only dysuria/frequency; pyelonephritis is kidney infection with fever, flank pain, CVA tenderness, or WBC casts.Video
- Early localized Lyme disease vs Early disseminated and late Lyme diseaseEarly localized is single erythema migrans; early disseminated is neuro/carditis/multiple rashes; late Lyme is large-joint arthritis.
- Rocky Mountain spotted fever vs Ehrlichiosis and anaplasmosisRMSF is endothelial vasculitis with classic rash; ehrlichia/anaplasma are cytopenic tick illnesses with morulae and rash less common.
- Typhus vs Typhoid feverTyphus is arthropod-borne rickettsial vasculitis; typhoid is fecal-oral Salmonella Typhi systemic enteric fever.
- Brucellosis vs Tularemia and plagueBrucellosis is undulant dairy/livestock fever; tularemia is rabbit/tick ulceroglandular fever; plague is flea/rodent painful bubo or…
- Leptospirosis vs Lyme disease and syphilisLepto is animal-urine/freshwater fever with calf pain/conjunctival suffusion/kidney-liver injury; Lyme is Ixodes EM/neuro-cardio-joint;…
- Early syphilis vs Latent, tertiary, and congenital syphilisPrimary = chancre; secondary = systemic rash/mucous lesions; latent = serology only; tertiary = gummas/aorta/neuro; congenital =…
- Acute and chronic HIV infection vs AIDSAcute HIV is early viremic mono-like illness; chronic HIV is infection before AIDS criteria; AIDS is CD4 <200 or AIDS-defining illness.
- HIV opportunistic infections at CD4 200-100 vs HIV opportunistic infections below CD4 100 or 50CD4 <200 = PCP; near <100 = toxoplasmosis, cryptococcus, esophageal candidiasis; <50 = MAC and CMV retinitis.
- Pneumocystis pneumonia vs CMV pneumonitis and pulmonary TB in HIVPCP is dry hypoxemic diffuse interstitial pneumonia at CD4 <200; CMV is very-low-CD4 viral pneumonitis; TB is chronic AFB cavitary or…
- CNS toxoplasmosis in HIV vs Primary CNS lymphoma in HIVToxo is usually multiple basal ganglia ring lesions with positive IgG and treatment response; CNS lymphoma is often…Video
- EBV and CMV mononucleosis vs Acute HIV infectionEBV = heterophile-positive pharyngitis/posterior nodes/splenomegaly; CMV = heterophile-negative mono; acute HIV = high RNA/p24 with…
- HSV-1 infection vs HSV-2 infectionHSV-1 is classically oral/trigeminal/encephalitis; HSV-2 is classically genital/sacral/neonatal, with site overlap possible.
- Varicella vs Herpes zosterVaricella is primary diffuse multi-stage rash; zoster is reactivation with painful unilateral dermatomal vesicles.
- Measles and rubella vs Roseola, erythema infectiosum, and hand-foot-mouth diseaseMeasles = 3 C plus Koplik; rubella = mild rash plus posterior nodes/congenital risk; roseola = fever then rash; fifth = slapped cheek;…
- Influenza vs ParainfluenzaInfluenza is abrupt systemic myalgia fever-cough illness; parainfluenza is croup with barking cough and stridor.
- RSV vs Influenza and adenovirusRSV = infant bronchiolitis/wheeze; influenza = abrupt systemic myalgias; adenovirus = pharyngoconjunctival fever or hemorrhagic cystitis.
- Hepatitis A and E vs Hepatitis B, C, and DA/E are fecal-oral acute; B/C/D are bloodborne or sexual/perinatal with chronic/HCC risk; D needs B.
- Rabies vs TetanusRabies is bite/bat encephalitis with hydrophobia; tetanus is contaminated wound toxin causing lockjaw and spasms.
- Severe falciparum malaria vs Relapsing or chronic non-falciparum malariaFalciparum is severe high-parasitemia/cerebral malaria; vivax/ovale relapse from hypnozoites; malariae is chronic quartan/nephrotic risk.
- Amebic dysentery vs Bacillary dysenteryAmebic = E. histolytica trophozoites with ingested RBCs and liver abscess risk; bacillary = acute bacterial inflammatory diarrhea with…
- Giardiasis vs CryptosporidiosisGiardia = greasy foul malabsorption after camping/daycare water; Crypto = watery chlorine-resistant diarrhea, severe in AIDS.
- Schistosomiasis vs Other helminth infectionsSchisto is freshwater skin penetration with venous eggs causing portal/bladder disease; other helminths are keyed by autoinfection,…
- Candidiasis vs Tinea dermatophytes and pityriasis versicolorCandida = mucosal/moist yeast with pseudohyphae; dermatophyte = keratin ringworm hyphae; pityriasis versicolor = Malassezia pigment…
- Histoplasmosis and blastomycosis vs CoccidioidomycosisHisto = macrophage intracellular Ohio/bird-bat; Blasto = broad-based Great Lakes skin/bone; Cocci = Southwest spherules with endospores.
- Aspergillus vs MucormycosisAspergillus = septate acute-angle hyphae; Mucor = broad pauciseptate right-angle hyphae with DKA/black eschar.
- Alveolar opportunistic pneumonia pattern vs Angioinvasive mold pneumonia patternAlveolar PCP pattern is diffuse dry hypoxemic ground-glass disease; angioinvasive Aspergillus pattern is nodular/cavitary with halo,…