Infectious Diseases

A 64-year-old man presents with fever 39.2°C, tachycardia 118/min, BP 86/54 mmHg, confusion, and warm extremities. Lactate is 4.8 mmol/L. He received antibiotics 1 hour ago in the ED.

A 71-year-old woman with neck stiffness, photophobia, and fever 38.9°C has suspected bacterial meningitis. She is immunocompetent and has no focal deficits.

A 55-year-old man with severe pain and swelling of the thigh after a small abrasion 24 hours ago; skin is tense with bullae, crepitus, and pain out of proportion.

A 63-year-old man with diabetes has a chronic plantar ulcer. Probe-to-bone is positive; ESR 88 mm/h; X-ray equivocal.

A 72-year-old man develops a hot, swollen prosthetic knee 18 days after arthroplasty; synovial WBC is high with neutrophil predominance; cultures pending.

A 29-year-old IV drug user has fever and pleuritic chest pain. CXR shows multiple cavitary nodules; blood cultures grow MSSA.

A 62-year-old man with Streptococcus gallolyticus (bovis) endocarditis responds to therapy. What additional evaluation is needed?

A 48-year-old woman with a tunneled central line develops fever and rigors; blood cultures from line and periphery grow Candida albicans.

A pregnant 26-year-old (18 weeks) has asymptomatic bacteriuria on screening urine culture (E. coli 10⁵ CFU/mL).

A 32-year-old woman at 24 weeks gestation presents with flank pain, fever, and CVA tenderness; urine has WBCs and bacteria.

A 22-year-old man with dysuria and purulent urethral discharge.

A 28-year-old woman with lower abdominal pain, cervical motion tenderness, and mucopurulent discharge. Pregnancy test negative.

A 25-year-old man has a painless penile ulcer with indurated edges; VDRL positive.

A 54-year-old man with HIV (CD4 420) has decreased vibration sense; RPR high titer; CSF-VDRL positive.

A nurse sustains a needlestick from a patient with unknown HIV status. She presents 2 hours after exposure.

A 33-year-old man with HIV (CD4 120) asks about prophylaxis.

A 28-year-old healthcare worker has a positive IGRA, normal CXR, and no symptoms.

A 45-year-old man with cough, weight loss, and night sweats has CXR with cavitary upper lobe lesion; sputum AFB positive.

A 52-year-old man starting isoniazid for LTBI develops paresthesias in fingers.

A 31-year-old woman returns from South Asia with periodic fevers and anemia. Thick and thin smears show ring forms and high parasitemia.

A 27-year-old traveler to the Amazon develops fever, chills, and splenomegaly; smear shows Plasmodium vivax.

A 30-year-old man returns from Southeast Asia with high fever, severe myalgias, retro-orbital pain, and a positive tourniquet test; platelets 75,000/µL.

A 19-year-old student has fever, pharyngitis, posterior cervical LAD, and splenomegaly; heterophile antibody test positive.

A 42-year-old butcher has fever, hepatosplenomegaly, and undulating fevers; blood culture grows Brucella.

A 34-year-old hiker develops expanding erythematous rash with central clearing on thigh after a tick bite in an endemic area; mild fever and myalgias.

A 49-year-old man with AV block and migratory arthralgias after untreated Lyme disease.

A 72-year-old woman with fever, hyponatremia, nonproductive cough, diarrhea, and relative bradycardia; urine antigen positive for Legionella.

A 67-year-old COPD patient presents with community-acquired pneumonia and multiple comorbidities.

A 64-year-old hospitalized patient on broad antibiotics develops profuse watery diarrhea and abdominal cramping; stool toxin positive.

A 41-year-old man has a cat bite on the hand 8 hours ago; wound is punctate with mild swelling.

A 36-year-old woman with a clenched-fist human bite to the knuckle.

A 58-year-old man with fever, new murmur, and positive blood cultures for Enterococcus faecalis; TEE shows aortic valve vegetation.

A 29-year-old asplenic man (post-splenectomy) presents with fever and rigors; appears ill with hypotension.

A 45-year-old man with severe odynophagia and oral thrush; CD4 90/µL.

A 37-year-old woman has dysuria, sterile pyuria, and suprapubic discomfort after a new sexual partner; NAAT positive for Chlamydia trachomatis.

A 61-year-old diabetic woman has severe pain, swelling, and violaceous discoloration of the perineum with crepitus and foul odor.

A 52-year-old man with new mitral valve prosthesis develops fever 6 weeks post-op; blood cultures grow coagulase-negative staphylococci.

A 44-year-old man with symptomatic COVID-19 requiring low-flow oxygen and elevated inflammatory markers.

A 79-year-old nursing home resident with indwelling catheter has cloudy urine but no symptoms. UA shows pyuria and bacteriuria.

A 33-year-old woman bitten by a stray dog on the calf presents 12 hours later. She is uncertain about prior rabies vaccination. Wound is superficial but breaks skin.

A 58-year-old man with fever and chills has two sets of blood cultures positive for MRSA; no obvious focus. TTE is nondiagnostic.

A 67-year-old man with MRSA bacteremia develops severe back pain and fever; ESR/CRP high. Neuro exam normal.

A 54-year-old woman with MSSA native-valve endocarditis has persistent bacteremia after 72 hours of nafcillin; TEE shows large mobile vegetation with severe MR.

A 62-year-old man 10 days after aortic valve replacement develops fever; blood cultures grow MRSA.

A 65-year-old man with acute swollen, painful knee; fever 38.6°C; synovial WBC 95,000 (90% PMNs).

A 21-year-old woman with migratory polyarthralgia, tenosynovitis, and a few painless pustules on the hands.

A 78-year-old immunocompromised woman with headache, fever, and neck stiffness.

A 41-year-old man with otitis/mastoiditis develops focal neurologic deficits; MRI shows a ring-enhancing frontal lesion.

A 63-year-old diabetic has severe otalgia and granulation tissue in the ear canal; ESR high; cranial neuropathies begin.

A 22-year-old after severe pharyngitis develops fever, neck pain/swelling, and septic pulmonary emboli; blood cultures grow Fusobacterium.

A 12-year-old boy with tender axillary nodes weeks after a kitten scratch; low-grade fever.

A 46-year-old man has well-demarcated, bright-red, raised plaque on the face with fever; lymphangitic streaking present.

A 5-year-old child has honey-colored crusted lesions around the nose and mouth; afebrile.

A 39-year-old fishmonger develops violaceous, tender plaques on the hand after a finger prick; mild fever.

A 58-year-old man with cirrhosis develops fever and hemorrhagic bullae after eating raw oysters.

A 33-year-old river kayaker has rapidly progressive cellulitis after a freshwater laceration.

A 29-year-old with a dirty puncture wound and unknown vaccination status develops trismus.

A 7-year-old with sore throat, low-grade fever, gray pharyngeal pseudomembrane, and cervical LAD; unvaccinated.

A 34-year-old has paroxysmal cough with inspiratory whoop and posttussive emesis for 3 weeks.

A 27-year-old camper presents with fever, myalgias, cough, and rapidly progressive respiratory failure; exposure to rodent droppings.

A 25-year-old triathlete with conjunctival suffusion, jaundice, and myalgias after freshwater swim in tropics.

A hunter develops an ulcer at the finger with tender regional nodes after skinning a rabbit; cultures negative.

A 20-year-old with sudden high fever and painful bubo after flea exposure; chest pain and hemoptysis later.

A 44-year-old mailroom worker has dyspnea, fever, diaphoresis; CXR: widened mediastinum; pleural effusion.

A 59-year-old shepherd with culture-negative endocarditis, night sweats, and exposure to parturient animals.

A 33-year-old from a sheep-farming region has a large hepatic cyst with daughter cysts on ultrasound.

A 6-year-old with pica has fever, cough, hepatomegaly, and eosinophilia; dog exposure.

A 48-year-old on high-dose steroids develops gram-negative sepsis and strongyloides larvae in sputum.

A 22-year-old swimmer in sub-Saharan Africa develops painless hematuria; urine microscopy shows terminal spined ova.

A 35-year-old immigrant with seizures has multiple parenchymal brain cysts with scolex on MRI.

A 29-year-old man with RUQ pain, fever, and tender hepatomegaly; ultrasound shows a solitary liver abscess; stool O&P negative; serology positive for Entamoeba.

A 26-year-old backpacker has foul-smelling, greasy diarrhea and bloating after drinking stream water.

A 30-year-old in a refugee camp has profuse “rice-water” stools and dehydration.

A 4-year-old with dysentery, seizures, and leukocytosis; stool shows Shigella.

A 23-year-old has bloody diarrhea after eating undercooked beef; afebrile; platelets drop; creatinine rises.

A 28-year-old with fever and bloody diarrhea after poultry ingestion; stool culture grows Campylobacter.

A 27-year-old returns from South Asia with step-ladder fevers, rose spots, relative bradycardia, and constipation.

A 34-year-old immunocompetent adult with non-typhoidal Salmonella gastroenteritis, mild dehydration, and fever 38.2°C.

A 23-year-old woman with uncomplicated cystitis (dysuria, frequency, no fever/flank pain); UA positive for nitrites/leukocyte esterase.

A 59-year-old man with fever, perineal pain, dysuria, and a tender boggy prostate on DRE.

A 70-year-old ventilated ICU patient develops fever, purulent secretions, and new infiltrate after 6 days on the ventilator. Prior IV antibiotics in the last week; hospital has high MRSA and Pseudomonas prevalence.

A 76-year-old man with an indwelling Foley has fever and suprapubic pain; UA shows pyuria and bacteriuria; no other source.

A 23-year-old man with acute scrotal pain and dysuria; sexually active with new partner; UA shows pyuria; cremasteric reflex intact; Prehn sign positive.

A 19-year-old stepped on a nail through a rubber-soled shoe; 2 weeks later, painful swollen foot; X-ray shows osteolysis of 5th metatarsal.

A 64-year-old man with persistent S. aureus bacteremia develops LUQ pain and fever; CT shows a multiloculated splenic abscess.

A renal transplant recipient on tacrolimus presents with subacute cough, weight loss, and multiple ring-enhancing brain lesions; sputum weakly acid-fast branching filaments.

A prolonged neutropenic leukemia patient has fever, pleuritic chest pain, and CT with nodules and “halo sign.”

A man with DKA develops necrotic black nasal eschar and cranial neuropathies; CT shows sinus invasion.

A spelunker from the Ohio River Valley has fever, hilar lymphadenopathy, and calcified granulomas; urine antigen positive.

A forestry worker has chronic cough, verrucous skin lesions, and lytic bone lesions; CXR with upper lobe infiltrate.

A pregnant woman in Arizona has fever and diffuse erythema nodosum; CXR shows thin-walled cavities; serology positive for coccidioides.

A 29-year-old with HIV (CD4 60) has dyspnea, dry cough, fever; CXR shows bilateral interstitial infiltrates; LDH high; PaO₂ 64 mmHg.

A 36-year-old with AIDS has painless progressive vision loss and floaters; fundus: fluffy yellow-white lesions with hemorrhage (“pizza pie”).

A kidney transplant recipient has fever, abdominal pain, watery diarrhea, and colitis on colonoscopy with giant cells.

A 42-year-old with CD4 24 presents with fever, night sweats, weight loss, anemia; blood cultures (mycobacterial) grow MAC.

A 28-year-old woman’s HBV serology: HBsAg negative, anti-HBs negative, anti-HBc IgM positive.

A lymphoma patient starting rituximab is HBsAg negative, anti-HBc positive, anti-HBs negative.

A 55-year-old with chronic HCV (no cirrhosis) asks about treatment. Genotype pending; minimal comorbidities.

A 26-year-old pregnant woman (third trimester) has acute hepatitis with very high bilirubin in South Asia.

A household contact of a confirmed HAV case presents 10 days after exposure; he is unvaccinated and immunocompetent.

An unvaccinated healthcare worker exposed to a measles patient 48 hours ago; no evidence of immunity.

A 30-year-old pregnant woman (nonimmune to varicella) exposed at work; 3 days since exposure.

A 54-year-old with forehead vesicular rash respecting the midline, conjunctival injection, and tip-of-nose lesions.

A 36-year-old at 36 weeks gestation with recurrent genital HSV asks about delivery plan.

A 28-year-old woman with green, frothy discharge and vigorous cervical motion tenderness; NAAT positive for Trichomonas.

A 24-year-old woman with thin, gray, fishy-smelling vaginal discharge; positive whiff test; clue cells on microscopy.

A 29-year-old man has persistent urethritis after appropriate GC/CT therapy; NAAT for Mycoplasma genitalium is positive.

A 22-year-old with exudative pharyngitis tests positive for gonorrhea in the pharynx.

A 33-year-old MSM presents with rectal pain, bleeding, and tenesmus; NAAT positive for C. trachomatis L1–L3.

A migrant farmer has anesthetic hypopigmented skin patches and peripheral nerve enlargement with sensory loss.

A 44-year-old woman with poor dentition develops jaw mass with draining sinus producing “sulfur granules.”

A 39-year-old Bolivian immigrant has palpitations; ECG shows RBBB with left anterior fascicular block; serology positive for Trypanosoma cruzi.

A patient starting prolonged high-dose steroids for vasculitis has eosinophilia and lived in Southeast Asia for years.

A pregnant woman at 18 weeks has serology showing acute toxoplasmosis; fetal ultrasound normal.

A 17-year-old has fever, exudative sore throat, tender anterior cervical nodes, and no cough. Rapid antigen for GAS is positive.

A 15-year-old develops migratory polyarthritis, carditis (new MR), chorea, and erythema marginatum 3 weeks after untreated strep throat.

A 7-year-old with fever, sore throat, and sandpaper-like rash with strawberry tongue; rapid strep positive.

A tampon-using woman presents with fever, hypotension, diffuse rash, and multiorgan involvement; blood cultures later grow S. aureus.

A patient on peritoneal dialysis develops abdominal pain, cloudy dialysate, and fever; PD fluid WBC >100/µL with >50% PMNs.

A 52-year-old with repaired congenital heart disease asks about antibiotics before a dental cleaning.