Organism & Syndrome Index

A Cheesy Clue

Mycobacterium bovis

Infectious differential for chronic diarrhea and edema.

A Cryptic Case

Cryptococcus gattii

When CNS cryptococcosis reveals an acquired immune defect.

A Dangerous Predilection

Salmonella enterica

A man with a known aortic aneurysm, a forgotten diarrheal illness, and blood cultures that explain everything.

A Firestorm After the Cure

Mycobacterium leprae

A man from the Peruvian Amazon develops abrupt fever, painful nodular crops, neuritis, and orchitis several months after completing multidrug therapy for multibacillary leprosy.

A Nose Lesion that Wouldn’t Heal

Klebsiella rhinoscleromatis

A chronic nasal lesion with a broad differential diagnosis.

A Quiet Invasion

Entamoeba histolytica

A returning traveler with RUQ pain, fever, and a hypodense hepatic lesion — and no culturable bacteria.

A Shot in the Dark

HIV-1

Choosing the right ART when prevention was an injection.

A Stubborn Course

Cytomegalovirus, CMV

A kidney transplant recipient who completed C. diff treatment but keeps getting worse — the biopsy reveals who was really behind it.

Acute Dysentery in a Returning Aid Worker

Shigella flexneri

A high-yield cause of acute bloody diarrhea.

After the Extraction

Streptococcus mitis, Viridans streptococci

Acute knee pain in a patient with a prosthetic joint after a dental procedure.

After the Headaches Faded

JC polyomavirus

A patient with advanced HIV develops worsening focal deficits and a left frontal white matter lesion with midline shift after ART initiation.

After the Lithotripsy

Pseudomonas aeruginosa

Bacteremic difficult-to-treat Pseudomonas after urinary instrumentation and residual stone burden.

After the Steroid Burst

Strongyloides stercoralis

ICU shock, pulmonary infiltrates, and diarrhea after immunosuppression.

Amazon Adventure

Lacazia loboi

A returning traveler lesion.

At the Tip of the Nose

Varicella-zoster virus

A unilateral facial eruption with ocular risk and a misleading early course.

Before Day Forty-Two

Toxoplasma gondii

A woman with AML develops focal neurological deficits and confusion on day thirteen after allogeneic bone marrow transplantation, before prophylaxis has been started.

Bloody Diarrhea Without a Clear Cause

Brachyspira aalborgi

An unexpected culprit.

Chronic Hemoptysis in a Traveler from Rural Colombia

Paragonimus westermani

When lung flukes mimic TB.

Contaminant

Rhodococcus equi

A gram-positive coccobacillus dismissed as a diphtheroid contaminant in a patient with advanced HIV and a cavitary lung lesion.

Desert Screening Dilemma

Coccidioides immitis

An HIV follow-up case.

Fever after Floodwaters

Leptospira interrogans

A rice farmer presents with fever, jaundice, and renal failure after wading through floodwaters.

Fever after the Coffee Farms

Yellow fever virus

A traveler returning from coffee farms in Tolima, Colombia develops fever, early jaundice, thrombocytopenia, and transaminitis.

Fever and Arthralgia after Caribbean Travel

Chikungunya virus

A traveler returning from the Dominican Republic presents with fever, severe polyarthralgia, and rash. Diagnose and manage this arboviral infection.

Fever and Cytopenias After Heart Transplant

Parvovirus B19

When the Marrow Goes Quiet

Fever During Alemtuzumab Therapy

Cytomegalovirus

An opportunistic infection clue during lymphocyte-depleting therapy.

Fever From the Forest

Orientia tsutsugamushi

Fever, rash, and a painless black-crusted ulcer after trekking in rural Nepal.

Fever in the Ozarks

Ehrlichia chaffeensis

A deer hunter from rural Missouri presents with four days of fever, leukopenia, thrombocytopenia, and transaminitis after removing ticks from his legs.

Fever, Hemolysis, and Bleeding Papules After Andes Travel

Bartonella bacilliformis

A classic biphasic Bartonella bacilliformis syndrome.

Fever, Urinary Symptoms, and a Heart Murmur

Aerococcus urinae

Beyond the obvious: Gram-positive clusters.

Follicles Beneath the Upper Lid

Chlamydia trachomatis

Chronic conjunctivitis in a child from rural Ethiopia.

Forgotten but Not Gone

Haemophilus influenzae, Haemophilus influenzae type b

An unvaccinated adult with bacterial meningitis and a Gram stain that tells the whole story.

Fulminant Shock

Streptococcus suis

Shock in the Slaughterhouse

Headache, Ataxia, and Sixth Nerve Palsy in Connecticut

Powassan virus

Brief attachment

Heart Failure from the Andes

Trypanosoma cruzi

A Colombian immigrant presents with progressive heart failure and characteristic cardiac findings.

Hidden in Plain Sight

Histoplasma capsulatum

A patient with newly diagnosed HIV, a CD4 of 18, and a bone marrow that told the whole story.

Hundreds of Lesions

Tunga penetrans

Neglect, poverty, and a devastating skin disease.

Jaw Stiffness in a Visitor from Rural Haiti

Clostridium tetani

An early neurologic warning sign with a dangerous trajectory.

Legs from the Bush

Rickettsia africae

A safari traveler returns with fever, regional nodes, and multiple eschars on the legs.

Lights Out on Postoperative Day 21

Seizure and cortical blindness in a kidney transplant recipient on tacrolimus.

Memory Lost

HHV-6B, Human herpesvirus 6

A post-BMT patient with progressive amnesia, seizures, and a viral PCR result that demands a second look.

New HIV Diagnosis in a Patient on Hemodialysis

HIV-1

Selecting initial ART in end-stage kidney disease on dialysis.

Not the Cat's Fault

Rickettsia typhi

A South Texas woman with cats, a flea, and a fever that didn't need a tick to get started.

Paresthesias in Paradise

Angiostrongylus cantonensis

Severe headache, migratory paresthesias, and a CSF full of eosinophils after a Hawaiian farm dinner.

Persistent Diarrhea and Flatulence After Travel to India

Giardia lamblia

Greasy stools, bloating after dairy, and a classic travel-related cause of persistent diarrhea.

Persistent Fever, Splinter Hemorrhages, and an Aortic Valve Abscess

Brucella melitensis

A culture-negative endocarditis clue hiding in the exposure history.

Phase I vs Phase II

Coxiella burnetii

Culture-negative endocarditis, seronegative arthralgias, and a serologic pattern that flips the expected phase response.

Positive, But Wrong

Trichosporon asahii

A neutropenic BMT recipient with a positive CrAg and skin lesions that pointed elsewhere.

Postpartum Fever, Diplopia, and Hemiparesis

Listeria monocytogenes

A stroke-mimic presentation of postpartum brainstem infection.

Progressive Spastic Paraparesis in a Woman from Guyana

HTLV-1

A tropical differential for myelopathy.

Quiet Enzymes

Hepatitis E virus

A kidney transplant recipient on tacrolimus presents with asymptomatic transaminase elevation and a dietary exposure that points away from the usual suspects.

Recurrent Pneumococcemia

Streptococcus pneumoniae

Recurrent invasive pneumococcal disease with a subtle hematologic clue.

Resistance by Default

Enterococcus gallinarum

Not all vancomycin resistance is created equal.

Salt and Iron

Vibrio vulnificus

Necrotizing fasciitis with hemorrhagic bullae in a fisherman with hemochromatosis after a minor saltwater laceration — curved gram-negative rods and septic shock within 48 hours.

Severe Hypertension and Renal Failure in Western Mozambique

Schistosoma haematobium

A tropical cause of bilateral obstructive uropathy and renal failure.

Slowly Progressive Lumbar Mass

Actinomyces israelii

When a soft-tissue mass is an indolent infection.

Soft Edges and a Swollen Groin

Haemophilus ducreyi

A painful genital ulcer that resists easy categorization.

Symmetric Groin Plaques in a Man With Diabetes

Corynebacterium minutissimum

An intertriginous rash with a key bedside clue.

The 5-Month Mystery

Staphylococcus epidermidis

A new murmur and persistent fevers follow heart surgery.

The Absent Shield

Mycobacterium avium complex

A previously healthy Vietnamese-born woman presents with four months of fevers, weight loss, and massive lymphadenopathy. HIV is negative and CD4 is normal.

The Bite You Didn't Feel

Oropouche virus

An Amazon traveler returns with a dengue-like illness and a vector most clinicians do not think to ask about.

The Blinding Cycle

Chlamydia trachomatis

A community health worker in rural Ethiopia with bilateral eye irritation and follicles on the upper tarsal conjunctiva — the world's leading infectious cause of blindness.

The Border She Couldn't Cross

Plasmodium falciparum, Plasmodium vivax, Plasmodium ovale

Choosing malaria chemoprophylaxis when the patient is pregnant and the itinerary hits a resistance border.

The Brainstem Under Siege

Enterovirus A71, EV-A71

A rituximab-treated adult in Vietnam with brainstem encephalitis, myoclonus, and a characteristic MRI pattern after contact with hand-foot-and-mouth disease.

The Breast Mass That Wasn’t Cancer

Corynebacterium kroppenstedtii

A suspicious breast mass with a hidden microbiologic cause.

The Case of the Returning Fever

Borrelia recurrentis

Recurrent fever, jaundice, and a diagnosis hiding in the clothing seams.

The Cavity That Came Back

Aspergillus fumigatus

A Peruvian man treated for TB years ago returns with weight loss, hemoptysis, and an old cavity now containing a fungal ball.

The Cellulitis That Kept Coming Back

Brugia malayi, Wolbachia

Recurrent leg swelling, a healing inguinal scar, and a blood draw that had to wait until midnight.

The Climbing Lesion

Nocardia brasiliensis

Not your routine skin and soft tissue infection.

The Color of the Cure

Mycobacterium tuberculosis

A patient on a clofazimine-containing MDR-TB regimen develops progressive purple skin, ichthyosis, and a borderline QTc.

The Copper Penny Sign

Fonsecaea pedrosoi

A Brazilian farmer with a 3-year verrucous plaque and a pathognomonic tissue finding.

The Culture That Changed the Scope

Streptococcus gallolyticus, S. bovis/equinus group

Subacute endocarditis caused by Streptococcus gallolyticus subsp. gallolyticus leading to discovery of colorectal neoplasia — the strongest organism-disease association in clinical infectious diseases.

The Cytokine Storm Within

Human herpesvirus 8, HHV-8, KSHV

Diffuse lymphadenopathy, a hyperinflammatory state, and plasmablasts in an HIV-positive patient with an enhancing retroperitoneal mass.

The Daughter Within

Echinococcus granulosus

A young woman from Patagonia with a large multiloculated liver cyst containing daughter cysts — and a planned biopsy that must not proceed.

The Dust That Wouldn't Settle

Coccidioides immitis

Subacute basilar meningitis in a Filipino-American construction worker from Arizona.

The Eosinophils Knew

Enterobius vermicularis

Eosinophilic appendicitis caused by a nematode with pathognomonic lateral alae, discovered on pathology after appendectomy in a young woman.

The Eye of the Rabbit

Francisella tularensis

A hunter from Arkansas who field-dressed a rabbit without gloves now has a red eye, a golf ball-sized preauricular node, and a corneal ulcer that is not pink eye.

The Fever That Would Not Wait

Mycobacterium tuberculosis, HIV-1

TB meningitis in a newly diagnosed HIV patient — treatment timing and ART selection.

The Fig Tree Fever

Rickettsia typhi

A Los Angeles resident develops nine days of fever, headache, and a subtle truncal rash after exposure to cats and backyard wildlife.

The Fluke in the Bile Duct

Clonorchis sinensis

Painless jaundice, a hilar mass, and bile duct flukes in a Korean immigrant with decades of raw fish consumption.

The Forgotten Toe

Staphylococcus aureus, Streptococcus agalactiae

A diabetic foot ulcer that wouldn't heal, leading to osteomyelitis and amputation.

The Gardener's Finger

Sporothrix schenckii complex

A gardening injury that did not behave like routine cellulitis.

The Great Imitator

Treponema pallidum

A rash that reaches the palms and a genital sore the patient thought had healed.

The Hike and the Tender Node

Yersinia pestis

A camper in California's Sierra Nevada develops fever and a painful inguinal node after a small bite near the ankle.

The Indeterminate Answer

Mycobacterium tuberculosis, HIV-1

A man with newly diagnosed HIV and a CD4 of 118 whose household partner has pulmonary TB — and a QuantiFERON result that demands careful interpretation.

The Joint Pain Before the Murmur

Tropheryma whipplei

Culture-negative endocarditis, chronic arthralgias, and PAS-positive macrophages on valve tissue.

The Long Sleep

Plasmodium vivax

A humanitarian aid worker presents with cyclical fevers six months after returning from Papua New Guinea despite completing her malaria prophylaxis correctly.

The Long Way Home

Trypanosoma brucei gambiense

A humanitarian aid worker returning from the DRC with progressive neuropsychiatric symptoms and a blood smear that tells the whole story.

The Loyal Companion

Capnocytophaga canimorsus

Septic shock and meningitis in an asplenic patient whose dog never bit her.

The Margin That Moved by the Hour

Streptococcus pyogenes, Group A Streptococcus

A healthy gardener develops necrotizing fasciitis with streptococcal toxic shock after a minor abrasion.

The Mass at Twelve Months

Epstein-Barr virus, EBV

A heart transplant recipient with fever, night sweats, and a left upper lobe mass one year after transplant.

The Mulberry Wound

Paracoccidioides brasiliensis

A progressive granular nasal ulcer in a Venezuelan coffee farmer.

The Negative CrAg

Candida tropicalis, Candida

A leukemia patient with cleared candidemia on micafungin develops meningitis with a negative cryptococcal antigen — and a sanctuary-site drug failure.

The Negative Test and the Worsening Lungs

Legionella pneumophila, Legionella species

An immunosuppressed patient develops progressive multilobar pneumonia despite standard therapy and an initially reassuring test result.

The Nerve Below the Surface

Mycobacterium leprae

Progressive foot drop and hand weakness in an immigrant with no skin lesions — and a diagnosis hiding in the nerves.

The New Infiltrates on Week Three

Staphylococcus aureus

A patient receiving outpatient therapy for MRSA bacteremia returns with fever, hypoxemia, and new bilateral pulmonary infiltrates.

The Nodules Before the Headache

Aspergillus fumigatus

A kidney transplant recipient with recent rejection therapy develops cavitary pulmonary nodules and ring-enhancing brain lesions.

The Normal Lung Exam

Pneumocystis jirovecii

A young patient develops progressive breathlessness with little to hear on lung exam.

The Painful Mouth and the Quiet Lungs

Mycoplasma pneumoniae

A young woman with severe oral mucositis, minimal skin disease, and subtle pulmonary findings.

The PCR That Climbed

Cytomegalovirus, CMV

A lung transplant recipient's rising CMV viral load despite ganciclovir leads through resistance genotyping, foscarnet toxicity, and ultimately to maribavir.

The Persistent Burn

Mycoplasma genitalium

Persistent urethritis in a young man after standard GC/CT treatment, with questions on microbiology, NAAT methodology, and resistance-driven sequential therapy.

The Plaque Before the Storm

Balamuthia mandrillaris

A facial skin lesion that foreshadowed a fatal encephalitis.

The Rainy Season Abscess

Burkholderia pseudomallei

A diabetic farmer, a draining wound, and a dangerous saprophyte.

The Report Said Susceptible

Klebsiella aerogenes

Bacteremic cholangitis caused by Klebsiella aerogenes with a deceptively susceptible-looking antibiogram and a cefepime SDD result that demands proper dosing.

The Ring in the Right Upper Lobe

Rhizopus arrhizus

A patient with uncontrolled diabetes and diabetic ketoacidosis has a right upper lobe reverse halo sign on chest CT.

The Rough Colony

Mycobacterium abscessus

A young man with cystic fibrosis develops progressive pulmonary infiltrates, constitutional symptoms, and subcutaneous nodules five months after bilateral lung transplantation.

The Shield Down the Drain

Streptococcus pneumoniae

Invasive pneumococcal disease as the first clue to an acquired immunodeficiency.

The Shoulder That Wouldn't Heal

Cutibacterium acnes

Subtle signs and a revealing gram stain lead to the diagnosis of an unusual shoulder infection. Master the key learning points for managing similar cases.

The Silent Swallow

Streptococcus anginosus, Prevotella melaninogenica

When aspiration writes a prescription for the brain.

The Summer Temporal Lobe Trap

La Crosse virus

A 17-year-old with summer encephalitis, temporal PLEDs, hyponatremia, and a negative routine CSF panel.

The Sweet Smell of Trouble

Streptococcus anginosus group, Streptococcus anginosus, Streptococcus intermedius, Streptococcus constellatus

Fever, weight loss, and a multiloculated liver abscess — with a blood culture plate that smells like butterscotch.

The Traveling Edema

Gnathostoma spinigerum

Migratory edema after raw seafood exposure.

The Ulcers That Would Not Heal

Herpes simplex virus type 1

A stem cell transplant recipient develops progressive mucocutaneous ulceration despite standard antiviral therapy.

The Unyielding Ring

Trypanosoma cruzi

Ring-enhancing brain lesions in an HIV patient from Bolivia that fail empiric toxoplasmosis therapy.

The Viscous Clue

Klebsiella pneumoniae

A diabetic man with endophthalmitis whose blood cultures revealed more than an eye infection.

The Waning Shield

Staphylococcus aureus, MRSA, VISA

A hemodialysis patient with MRSA bacteremia who fails to clear blood cultures on vancomycin — and the mechanism behind it.

The Water Was Warm

Naegleria fowleri

A previously healthy young man in Texas develops fulminant meningoencephalitis days after swimming in a warm lake, with anosmia and motile trophozoites on CSF wet mount.

The Watercress Fever

Fasciola hepatica

A Bolivian immigrant with fever, eosinophilia, and hepatic migratory lesions.

The Wheel Turns

Rotavirus

A nosocomial gastroenteritis outbreak on a surgical ward and a virus whose structure changes everything about how you contain it.

The Winter Breakthrough

Influenza A virus

Severe influenza A after allogeneic HSCT, with questions on viral entry, oseltamivir, and prevention.

The Wolf in CoNS Clothing

Staphylococcus lugdunensis

A destructive native-valve endocarditis caused by a coagulase-negative staphylococcus that should never be dismissed as a contaminant.

The Wrong Host

Toxocara canis

A young man with extensive tropical travel and dog shelter exposure presents with eosinophilia, hepatic lesions, pulmonary infiltrates, and a persistently negative stool exam.

Transient Leg Weakness in a Man from Rural Colombia

Taenia solium

Transient deficits, basal cistern lesions, and a hidden tropical diagnosis.

Two Continents, One Smear

Babesia microti

Fever, hemolysis, and intraerythrocytic ring forms in an asplenic traveler.

Undercooked

Toxoplasma gondii

A veterinary technician with steak tartare, two cats, and three weeks of fever and posterior cervical lymphadenopathy.

Verrucous Skin Lesions and a Right Upper Lobe Cavitary Opacity

Blastomyces dermatitidis

A verrucous arm lesion, diagnostic GMS stain, and right upper lobe pulmonary disease.

What Grew in the Scar

Mycobacterium kansasii

A retired gold miner with progressive massive fibrosis develops constitutional symptoms and a new right upper lobe cavitary lesion on CT.

When Ceftriaxone Fails

Enterococcus faecium

A cirrhotic patient develops persistent VRE bacteremia despite standard ceftriaxone prophylaxis, illustrating why Enterococcus faecium must be interpreted differently from Enterococcus faecalis.

When Mechanisms Collide

Escherichia coli, Enterococcus faecium, Candida glabrata

Three organisms, three kingdoms, and three antibiotic mechanisms of action tested in a single case of polymicrobial bacteremia from bowel perforation.

When molluscum is not molluscum

Talaromyces marneffei

Another skin lesion...

When the Back Pain Came Late

Mycobacterium bovis

A man develops delayed lumbar pain and constitutional symptoms long after intravesical BCG for urothelial carcinoma. Biopsy reveals granulomatous vertebral infection, and the next step depends on reading the clues correctly.

When the Fever Breaks

Dengue virus

A tropical febrile illness takes a dangerous turn.