The opportunists and invaders · every high-yield organism in one drill
Opening Challenge
An HIV-positive patient (CD4 count 45) presents with severe headache, fever, and neck stiffness over 5 days. CSF shows elevated opening pressure. India ink prep reveals encapsulated yeast with narrow-based budding. Cryptococcal antigen positive. Organism and correct induction treatment?
A) Aspergillus fumigatus: voriconazole monotherapy
B) Cryptococcus neoformans: liposomal amphotericin B + flucytosine
C) Candida albicans: fluconazole
D) Histoplasma capsulatum: itraconazole
Cryptococcus neoformans, ampho B + flucytosine. India ink shows the clear halo of the polysaccharide capsule. Narrow-based budding distinguishes it from Blastomyces (broad-based). In AIDS with CD4 below 100, Crypto is the most common cause of fungal meningitis. Induction: liposomal ampho B + flucytosine x2 weeks. Consolidation: fluconazole 400mg x8 weeks. Maintenance: fluconazole 200mg indefinitely. High ICP managed with serial LPs. Break it down: CD4 <100 + India ink halo + narrow-based budding + positive cryptococcal antigen = Cryptococcus neoformans meningitis; induction = liposomal ampho B + flucytosine x2 weeks; consolidation = fluconazole 400mg x8 weeks; maintenance = fluconazole 200mg indefinitely; serial LPs manage dangerously high ICP.
01 · Geography
Where the Dimorphics Hide
Geography is the first clue. Tap each region to see which organism dominates.
Dimorphic Rule
❄
25°C (cold lab)
MOLD form
Branching hyphae
↔
🩹
37°C (body temp)
YEAST form
Round budding cells
Memory: Mold in the Cold, Yeast in the Beast. Exception: Coccidioides makes spherules with endospores at 37°C (not true yeast).
01 · Organisms
Know the Pattern, Name the Bug
Tap any card to expand. Filter by type or immune status.
Host
01B · High-Yield Villains
The Board Killers
Tap to flip. Geography, clue, host, drug, board move on the back.
Why these 7? These are the organisms that appear in vignettes most. Know the clue that triggers each one before the stem ends.
🦠
Histoplasma
Dimorphic Fungus
Tap to reveal
Geography
Ohio + Mississippi River Valleys · bat/bird droppings, spelunking
Key Clue
Macrophages packed with intracellular oval yeast on Wright/Giemsa stain
Dimorphic rule: Mold in the cold (25°C), yeast in the beast (37°C). Exception: Coccidioides makes spherules with endospores, not true yeast.
Organism
Geography / Source
Unique Clue
At-Risk Population
Histoplasma
Ohio + Mississippi Valleys
Bat/bird droppings, spelunking
HIV (disseminated), spelunkers
Blastomyces
Great Lakes + SE United States
Soil, decomposing organic matter
Hunters, trappers, campers
Coccidioides
SW United States (San Joaquin, Arizona)
Desert soil, dust storms
Filipinos, African Americans (disseminated)
Paracoccidioides
Latin America (Brazil)
Soil, outdoor workers
Males, rural farm workers
Sporothrix
Worldwide (plants, soil)
Rose thorns, sphagnum moss
Gardeners, florists
Cryptococcus
Worldwide (pigeon droppings)
India ink clear halo, narrow-based budding
HIV CD4 <100, transplant
Aspergillus
Worldwide (ubiquitous conidia)
Halo sign on CT, septate 45-degree
Neutropenic, asthma/CF
Mucor/Rhizopus
Worldwide (soil, decaying matter)
Black palate necrosis, non-septate 90-degree
DKA, deferoxamine use
Helminth drug cheat sheet: Ivermectin (Strongyloides, Onchocerca, Scabies) · Praziquantel (Schistosoma, all tapeworms) · Albendazole (most nematodes, neurocysticercosis + steroids) · DEC (Wuchereria) · Mebendazole (intestinal nematodes alternative)
03 · Elimination Game
Narrow It Down
Use clues to eliminate wrong answers. One organism survives.
Scenario 1 of 3
04 · Quiz
Pattern Recognition
Clinical vignettes. Every wrong answer gets a mechanism-based explanation.
Question 1 of 6Ring-enhancing brain lesion in an AIDS patient with CD4 count of 68. Multiple lesions concentrated in the basal ganglia. Serum Toxoplasma IgG is positive. Lumbar puncture is deferred due to herniation risk. What is the most appropriate next step?
AStart fluconazole for cryptococcal meningitis
BBrain biopsy to confirm organism before treatment
Question 2 of 6A 55-year-old man with DKA is admitted after 3 days of facial pain and right-sided periorbital swelling. Exam shows black necrotic eschar on the hard palate and right proptosis. CT confirms right orbital invasion. What is the correct immediate treatment?
AStart fluconazole empirically
BLiposomal amphotericin B + urgent surgical debridement
CStart voriconazole for invasive mold
DObserve; this appears to be severe bacterial sinusitis
Question 3 of 6An HIV-positive patient with CD4 count of 85 presents with 3 weeks of profuse watery, non-bloody diarrhea. Stool acid-fast stain shows small acid-fast oocysts. The patient is not on antiretroviral therapy. What is the most effective intervention?
AMetronidazole
BNitazoxanide
CInitiate antiretroviral therapy for immune reconstitution
DPraziquantel
Question 4 of 6A 48-year-old man from rural Bolivia presents with progressive dysphagia, constipation, and exertional dyspnea. Echo shows a dilated cardiomyopathy with EF 30%. Barium swallow reveals megaesophagus. He grew up in a home with thatched walls and roofing. What is the vector and causative organism?
Question 5 of 6A 34-year-old man with HIV and CD4 count of 48 presents with 3 weeks of progressive dyspnea, non-productive cough, and low-grade fever. Chest X-ray shows bilateral diffuse interstitial infiltrates. LDH is 520 U/L. SpO2 is 88% on room air. What is the correct treatment?
AVoriconazole for invasive mold
BTMP-SMX + prednisone
CLiposomal ampho B + flucytosine for Cryptococcal disease
DAzithromycin for atypical pneumonia
Question 6 of 6A 28-year-old aid worker returns from 6 months in Guatemala with 2 weeks of bloody diarrhea, crampy abdominal pain, and tenesmus. Stool O&P reveals trophozoites containing ingested red blood cells. LFTs are normal. What is the correct treatment?