Should a person with potential exposure to histoplasmosis, possibly having a weakened immune system or underlying health conditions, be tested for the infection?

Testing for Histoplasmosis After Exposure

Most people exposed to someone with histoplasmosis do NOT need testing because histoplasmosis is not transmitted person-to-person—it requires inhalation of fungal spores from contaminated soil or bird/bat droppings. 1, 2

Critical Distinction: Histoplasmosis Is NOT Contagious Between People

• Histoplasmosis infection occurs exclusively through inhalation of airborne Histoplasma capsulatum spores from environmental sources (soil contaminated with bat or bird excrement), not from person-to-person contact 1, 3, 4
• Being around someone with histoplasmosis poses no transmission risk unless you share the same environmental exposure source 3, 4

When Testing IS Indicated: Shared Environmental Exposure

Testing should be pursued if the exposed person shared the same environmental source (cave exploration, construction site, bird roost area, moldy environment) as the infected individual, particularly if they develop symptoms or have risk factors. 1, 5

High-Risk Populations Requiring Lower Threshold for Testing:

• Immunocompromised patients: HIV/AIDS with CD4+ counts <150 cells/μL, organ transplant recipients, patients on chronic corticosteroids or TNF-alpha inhibitors 1, 2, 6
• Patients with underlying lung disease: Those with centrilobular emphysema or structural lung defects 1, 6
• Extremes of age: Very young children or elderly patients 1, 2

Testing Algorithm Based on Clinical Context

For Symptomatic Patients (Fever, Cough, Chest Pain, Fatigue):

Immunocompetent patients:

• Order Histoplasma antibody testing (serology) as the primary test, with 80-95% sensitivity for pulmonary histoplasmosis 1, 5
• Consider adding urine and serum Histoplasma antigen if symptoms are severe or progressive, as combined testing increases sensitivity to 93-96% 1

Immunocompromised patients:

• Order Histoplasma antigen testing (urine AND serum) as the primary diagnostic approach, with 95% urine sensitivity and 85% serum sensitivity for disseminated disease 1
• Do NOT rely on antibody testing in immunocompromised patients—sensitivity drops to only 18% in transplant recipients and 45% in HIV/AIDS patients 1, 5

For Asymptomatic Patients with Shared Environmental Exposure:

Immunocompetent individuals:

• Observation without testing is appropriate for most asymptomatic immunocompetent persons, as acute pulmonary histoplasmosis is self-limited in the majority of cases 1, 6
• Consider testing only if symptoms develop and persist beyond 1 month 1, 6

Immunocompromised individuals:

• Lower threshold for testing with Histoplasma antigen (urine and serum) even if asymptomatic, given the high risk of progressive disseminated disease 1, 2, 6
• Testing is particularly important if the patient has CD4+ count <150 cells/μL or is an organ transplant recipient 1, 2

Key Testing Caveats

• Cross-reactivity: Histoplasma antigen tests cross-react with blastomycosis, coccidioidomycosis, paracoccidioidomycosis, and talaromycosis—clinical correlation with geographic exposure is essential 1, 5
• Timing matters: Antibody testing requires weeks to become positive after initial exposure, limiting utility in acute presentations 1, 5
• Endemic area background: In Ohio and Mississippi River valley residents, positive serology may reflect remote exposure rather than active disease 5

When Treatment Is Indicated Regardless of Testing

If testing confirms infection, treatment decisions depend on severity and immune status:

• Immunocompetent patients with mild symptoms: Observation without treatment is appropriate if symptoms resolve within 1 month 1, 6
• Immunocompetent patients with symptoms >1 month: Itraconazole 200 mg daily for 6-12 weeks 1, 6
• Any immunocompromised patient with confirmed histoplasmosis: Treatment is mandatory regardless of symptom severity, starting with amphotericin B for severe disease or itraconazole for mild disease 1, 2, 6