Diagnosing Fungal Causes of Community-Acquired Pneumonia: Guidance From the CDC and MSGERC

Coccidioidomycosis, histoplasmosis, and blastomycosis are underrecognized fungal infections that can present as community-acquired pneumonia (CAP), with symptoms similar to bacterial or viral pneumonias. The Centers for Disease Control and Prevention (CDC) and Mycoses Study Group Education and Research Consortium (MSGERC) released guidelines on when and how to test for fungal etiologies of pneumonia.

Patients with CAP who have an epidemiologic link to an outbreak of coccidioidomycosis, histoplasmosis, or blastomycosis should be tested for the relevant fungal pathogen.

Testing for coccidioidomycosis is recommended for patients who present with CAP or erythema nodosum with recent respiratory symptoms who live in regions where coccidioidomycosis is highly prevalent. These areas include south-central Arizona and the San Joaquin Valley in California.

Testing should be considered for patients with apparent CAP with continued symptoms after empiric antibiotic treatment if they live in or have traveled to an area where coccidioidomycosis is prevalent. This includes Arizona, California, Nevada, New Mexico, Texas, Utah, and Washington as well as Central and South America.

A serum enzyme immunoassay (EIA) antibody test should be obtained initially. If available, immunodiffusion and complement fixation testing should be included because they have greater specificity than EIA antibody testing alone, but these can add to cost.

Positive test results should lead to treatment, whereas negative results make an alternative diagnosis more likely than coccidioidomycosis. If clinical suspicion remains high, symptoms progress, or symptom onset is recent, repeating serology in 2 to 6 weeks, obtaining sputum or bronchoalveolar lavage culture and microscopy, or consulting an infectious disease or pulmonary specialist should be considered. Polymerase chain reaction testing has low sensitivity and can only be performed on tissue samples. Antigen testing should be used in immunocompromised patients with a negative serum antibody test.

Testing for histoplasmosis should be considered in patients with CAP who have a history of exposure to bird or bat droppings or a chest radiograph showing a new nodule or lymphadenopathy consistent with histoplasmosis. Rheumatologic symptoms such as myalgias and arthralgias as well as dermatologic findings of erythema nodosum or erythema multiforme can be present and should prompt testing.

The guidelines recommend testing for histoplasmosis in patients with CAP whose symptoms do not improve with antibiotics and who live in or have traveled to an area where histoplasmosis is prevalent. These regions include the Central and Eastern United States, with the highest prevalence in the Ohio and Mississippi river valleys and the Great Lakes region. Histoplasmosis is also found in eastern Central and South America, the Caribbean, central Europe, southern Africa, and Southeast Asia.