Serological tests for blastomycosis: assessments during a large point-source outbreak in Wisconsin

Area of Science:

• Medical Microbiology
• Immunology
• Infectious Diseases

Background:

• Blastomycosis is a significant fungal infection requiring accurate diagnostic methods.
• Serological tests like immunodiffusion (ID) and complement fixation (CF) have limitations in detecting Blastomyces dermatitidis antibodies.
• Evaluating novel diagnostic approaches is crucial for effective disease management.

Purpose of the Study:

• To assess the efficacy of enzyme immunoassay (EIA) compared to ID and CF tests for detecting Blastomyces dermatitidis antibodies.
• To evaluate EIA as an epidemiological tool during a blastomycosis outbreak.
• To determine the diagnostic and suggestive antibody titer thresholds for EIA.

Main Methods:

• Enzyme immunoassay (EIA), immunodiffusion (ID), and complement fixation (CF) tests were performed on serum samples.
• Samples were collected from 47 patients with confirmed blastomycosis and 89 control subjects.
• Antibody detection rates, titers, specificity, and timing relative to illness onset were analyzed.

Main Results:

• EIA detected antibodies in 77% of patients, significantly higher than ID (28%) and CF (9%).
• EIA showed high sensitivity, detecting antibodies missed by ID and CF, with titers ranging from 1:8 to 1:512 (median 1:128).
• EIA specificity was 92%, with 8% of controls showing low positive titers (1:8 or 1:16).

Conclusions:

• EIA represents a significant advancement in the serodiagnosis of blastomycosis.
• EIA is a valuable epidemiological tool for identifying acute Blastomyces dermatitidis infections during outbreaks.
• EIA titers ≥1:32 strongly support a blastomycosis diagnosis, while titers of 1:8 or 1:16 are suggestive.