# Blastomyces Urine Antigen Testing for Active Case Identification During a Blastomycosis Outbreak

## TL;DR

Urine antigen testing helped find new blastomycosis cases during an outbreak, including some asymptomatic cases.

## Contribution

The study shows urine antigen testing can identify new and asymptomatic blastomycosis cases during outbreaks.

## Key findings

- Urine antigen testing identified 25 previously undetected blastomycosis cases.
- 10% of employees with positive test results were asymptomatic.
- Urine antigen testing was well accepted by employees and effective in finding additional cases.

## Abstract

Blastomyces urine antigen testing is a sensitive blastomycosis diagnostic method, but its utility for active case identification during outbreaks is unknown. We evaluated urine antigen testing for identifying blastomycosis cases during a 2023 outbreak at a Michigan, USA, paper mill and assessed demographic and clinical factors associated with test positivity. Approximately 2 months after the outbreak was recognized, we collected work and health information for 603 employees; 95% (n = 578) underwent urine antigen testing and 9% (n = 52) tested positive, including 25 previously undetected cases. Blastomycosis-like symptoms were associated with test positivity (p<0.001), but 10% of employees with positive results were asymptomatic. Recent hospitalization for blastomycosis was associated with test positivity (p = 0.02) and higher antigen levels. Further research into urine antigen testing is needed clarify its suitability for detecting mild and asymptomatic infections during outbreak investigations. Urine antigen testing had high acceptability among employees and effectively identified additional cases.