Clinical evaluation of CTS-1 specific coccidioidal immunodiffusion reagents for improved sensitivity and enhanced agreement with complement fixation testing.

INTRODUCTION: Coccidioidomycosis is a fungal infection endemic to the southwestern United States and northern Mexico. Laboratory evaluation often includes serological methods including enzyme immunoassays (EIA), immunodiffusion (ID), and complement fixation (CF). This study evaluated a newly available chitinase-1 (CTS-1) specific ID assay for serodiagnosis of Coccidioides infections.

MATERIALS AND METHODS: Sera from 1544 specimens were tested by traditional EIA, ID, CF assays, and simultaneously assayed using Cactus Bio CTS-1 ID reagents to compare the ability to identify seropositive patients. Positivity rates before and after implementing this CTS-1 specific ID, as well as agreement with CF results were measured.

RESULTS: Initial evaluation demonstrated 97.8% positive agreement and 86.9% negative agreement between new and reference ID assays. Reviewing cases of disagreement revealed that many positive ID results by this new method, but negative by reference ID, were on patients with history of coccidioidomycosis, suggesting increased sensitivity of the new ID test. Thus, results were reconsidered using ID, CF and recent history of positive results as the reference result. This improved positive and negative agreement to 98.6 and 95.7%, respectively. Furthermore, the high negative predictive value of this CTS-1 specific ID assay allowed for reflexive ordering patterns, reducing unnecessary testing of CF on negative patients.

CONCLUSION: This study demonstrates the effective use of Cactus Bio anti-CTS-1 ID for serodiagnosis of Coccidioides infections, which has been implemented as part of routine clinical care in our institution. Sensitivity and agreement with CF results are improved with this new testing strategy.