Poor Sensitivity of a Rapid Kit for Diagnosing Scrub typhus: Need for Continuous Monitoring and Regular Quality Check Type of Article: Brief Communication

Abstract

In many parts of India, clinical diagnosis of Scrub Typhus (ST) is confirmed by Rapid Immunochromatographic Test (RICT) and/or IgM ELISA. Our aim was to decide the suitability or otherwise of SD Bioline Tsutsugamushi rapid kit due to discrepancies we observed since January 2015. Sera from 30 clinically and laboratory confirmed ST cases and 30 controls were examined by SD Bioline and ST InBios IgM Rapid, keeping ST IgM InBios ELISA as reference. Two different lots of SD Bioline kits picked up same seven patients (23.3% sensitivity) whereas InBios IgM Rapid identified all 30 ST patients. Healthy controls were negative by both RICT and ELISA kits. Although specificity of SD Bioline kit was 100%, the sensitivity was very low (23.3%). Batch to batch variation may be a manufacturing defect or due to poor storage/transport conditions. Regular monitoring of the rapid kits is essential to avoid false negativity/positivity.

Keywords

• immunochromatographic test
• scrub typhus
• st rapid elisa