Clinical Features That Affect Indirect-Hemagglutination-Assay Responses to Burkholderia pseudomallei

Abstract

ABSTRACT Melioidosis, a disease endemic to northern Australia and Southeast Asia, is caused by the soil saprophyte Burkholderia pseudomallei . The indirect hemagglutination assay (IHA) is the most frequently used serological test to help confirm exposure to the causative organism. However, despite culture-confirmed disease, patients often have a negative IHA result at presentation and occasionally fail to seroconvert in serial testing. We retrospectively examined results for all patients with culture-confirmed melioidosis from our laboratory between January 1996 and August 2008. One hundred forty patients had a recorded IHA titer at presentation, 71 of which were positive at a titer of 1:40 or greater. Fifty-three patients went on to have subsequent IHAs 1 month or more after presentation. The relationships between IHA responses and clinical features were examined. The presence of bacteremia was significantly associated with a negative IHA at presentation. The coexistence of diabetes was associated with the presence of a positive IHA at presentation. In total, 14 patients (26%) demonstrated persistently negative IHA titers upon serial testing. No clinical factors were found to be significantly associated with this phenomenon. Supplementary testing using melioidosis-specific immunoglobulin G by EIA demonstrated different effects, with only Aboriginal or Torres Straits Islander ethnicity being significantly associated with a positive EIA at presentation. Reasons for these findings are examined, and directions for future research are discussed.