Rapid detection of early typhoid fever in endemic community children by the TUBEX O9-antibody test.

Typhoid remains a global public health problem, and quick accurate immunodiagnosis is needed. Here, we examined the performance of the 5-min TUBEX O9-antibody detection kit in 243 outpatients (mostly children and infants) in their first week of fever and 57 healthy subjects in the Bangladesh community. Based on culture results, TUBEX was 91.2% (31/34) sensitive and 82.3% (172/209) specific in febrile subjects. However, specificity was better in nonfebrile healthy subjects (89.5%, 51/57) or in febrile individuals who serologically had dengue fever (90.5%, 57/63), suggesting that some culture-negative febrile individuals could be truly typhoidal. These individuals were also positive in an anti-crude O9 enzyme-linked immunosorbent assay (ELISA) and the Widal test. Regression analysis of the TUBEX and ELISA results showed good concordance between them, better with the combined IgM-IgG ELISA than with IgM alone, suggesting that TUBEX detects IgM antibodies not necessarily by themselves, as previously reported, but with the help of IgG antibodies.