Development and evaluation of a latex agglutination test for the rapid diagnosis of scrub typhus.

The purpose of this research was to develop a simple and rapid diagnostic test for scrub typhus using a latex agglutination test (LAT) to detect antibodies against Orientia tsutsugamushi. Five strains of O. tsutsugamushi were propagated in L929 cells. The rickettsiae were purified and concentrated with percoll density gradient centrifugation. A suitable concentration of O. tsutsugamushi soluble antigen was used to sensitize latex to prepare the latex antigen. The specificity, sensitivity, and accuracy of the latex antigen were assessed. The LAT, indirect immunofluorescent antibody test (IFA), and Weil-Felix agglutination test (WF) were compared by testing 109 acute febrile illness cases and 100 confirmed non-scrub typhus cases (50 other febrile disease cases and 50 healthy controls). By using the IFA as the standard reference method, the overall sensitivity, specificity, and accuracy of the LAT were 89.1, 98.2, and 93.6%, respectively. By contrast, the sensitivity of the WF, compared with the IFA, was only 47.3%, while the specificity and accuracy were 92.6 and 69.7%, respectively. Thus, the LAT described here is another important alternative test for the diagnosis of scrub typhus.