Comparative evaluation of four serodiagnostic tests for scrub typhus in Thailand

The commercial dot-blot enzyme-linked immunosorbent assay Dip-S-Ticks dipstick test was compared with the indirect immunoperoxidase (IIP) and Weil-Felix (WF) tests for the diagnosis of scrub typhus, using the indirect immunofluorescent antibody test (IFA) as the reference standard. With a panel of 117 positive and 75 negative sera, the dipstick test was 94% sensitive and 98.7% specific at a cut-off value of one or more positive dots. The IIP was 90.6% sensitive and 100% specific at a cut-off titre of 1:400, and was more sensitive than the IFA with acute sera (79.6% vs. 68.5% at a titre > or = 1:400). All 3 were superior to the WF, which lacked sensitivity. The dipstick assay was easy to perform and did not require sophisticated electrical equipment, and the results were available within one hour. It is therefore suitable for use in rural Thailand, where scrub typhus is common.