Comparative evaluation of a commercial enzyme immunoassay for the detection of human antibody to Rickettsia typhi.

A commercial enzyme immunoassay kit called the Dip-S-Ticks (DS) for the detection of total immunoglobulin (Ig) G and IgM human antibodies to Rickettsia typhi was evaluated. In tests with 340 serum samples from patients with diagnosed cases of rickettsial diseases, patients suffering from other febrile illnesses, and normal subjects, the DS compared favorably with the standard indirect fluorescent-antibody (IFA) test. At IFA cutoff titers of > or = 1.64 and > or = 1:128, the DS showed sensitivities of 88.2 and 91.4% and specificities of 91.8 and 87.7%, respectively. The DS test correlated significantly with both the IFA IgG (r = 0.84, P < 0.0005) and IgM (r = 0.63, P < 0.0005) titers. Only 80% of IgG and 82% of IgM IFA readings determined by two technicians were within one dilution, while the DS was more reliable, with 100% within one dot. The rapidity, reliability, and simplicity of the DS suggest that it is a suitable test for use in clinical laboratories unable to perform the IFA test.