New criteria for immunofluorescence assay for Q fever diagnosis in Japan.
A study was made to evaluate the cutoff value of indirect immunofluorescent-antibody (IFA) test for Q fever diagnosis in Japan. We used 346 sera, including 16 from confirmed Q fever cases, 304 from Japanese pneumonia patients, and 26 from negative cases. Thirteen sera from the confirmed Q fever cases with an immunoglobulin M (IgM) titer of > or =1:128 and/or IgG titer of > or =1:256 by the IFA test were positive by both enzyme-linked immunosorbent assay (ELISA) and Western blotting assay (WBA), whereas 298 sera from pneumonia patients and 26 negative sera with an IgM titer of < or =1:16 and an IgG titer of < or =1:32 by the IFA test were negative by both ELISA and WBA. In the proposed "equivocal area," with an IgM titer of > or =1:32 and < or =1:64 and/or an IgG titer of > or =1:64 and < or =1:128, we found 9 sera, 3 from confirmed Q fever cases and 6 from Japanese pneumonia patients, by the IFA test. Three sera from the confirmed Q fever cases and one of the sera from pneumonia patients were IgM and/or IgG positive by both ELISA and WBA. These results suggest that a single cutoff value for the IFA test may cause false-positive and false-negative results. In conclusion, this study showed that an "equivocal area" should be used for the IFA test rather than a single cutoff value and that sera in the equivocal area should be tested by additional serological assays for confirmation.
Setiyono
A
A
Laboratory of Rickettsia and Chlamydia, National Institute of Infectious Diseases, 1-23-1 Toyama, Shinjuku-Ku, Tokyo 162-8640, Japan.
Ogawa
M
M
Cai
Y
Y
Shiga
S
S
Kishimoto
T
T
Kurane
I
I
D000907:Antibodies, Bacterial / Q000097:blood*; D016997:Coxiella burnetii / Q000276:immunology*; D005069:Evaluation Studies as Topic; D019084:Fluorescent Antibody Technique, Indirect; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood*; D007075:Immunoglobulin M / Q000097:blood*; D007564:Japan; D011778:Q Fever / Q000175:diagnosis*; D012698:Serologic Tests
D000907:Antibodies, Bacterial; D007074:Immunoglobulin G; D007075:Immunoglobulin M