[Discussion of positive initial infection criteria for Chlamydophila (Chlamydia) pneumoniae in children: IgM antibody titers by ELISA compared to micro-IF and Western blotting].

Microimmunofluorescence testing (micro-IF) is a standard serological test Chlamydia pneumoniae (C. pneumoniae) infection, but requires sophisticated techniques. ELISA, a simple, easy diagnostic method, has thus come into wide use and is included by the National Insurance System of Japan as an approved and reimbursable procedure. Based on Kishimoto's criteria, initial C. pneumoniae infection is diagnosed by ELISA at single serum IgM antibody titer in children ID > or = 1.10, adult ID > or = 1.60. The positive percentage of C. pneumoniae IgM antibody in children, however, is unexpectedly high, and the antibody level has been found to remain positive for several months or more. In an effort to revise positive criteria for initial infection with C. pneumoniae, we compared IgM antibody titer of ELISA to that of micro-IF and Western blotting (WB) in acute pediatric respiratory tract infection. Specimens were collected from 128 children with acute respiratory tract infection; 106 (11-months to 14-year-olds) with an IgM antibody ID > or = 1.10 and 22 (8-months to 12-year-olds) with an ID < 1.10. The 77 samples with an ID > or = 1.40 of IgM antibody by ELISA included 4 negatives in micro-IF and 8 negatives in WB. Regarding definitive cases as C. pneumoniae-IgM positive by both micro-IF and WB, the receiver operating characteristic curve showed that the optimal value was ELISA ID 1.40; sensitivity 86.8%, specificity 96.3%, the positive predictive value 98.5%, and the negative predictive value 72.2%. Diagnostic precision in initial C. pneumoniae infection in children may therefore be improved by revising positive criteria of ELISA IgM titer.