Chlamydial Pneumonitis and Its Serodiagnosis in Infants

Abstract

Sera from 30 infants with suspected chlamydial pneumonitis were studied by enzyme immunoassay (EIA) with three antigens: reticulate bodies (RB), purified major outer membrane protein (MOMP) of Chlamydia trachomatis strain L₂, and purified lipopolysaccharide from Re mutants of Salmonella (Re LPS), which shows complete crossreaction with chlamydial glycolipid. The immunofluorescence test (I/RB IFAT), which detected IgM antibodies (titer of ≥1:64) in 16 patients whose clinical picture was consistent with chlamydial pneumonitis, was the standard method. EIA measured IgM antibodies to the purified antigens but not to RB; 15 sera were positive with the MOMP antigen and two with the Re LPS antigen. High-titered IgG antibodies were detected by I/RB IFAT in 15 and by MOMP EIA in 13 of the 30 sera. By the RB EIA, 17 sera were positive. The MOMP EIA was thus as sensitive and specific as the I/RB IFAT. Because the EIA can be automated, it would make possible the screening of all children younger than six months of age with respiratory-tract symptoms and IgM antibodies to Chlamydia.