Chlamydia pneumoniae respiratory tract infection: the interpretation of high titres in the complement fixation test

Sera from 5 acute respiratory disease patients from Northern Norway presenting with high chlamydia complement fixation (CF) titres, were analyzed for Chlamydia pneumoniae-specific IgG and IgM in a micro-immunofluorescence (micro-IF) test that included antigens from the prototype strain TW 183, and a Norwegian isolate, FML 10. The patients were confirmed to have had C. pneumoniae infection based on serologic findings. This establishes the clinical significance of early CF results in this geographical area. However, different micro-IF titres against the 2 C. pneumoniae isolates tested suggest antigenic variability among the species.