A seroepidemiologic study of Chlamydia pneumoniae in Rhode Island. Evidence of serologic cross-reactivity.

OBJECTIVE

Although Chlamydia pneumoniae is considered a common cause of pneumonia worldwide, the evidence is mainly serologic. Therefore, we examined whether the currently used chlamydial microimmunofluorescence (MIF) antibody test is specific for C pneumoniae infection.

DESIGN AND SETTING

Secondary analysis of data from a cohort study of sarcoidosis among the graduates of ten consecutive apprenticeship classes of firefighters and police officers.

PARTICIPANTS

One hundred forty-seven young adult men.

MEASUREMENTS

Immunoglobulin G and M antibodies to C pneumoniae, 15 serovars of C trachomatis, and 2 strains of C psittaci as measured by MIF.

RESULTS

Evidence of previous C pneumoniae and C trachomatis infection (IgG > or = 1:16 yet < 1:512) was present in 108 (73 percent) and 59 (40 percent) subjects, respectively. Serologic evidence of recent C pneumoniae and C trachomatis infection (IgM > or = 1:16 or IgG > or = 1:512) was present in 19 (13 percent) and 14 (10 percent) subjects, respectively. Chlamydia pneumoniae and C trachomatis IgM titers were highly correlated (r = 0.80; 95 percent CI, 0.73 to 0.85) while C pneumoniae and C trachomatis IgG titers were fairly correlated (r = 0.44; 95 percent CI, 0.30 to 0.56).

CONCLUSIONS

The C pneumoniae seroprevalence of 86 percent is the highest yet reported. The correlations between C pneumoniae and C trachomatis antibody titers suggest that chlamydial MIF may be less specific than is generally appreciated. Moreover, the observed 13 percent seroprevalence of recent C pneumoniae infection in a healthy working population challenges the serologically based belief that this agent accounts for 6 to 10 percent of community-acquired pneumonia. A more objective, more specific test is needed in the serodiagnosis of C pneumoniae infection.