Very little is known about the natural course of C
pneumoniae infection in general. When does infection first occur?
Is it always associated with illness? How long can it persist?
Seroepidemiologic studies7–8 suggested that C
pneumoniae infection occurs primarily in school-aged children and
the prevalence of infection increases with increasing age. Following
the criteria proposed by Grayston et al,9 acute infections
were defined by a fourfold rise in IgG titer between consecutive
specimens or a single IgM titer of ≥ 16 or a single IgG of ≥ 512.
An IgG titer ≤ 256 was considered to indicate past exposure. However,
subsequent studies4,10 that have utilized culture and PCR
for detection of C pneumoniae suggest that infection may
occur at earlier ages than implied by MIF serology. The most
interesting observation was the lack of correlation between positive
culture results and serology; approximately 70% of culture-positive
children in these studies were MIF negative, and < 5% met the
serologic criteria for acute infection.,10 Hyman et
al3 reported that 18% of a group of culture-negative,
subjectively healthy adults met the serologic criteria for acute
infection with a single serum sample, IgG ≥ 512 and/or IgM ≥ 16.
Two subjects in this study3 had nasopharyngeal swab
specimens that were culture positive and/or PCR positive; one subject
was seronegative and one subject had an IgG titer of 256 in a single
serum specimen. The results of other studies11–13 in
adults suggest that some high anti-C pneumoniae IgG antibody
detected by MIF may be heterotypic, either due to infection with other
chlamydial species or other organisms, including Bartonella and
Bordetella pertussis. Chlamydial heat shock protein
(HSP) 60 is almost identical to that of Escherichia
coli,14 and a recent study15 found
picornavirus proteins also share antigenic determinants with
HSP60/HSP65, including C pneumoniae HSP60.