Background-This study was designed to rest the association of Chlamydi
a pneumoniae infection with asthma in a multiracial population, after
adjustments for several potential confounding variables. Methods-Antib
odies to C pneumoniae were measured by microimmunofluorescence in 123
patients with acute asthma, 1518 control subjects admitted to the same
hospital with various non-cardiovascular, non-pulmonary disorders, an
d 46 patients with severe chronic asthma, including some with ''brittl
e'' asthma, Acute infection or reinfection was defined by titres of Ig
G of greater than or equal to 512 or IgM greater than or equal to 8 or
a fourfold rise in IgG, and previous infection by IgG 64-256 or IgA g
reater than or equal to 8. Logistic regression was used to control for
likely confounders, including ethnic origin, age, sex, smoking habit,
steroid medication, diabetes mellitus and social deprivation, on anti
body levels. Results-Antibody titres consistent with acute C pneumonia
e infection were found in 5.7% of patients with acute asthma and 5.7%
of control patients, while 14.6% of patients with acute asthma and 12.
7% of control patients had titres suggesting previous infection. These
two groups did not differ significantly. However, titres suggesting p
revious infection were found in 34.8% of patients with severe chronic
asthma: the difference between this group and the control group was st
atistically significant with an adjusted odds ratio of 3.99 (95% confi
dence interval 1.60 to 9.97). Conclusions-These data raise important q
uestions about the previously demonstrated association of C pneumoniae
infection with asthma, and suggest that future studies of this associ
ation should give particular attention to the presence or absence of a
history of severe chronic asthma.