Chlamydia pneumoniae: Risk factors for seropositivity and association with coronary heart disease

Two studies have suggested that seropositivity for Chlamydia pneumoniae (C. pneumoniae) is a risk factor for coronary heart disease (CHD) but the association remains tenuous. Further data is required in other populations to consolidate this observation. Initially to determine descriptive risk factors for C. pneumoniae seropositivity in a general population sample and subsequently to examine the relation of seropositivity for this organism to CHD for the first time in a British population. A single general practice health screening clinic and a cardiology clinic involving patients predominantly residing in south London and Surrey. 210 consecutive caucasian men (62%) and women (38%) aged 18–79 including 67 men aged 45–65. This latter group acting as controls were then also compared with 103 consecutive males aged 45–65 with angiographically confirmed coronary heart disease. A questionnaire was administered by a research nurse and serum was analysed for IgG and IgA against C. pneumoniae and other Chlamydiae by a microimmunofluorescence test. Serum was said to be low positive at a specific IgG antibody titre of 16–32, and high positive if 64 or greater. Amongst the general practice health screening clinic population 14 subjects (7%) were excluded due to possible cross-reactivity with other Chlamydia species (predominantly C. trachomatis). Of the remaining 196 subjects, 13 (6%) had high positive C. pneumoniae IgG titres, 68 (35%) had low titres and 1.25 had no detectable antibody. After adjustment for sex, age, smoking history, social class and family size only one risk factor for high positive titres in this group was identified, which was the number of children currently living in the home (OR 2.29 1.09–4.80, P = 0.03). No factors were significantly related to low titres. 22/100 (22%) cases with coronary heart disease and 3/64 (4.7%) of controls had high positive IgG titres for C. pneumoniae. Similarly 21% of cases and 9.4% of controls had positive C. pneumoniae specific IgA serology. 45% of cases and 44% of controls had low C. pneumoniae IgG titres. The association of CHD with a C. pneumoniae IgG titre of 64 or above was independent of all risk factors (OR 7.4 (1.7–33.1), P