Seroprevalence of IgG antibodies against Chlamydia pneumoniae in Chinese, Malays and Asian Indians in Singapore.

Background: Chlamydia pneumoniae, a bacterium that causes respiratory infections, is probably under-diagnosed. There is also interest in its possible role in the aetiology of coronary heart disease. This is the first population-based seroprevalence survey of C. pneumoniae infection in Singapore.

Methods: A random sample of 1,068 people aged 18-69 years was selected from the participants of the Singapore National Health Survey conducted in 1998. Sera and data on certain clinical measurements and conditions had been collected. IgG antibodies for C. pneumoniae were detected using an indirect microimmunofluorescence test and positivity graded. Seropositivity was defined as IgG titre >/=1:16.

Results: There were no statistically significant differences in the prevalence rates of seropositivity to C. pneumoniae for age group 18-69 years among the three ethnic groups, i.e. Chinese (males 76.7%, females 68.3%), Malays (males 75.4%, females 59.1%), and Asian Indians (males 74.6%, females 59.4%). The seropositivity rate for people aged 18-69 years in Singapore was 75.0% for males and 65.5% for females (difference of 9.5%, P < 0.001). In both genders combined, seropositivity increased from 46.5% in the age group 18-29 to reach a plateau of 78.9% in the age group 40-49, which remained stable to 60-69 years. There was no association of seropositivity with smoking, diabetes mellitus, hypertension or body mass index after adjustment for age and gender.

Conclusion: The high prevalence rates in our study population and the higher rate in males compared to females are consistent with studies from other parts of the world. No significant difference in prevalence rates was observed among Chinese, Malays and Indians. The pattern of rising and levelling off of seropositivity with age suggests that C. pneumoniae infection occurs early in life, and in older ages the high level of seropositivity is probably maintained by re-infections or chronic infections. Chlamydia pneumoniae infection was not found to be associated with the cardiovascular risk factors examined.