Objectives: To test the association of Chlamydia pneumoniae infection with ethnic origin.
Design: A prospective study by micro-immunofluorescence of antibodies to C. pneumoniae in patients admitted to one hospital with a variety of non-pulmonary, non-cardiovascular disorders.
Setting: A large district general hospital serving a multi-ethnic inner-city population in Birmingham, UK.
Subjects: There were 1518 patients, 1061 of whom were Caucasian, 290 Asian and 167 Afro-Caribbean. Each of 169 Asians and 141 Afro-Caribbeans was matched with two Caucasians for age, sex, smoking habit, steroid medication and date of admission, and logistic regression methods were used to compare the effects on C. pneumoniae antibody levels of ethnic origin, these confounding variables, diabetes mellitus and social deprivation.
Outcome measures: Serological evidence of acute C. pneumoniae infection or reinfection (defined by titres of IgM > or = 8, a four-fold rise in IgG or IgG > or = 512) and previous infection (IgG 64-256 or IgA > or = 8).
Results: Results showed 4.8% of Caucasians, 6.6% of Asians and 10.2% of Afro-Caribbeans had antibody titres suggesting acute (re)infection; and 11.2% of Caucasians, 13.4% of Asians and 21.0% of Afro-Caribbeans had titres suggesting previous infection. On chi 2 analysis, the distributions of the three possible serological outcomes (acute, previous and no infection) differed significantly (p < 0.05) between the Afro-Caribbean and Caucasian groups, but not between Asians and Caucasians or between Afro-Caribbeans and Asians. After adjusting for possible confounding variables, odds ratios for Afro-Caribbean versus Caucasian origin were 5.5 (95% confidence intervals 2.0-15.0) for acute (re)infection and 1.9 (1.0-3.7) for previous infection.
Conclusions: Our results suggest that C. pneumoniae infection may be more prevalent among Afro-Caribbean than among Caucasian people, and that Asians may lie somewhere between them in this respect. The behaviour of this pathogen in different ethnic groups deserves further investigation. Future studies of this organism should give due attention to the ethnic origins of patients.