Demographic and behavioural profile of adults infected with chlamydia: a case-control study

Objectives: To determine which demographic and behavioural parameters are i ndependently associated with chlamydial infection in adults. Methods: Subjects were recruited prospectively from male and female attende es at a large clinic for sexually transmitted infections (STI). All subject s were tested for chlamydia and gonorrhoea and asked to complete a question naire addressing demography, sexual and non-sexual (including drug taking) behaviour, and history of STI. Cases were those attending with a new clinic al episode and found to be infected with chlamydia, but who did not have go norrhoea. A control group was selected randomly from those found to be nega tive on screening for both infections. Results: 986 cases and 1212 controls were recruited over one calendar year. The following were found to be independent risk factors for chlamydial inf ection on multivariate analysis (odds ratios with 95% confidence intervals in parentheses): being unmarried (1.8; 1.1-3.1); black Caribbean ethnicity (2; 1.5-2.7). Increasing age, fewer partners, and higher reported use of co ndoms were associated with a lower risk of infection. Conclusion: Black Caribbeans are at increased risk from chlamydia after con trolling for sexual behaviour and socioeconomic status. Future research sho uld seek an explanation elsewhere-for example, in terms of differences in s exual mixing or effectiveness of healthcare interventions.