Risk factors for chlamydial infection in chlamydia contacts: a questionnaire-based study

Treatment of individuals with chlamydial infection and their sexual partners is an important aspect of reproductive health care. Partners of infected individuals are currently offered 'epidemiological treatment', which means that they are offered antibiotic treatment at their first visit without waiting for the result of their chlamydia test. We carried out a study to identify the risk factors for chlamydial infection in partners of infected individuals. Individuals attending a genitourinary clinic as chlamydia contacts were identified and asked to complete a questionnaire about their relationship with the index case and their prior sexual history. The result of their chlamydia test was then analysed against those variables.

A total of 115 chlamydia contacts were analysed in this study; 60 (52%) were found to be positive for chlamydial infection. In a multivariate analysis, young age, more than one episode of sexual intercourse with the infected partner and a greater total number of sexual partners were associated with a positive chlamydia result. A prediction model for chlamydial infection using these risk factors had a discriminatory ability quantified by an area under the curve (AUC) of 0.76 (95% CI 0.66-0.85).

The risk factors identified can be used when discussing epidemiological treatment with individuals who attend sexual health services as chlamydia contacts, or to target clinic resources to a higher-risk group. Larger studies will be necessary to assess the benefits and risks of changing to a policy of offering epidemiologic treatment to 'high-risk' contacts only, identified using a predictive model such as the one described here.