Background Chlamydia trachomatis (CT) is an important risk factor for the development of Pelvic Inflammatory Disease (PID), but despite much study the extent of its causal role remains unclear. Knowledge of the role of Chlamydia is critical for assessing the cost-effectiveness of screening programmes.
Methods We perform a Bayesian multi-parameter synthesis of evidence from a range of prospective, retrospective, and routine data sources. These were; randomised trials following screened and unscreened women to PID; retrospective studies of Chlamydia in PID cases and controls, from which an etiologic fraction can be estimated; routine data on the number of PID cases diagnosed in England in 1 year; survey data on the probability of diagnosis of PID. We also used information on the incidence and prevalence of CT in England and the clearance rate of asymptomatic infection.
Results We found that the different data sources provided consistent estimates of the critical parameters. We estimate the probability an episode of Chlamydia causes an episode of PID to be 0.09 (0.04 to 0.16) and that the Excess fraction of PID cases due to Chlamydia to be 0.20 (0.09 to 0.35). We estimate that prior to the start of the current screening program in the UK the annual population incidence of PID in women in England was 0.022 (0.016 to 0.028) in women aged 16−24 and 0.013 (0.009 to 0.019) in women aged 25−44 and that 42% (31% to 54%) of these cases were diagnosed.
Conclusions In the absence of direct data, it is possible to statistically combine evidence from different types of data, to check the consistency of the data sources, and to estimate the relation between CT and PID. In considering the effect on PID risk of treating women who screen positive for Chlamydia, it is important to note that this is a survivor population who acquired CT an unknown time previously and who have not developed PID.