How Much Tubal Factor Infertility Is Caused by Chlamydia? Estimates Based on Serological Evidence Corrected for Sensitivity and Specificity

Objectives: To estimate the proportion of tubal factor infertility (TFI) caused by Chlamydia trachomatis (CT), the etiologic fraction, from a retrospective study of CT antibody prevalence in TFI cases and controls, adjusted for sensitivity and specificity. Methods: We use published data on sensitivity and specificity to estimate the performance of assays in (a) women with a previous CT infection without sequelae and (b) women with TFI caused by CT. A model was developed and applied to antibody prevalence in TFI cases and controls from 1 published case-control study to estimate the proportion of TFI caused by CT. Results: The proportion of TFI episodes that were due to CT infection was estimated to be 45% (credible intervals: 28%, 62%). Models which assume that test sensitivity is higher in women with CT-related TFI than women with previous infection and no sequelae fit the data significantly better than models that assume the same sensitivity in all those previously infected. Conclusions: Greater attention needs to be paid to methods for characterizing the performance of CT antibody tests. Serological studies could be given a greater role both in CT etiology and in monitoring the effects of prevention and control programmes.