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Epidemiology poster session 3: Burden of disease
P1-S3.05 Attributable proportion of tubal factor infertility caused by chlamydia: an estimate based on serological evidence adjusted for test resolution
  1. M Price,
  2. A E Ades,
  3. J Macleod,
  4. P Horner
  1. University of Bristol, Bristol, UK

Abstract

Background Many published studies compare the prevalence of Chlamydia trachomatis (CT) antibody in women with Tubal Factor Infertility (TFI) and a control group. In principle these studies can be used to estimate the attributable fraction of TFI caused by CT, however it is necessary to account for the sensitivity and specificity of the antibody tests employed.

Methods We use sensitivity and specificity estimates from a discrepancy analysis by Morre (2002), and a study by Wills (2009) in which specificity of antibody test results was assessed in children, to derive estimates of the resolving power of three peptide-based assays and MIF; this is a reflection of the difference between sensitivity and false positive rates. Based on studies of antibody levels in different settings we adopt a model which assumes that antibody levels in women whose TFI is caused by CT are higher than levels in control women or those whose TFI has other causes. Applying this model to the data from Land (2003) we find strong support for the hypothesis of higher antibody levels in CT-related TFI, and for the estimates of test resolution from earlier studies. Using a range of assumptions about cumulative incidence of CT in the control group we were able to derive a range of estimates for the proportion of TFI cases caused by CT.

Results Our results suggest that the sensitivity of antibody tests in women whose TFI was caused by CT is higher than in women who have previously had CT but whose TFI was due to another cause and control women. Based on our estimates of the resolving power of the tests from the Morre (2002) and Wills (2009) studies we estimate the proportion of TFI episodes that are due to Chlamydia to be between 20% and 45%. Conclusions By adjusting for the sensitivity and specificity of tests it is possible to derive a quantitative estimate of the causal rate of CT in TFI. Taken together with other findings our results suggests that detailed studies of antibody levels can be used to shed further light on the causal rate of CT.

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