Proportion of Tubal Factor Infertility due to Chlamydia: finite mixture modeling of serum antibody titers

AE Ades, Malcolm Price, D. Kounali, V.A. Akande, G.S. Wills, M.O. McClure, P. Muir, PJ Horner

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This study examined whether the proportion of Tubal Factor Infertility (TFI) that is attributable to Chlamydia trachomatis, the population excess fraction (PEF), can be estimated from serological data using finite mixture modeling. Whole cell inclusion immune-fluorescence serum antibody titers were recorded in infertile women who were seen at St. Michael’s Hospital, Bristol, between 1985-1995 and classified as TFI cases or controls based on laparoscopic examination. Finite mixture models were used to identify the number of component titer distributions and the proportion of samples in each, from which estimates of PEF were derived. Four titer distributions were identified. The component at the highest titer was found only in samples from women with TFI, but there was also an excess of the second highest titer component in TFI cases. Minimum and maximum estimates of the PEF were 28.0% (95% credible interval: 6.9, 50.0) and 46.8% (95% Credible interval: 23.2, 64.1). Equivalent estimates based on the standard PEF formula from case-control studies were 0% and over 65%.
Finite mixture modeling can be applied to serological data to obtain estimates of the proportion of reproductive damage attributable to Chlamydia trachomatis. Further studies should be undertaken using modern assays in contemporary, representative populations.
Original languageEnglish
Pages (from-to)124–134
JournalAmerican Journal of Epidemiology
Issue number2
Early online date19 Jan 2017
Publication statusE-pub ahead of print - 19 Jan 2017


  • Tubal Factor Infertility
  • Chlamydia trachomatis
  • Population Excess Fraction
  • finite mixture models
  • antibody titres


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