Figure 1.

A, Mathematical model for Ct and Mgen infection and recovery, used to synthesize evidence. Women move between states according to a susceptible-infected-susceptible (SIS) model of natural history, with per-capita infection rates alphaSC (Ct) and alphaSM (Mgen) and recovery rates alphaCS (Ct) and alphaMS (Mgen). Neither infection affects the acquisition or recovery rate of the other. There is a “background” rate of developing PID, alphaSP, and rates attributable to Ct and Mgen infection, alphaCP and alphaMP respectively. B, PID rates per 100 000 women, predicted by our model using Ct and Mgen prevalence in 4 age groups in Natsal-2 (Ct) and Natsal-3 (Mgen). The prediction includes a correction to allow for the fact that only women with PID who are diagnosed (estimated to be 55% of those with symptoms; see Methods) are recorded in surveillance data. Point markers and error bars show posterior medians and 95% credible intervals, adjusted for the fraction of cases presenting for medical care; numbers are given above the plot. Circles indicate all cases, upward-pointing triangles Ct-attributable cases, and downward-pointing triangles Mgen-attributable cases. Density plots around the all-cause predictions show the sampled posterior distributions. Dashed lines indicate upper and lower bounds for PID rate observed in surveillance in 2002 reported by Price et al [5], adjusted for the proportion of women who were sexually active in each age group. Abbreviations: Ct, Chlamydia trachomatis; Mgen, Mycoplasma genitalium; Natsal, National Survey of Sexual Attitudes and Lifestyles; PID, pelvic inflammatory disease; +, positive; –, negative.