Figure 1

Model structure. Individuals enter the model on their 15^th birthday and exit on their 25^th birthday. All individuals entering the population are initially susceptible (S) to chlamydia infection, and enter each sexual activity class i (defined by partner contact rate c _i ) in proportions corresponding to the fraction of the population in each class (r _i ). The flows represent ageing into and out of the model (φ and α), and chlamydia infection (into CT), recovery (into R) and reinfection (into CT’). Infection rates for each sexual activity class are given by the force of infection, λ _i . In addition to natural recovery (δ), a proportion of individuals recover by seeking treatment (SEEKTREAT _INF * D _TREATED ), while further fractions recover through additional testing and treatment (COV * D _TREATED ), or by partner notification and treatment (PNe * POS _PN ) applied to treated index cases. A proportion of females (half of the model population) with incident infection develops PID, while a smaller proportion develops TFI. For a full explanation of the model structure see Methods text.