Estimating the effects of accelerated partner therapy (APT) on reinfection of index cases with chlamydia: a mathematical modelling study

ABSTRACT Objectives The expected effects of accelerated partner therapy (APT) on the reinfection of treated index cases by untreated partners with Chlamydia trachomatis (chlamydia) remain unclear. We analyzed data from the LUSTRUM cluster cross-over randomised controlled trial (RCT) using a mathematical model and quantified the effects of offering APT on the probability of successful partner treatment. Methods We extended a previously developed mathematical model to compute the probability of chlamydia reinfection of index cases by their untreated partners with chlamydia. We fitted the model to data from the RCT and estimated the probability of successful treatment of the partner of index cases using a Bayesian framework. Results We estimated the median probability of reinfection with chlamydia at 16.3% (50% credible interval, CrI: 12.7-20.0%) without partner treatment and 2.3% (50% CrI: 1.7-3.6%) when partner treatment is 100% successful. The observed rates of reinfection in the RCT were 6.7% (95% confidence interval, CI: 5.6-8.0%) during the control period (standard partner notification (PN)) and 4.8% (95% CI: 3.7-5.9%) during the intervention period where APT was offered in addition to standard PN. These rates correspond to a median probability of successful partner treatment of 63% (50% CrI: 47-76%) during the control period and 78% (50% CrI: 65-87%) during the intervention period. Conclusions Our study suggests that the observed reduction in reinfection with chlamydia when offering APT is consistent with a higher probability of successful partner treatment.