Effects of periodic presumptive treatment on three bacterial sexually transmissible infections and HIV among female sex workers in Port Moresby, Papua New Guinea

Background: Sexually transmissible infections (STI) are common in female sex workers (FSW). Aim: To determine if 3-monthly periodic presumptive treatments (PPT) would reduce the prevalence of STI in FSW. Methods: In a cohort study conducted between November 2003 and September 2004, FSW were enrolled, counselled and interviewed. Informed consent was obtained. Testing by using polymerase chain reaction (PCR) for Chlamydia trachomatis (Ct), Neisseria gonorrhoeae (Ng) and Trichomonas vaginalis (Tv), and serology for HIV were performed at baseline and final follow-up visits. Each FSW received 3-monthly oral amoxicillin, probenecid, a combination of amoxicillin and clavulanic acid, and azithromycin. Tinidazole was administered once. Results: The cohort consisted of 129 FSW at baseline and 71 at final follow-up visit. Of these 71 FSW, there was a significant decline in the proportion with positive PCR results for Ct from 38% to 16% (P = 0.001), Ng from 56% to 23% (P = <0.001) and Tv from 62% to 30% (P = <0.001) between baseline and the final follow-up visit. HIV prevalence increased from 15% to 21% (P = 0.125). Conclusions: PPT was statistically effective in reducing STI but rates rebounded rapidly. Several new HIV infections occurred. If PPT is to be very effective in FSW where the prevalence of STI is so high, then 100% condom use with clients and regular sexual partners (RSP), and high rates of notification of RSP would be required if low incidence and prevalence of STI were to be achievable.