Incidence and risk factors of C. trachomatis and N. gonorrhoeae among young women from the Western Cape, South Africa: The EVRI study.

Objective: Young women in South Africa are highly affected by sexually transmitted infections (STI), like C. trachomatis (CT) and N. gonorrhoeae (NG). We aimed to estimate the incidence of CT and NG, and its determinants, among young women from the Western Cape, South Africa, participating in an HPV vaccine trial (the EVRI study).

Methods: HIV-negative women aged 16-24 years were enrolled between October 2012 and July 2013. At enrolment and month 6 participants were screened for CT and NG (Anyplex CT/NG real-time detection method). A questionnaire on demographic and sexual history characteristics was completed at enrolment and month 7. Treatment for CT and/or NG was offered to infected participants. Incidence rates (IR) of CT and NG were estimated. Determinants of incident CT and NG infections were assessed using Poisson regression.

Results: 365 women were tested for CT and/or NG at least twice. Prevalence of CT and NG at baseline was 33.7% and 10.4%, respectively. Prevalence of co-infection with CT and NG was 7.1%. During 113.3 person-years (py), 48 incident CT infections were diagnosed (IR = 42.4 per 100 py, 95% confidence interval (CI) 31.9-56.2). Twenty-nine incident NG were diagnosed during 139.3 py (IR = 20.8 per 100 py, 95%CI 14.5-29.9). Prevalent CT infection at baseline was associated with incident CT (adjusted incidence rate ratio (aIRR) 5.8, 95%CI 3.0-11.23. More than three lifetime sex partners increased the risk for incident NG (3-4 partners aIRR = 7.3, 95%CI 2.1-26.0; ≥5 partners aIRR = 4.3, 95%CI 1.1-17.5).

Conclusions: The IR of bacterial STIs among young women in the Western Cape is very high. Besides being previously infected and a higher lifetime number of sex partners, no other risk factors were found for CT and NG, suggesting that the majority of these women were at risk. This indicates the need for intensified prevention of STIs as well as screening and treatment programs to increase sexual health in this region.