Background STI may be markers of at-risk sexual behaviours, and in persons with HIV probably also increase infectiousness and risk of HIV transmission, even with viral suppression by antiretroviral drugs (ARV). However, estimates of STI in this group have proved problematic, and there are few longitudinal studies able to accurately measure incidence.
Methods In 2010, we established a cohort of individuals from ten sexual health clinics that were already enrolled in AHOD. We calculated diagnosis rates for four STI (Chlamydia, gonorrhoea, infectious syphilis, anogenital warts) from 2005–2010, and true incidence rates from 2010–2011.
Results At baseline (2010), the cohort (n = 520) did not differ markedly from the rest of AHOD(n = 1668). There was a gradual increase in chlamydial infections, from 3.4/100person-years(py) (95% CI 1.9–5.7) in 2005, to 6.7/100py (95% CI 4.5–9.5) in 2011, with a substantial peak in 2010, 8.1/100py (95% CI 5.6–11.2). The cases were evenly distributed between urethral (49%) and rectal (51%) infections. Similarly, gonococcal infections increased, with a peak in 2010 (4.7/100py, 95% CI 5.6–11.2), but rectal (63%) outnumbered urethral (37%) infections. Infectious syphilis showed several peaks, the largest in 2008 (5.3/100py, 95% CI 3.3–8.0). The incidence of genital warts declined from 7.5/100py in 2005 (95% CI 4.8–11.3) to 2.4/100py in 2011 (95% CI 1.1–4.5).
Conclusions The incidence of chlamydial and gonococcal infections, and infectious syphilis was higher than previous estimates in Australia. The incidence of genital warts was lower. Ongoing incidence data will assess relationships between STI, HIV-viral load, immunodeficiency, ARV and STI treatment, and patient characteristics.
- Prospective cohort