Background
Sexually transmitted infections (STI) may directly increase the risk of HIV infection, or may indicate sexual practices that increase the risk of HIV infection. In persons with HIV they probably also increase the infectiousness of HIV, even in the context of treatment with antiretroviral drugs (ARV). Estimating STI in this group has proved problematic, and there are few longitudinal studies able to accurately measure incidence.
Methods
In 2010, we established a cohort of individuals from ten widely dispersed sexual health clinics that were already enrolled in the Australian HIV Observational Database (AHOD). We calculated retrospective diagnosis rates for four STI (chlamydia, gonorrhoea, infectious syphilis, anogenital warts) from 2005-2010, and prospective incidence rates from 2010-2011.
Results
At baseline (2010) , the patient characteristics (n=554) were similar to the rest of AHOD (n=1767), namely they were predominantly male, homosexual, middle-aged, and pre- treated with ARV. Overall, the incidence of any STI was 12.5/100 person years (py). There was a gradual increase in chlamydial infections , from 3.4/100 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 of 8.1/100py (95% CI 5.6-11.2) in 2010. The cases were distributed between rectal ( 61.9%), urethral (34%), and pharyngeal (6.3%) sites. Similarly, gonococcal infections increased, with a peak in 2010 of 4.7/100py (95% CI 5.6-11.2), (p value for trend=0.0099), distributed between rectal (63.9%), urethral (27.9%), and pharyngeal (14.8%) sites. Infectious syphilis showed several peaks, the largest in 2008 (5.3/100py , (95% CI 3.3-8.0), but the overall trend was not significant (p=0.113). Diagnoses of genital warts declined from 7.5/100py (95% CI 4.8-11.3) in 2005 (95% CI 4.8-11.3) to 2.4/100py (95% CI 1.1-4.5) in 2011 (p value for trend=0.0016).
Conclusions
The incidence of chlamydial and gonococcal infections in this cohort was higher than previous estimates in Australia among HIV-infected men who have sex with men (MSM), and increased during the 2005-2011 study period. Rectal infections greatly outnumbered infections at other sites. The incidence of infectious syphilis remained high, but did not increase, and the incidence of genital warts was lower, and decreased. These are the first measurements of STI incidence among persons being treated for HIV in Australia. They may underestimate the true incidence of these infections in the HIV-infected population.