Sexually transmitted infections increase risk of HIV transmission in serodiscordant couples - but don't fully explain high infection rates

It has been long hypothesised that early diagnosis and treatment of sexually transmitted infections may significantly reduce HIV transmission among HIV discordant couples. According to a study conducted in Africa and presented to the Sixteenth International AIDS Conference in Toronto on August 15th, HIV-negative individuals in a serodiscordant relationship who recently acquire a sexually transmitted infection are at increased risk of HIV seroconversion.

It is known that some sexually transmitted infections are associated with an increase of becoming infected with HIV. In Africa, couples where one partner is HIV-positive and the other HIV-negative have one of the highest incident rates for new HIV infections. Epidemiologic studies have found that in some African cities, approximately two-thirds of new HIV infections result from transmission within married or cohabitating couples. To measure the extent to which a sexually transmitted infection increased the risk of becoming infected with HIV, investigators from Rwanda and the United States gathered data on sexually transmitted infections, condom use and HIV seroconversion in a cohort of 1,590 serodiscordant couples.

Every quarter, the HIV-negative partners were tested for HIV and screened for the presence of a range of sexually transmitted infections, including syphilis, genital ulcerative disease, trichomonas, and penile discharge.

A total of 46 individuals seroconverted: 16 male-to-female infections in 763 couples and 30 female-to-male infections in 827 couples. Among the men, episodes of acute genital ulcers, positive RPR serology, cystitis, and urethral discharge were significantly more common in the three months prior to their seroconversion than in the prior quarterly testing intervals. The rates of these sexually transmitted infections were low, occurring in only 13-20% of the three months prior to their seroconversion.

In the women who seroconverted, only a diagnosis of cystitis was significantly more common in the three months interval before the positive than in the previous testing intervals (25% vs. 5.2%; p = 0.01).

The authors concluded that while they did see significantly more episodes of selected sexually transmitted infections in individuals prior to seroconversion, the relatively low incidence of sexually transmitted infections overall in this cohort is not sufficient to fully explain the majority of seroconversions.

Hence, most of the HIV infections appeared to occur in the absence of symptomatic sexually transmitted infections. The authors did admit that limited funding may have compromised the quality of some the sexually transmitted infections assays, namely accurate diagnosis of bacterial vaginosis.