Higher Risk Behavior and Rates of Sexually Transmitted Diseases in Mwanza Compared to Uganda May Help Explain HIV Prevention Trial Outcomes

Three large-scale community randomized trials in East Africa found different results regarding STD treatment as an intervention to prevent HIV transmission. In Mwanza, Tanzania, syndromic STD case management reduced HIV incidence by 38 percent in the general population, suggesting that the treatment of genital ulcer and discharge syndromes could be an effective HIV control strategy in African populations. However, STD mass treatment trials in Rakai, Uganda, and trials of a behavioral intervention in conjunction with syndromic STD treatment in Masaka, Uganda, showed little or no effect on HIV incidence.

The authors undertook the current study to determine to what extent differences in the trial outcomes might be explained by differing STD epidemiology, sexual risk behavior and demographic risk factors in the three populations. The researchers compared baseline data from the Mwanza, Rakai and Masaka trial populations using standardized indicators and definitions after adjusting for differences in data collection methods.

The researchers found that demographic patterns were similar across populations. Mwanza had higher sexual risk behaviors, including younger age of sexual debut, higher number of recent partners and lower frequency of condom use than either Rakai or Masaka.

HIV epidemiology at the start of the three trials showed major differences among the sites. HIV prevalence was highest in Rakai (16.5 percent), lower in Masaka (12.1 percent) and lowest in Mwanza (3.8 percent). The Ugandan sites have a more mature HIV/AIDS epidemic than Mwanza.

Age and sex patterns of HIV prevalence were similar across sites except for differences in overall levels. Prevalences were higher for females than males, peaking between 25-29 years for women and 30-34 years for men. Age peaks were somewhat younger in Mwanza than in the Ugandan sites, consistent with the relatively young epidemic in Mwanza, where the majority of prevalent cases have been contracted recently.

The authors noted the higher prevalence of short-duration, curable STDs in Mwanza and higher rates of risky sexual behavior reported at that site. Most differences among the sites related to markers of recent risk rather than past risk, suggesting that risky behavior may have decreased in the recent past in Uganda.

For instance, high-titer serological syphilis, reflecting recent risk behavior, was more prevalent in Mwanza than in Uganda. However, all titer serological syphilis was more prevalent among older participants in Rakai and Masaka than Mwanza, suggesting past rather than current risk behavior. Gonorrhea, chlamydia and trichomoniasis were all more prevalent in Mwanza. Seroprevalence of Herpes simplex virus type-2 differed little among sites.

"Our findings of higher risk sexual behavior and STD prevalences in Mwanza than in Rakai and Masaka may help to explain why STD reductions reduced HIV incidence in Mwanza, but had little effect in Rakai or Masaka," the researchers concluded. "We would theoretically expect a larger impact of STD treatment interventions and behavioral interventions in populations in which reductions in risky sexual behavior have not yet taken place and in which prevalences of curable STDs are high. For generalized epidemics in which behavioral change may have already occurred, interventions to prevent HIV transmission in stable relationships become much more important. Such interventions might include voluntary counseling and testing with disclosure to partners, vaginal microbicides, consistent condom use by HIV-discordant couples, male circumcision, HSV-2 suppression, vaccines and antiretroviral therapy."

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