Study confirms cost-effectiveness of STI management in HIV control

In sub-Saharan Africa, the management of sexually transmitted infections (STIs) remains a cost-effective strategy for controlling HIV in a number of different scenarios, report an international team of researchers in the March 1^st edition of the Journal of Acquired Immune Deficiency Syndromes. Even in mature epidemics with substantial condom use, their study found that more than half of new HIV infections may be attributable to STIs.

Previous research conducted in Mwanza, Tanzania, of syndromic management of STIs - treatment of presenting symptoms according to guidelines - showed that STI treatment was cost-effective in reducing HIV incidence. However, later African trials failed to find a reduction in HIV incidence with such management.

Investigators from the London School of Hygiene and Tropical Medicine suggested that “this may be because behavior change and the later stage of the HIV epidemic reduce the role of curable STIs in HIV transmission”. These findings have led some policy makers to question the role of STI treatment in tackling generalised epidemics of HIV in Africa.

A multi-centre study published in 2001 identified two East African cities with high HIV prevalence and two West African cities with relatively low HIV prevalence. Notably, the prevalence of male circumcision was lower and the prevalence of herpes simplex virus-2 (HSV-2) was higher in the cities with higher HIV prevalence. However, sexual risk behaviours were not consistently higher in the West African cities, and modelling confirmed that the different prevalence rates were largely explainable by biologic factors, mainly male circumcision.

Investigators extended this work to evaluate the proportion of new HIV infections attributable to STIs (population-attributable fraction) and the impact of syndromic STI treatment.

The investigators used a known statistical model to simulate the natural history and transmission of HIV and STIs between individuals. The simulation has previously been used and found to agree with data from large, randomised trials.

Data from the Tanzanian trial were used as a basis to simulate the effect and costs of STI treatment. Factors such as condom usage and STI treatment effects were then varied to model different scenarios. The potential impact on HIV prevalence was modelled from the presumed start of the HIV epidemic in each city for 16-20 years, until 2000-01.

The simulated impact of STIs on HIV incidence was 80-87% during years four to five of the epidemics, and remained high at 50-70% in years 16-17.

While the impact of curable STIs fell over time, the impact of HSV-2 rose, which explains why the effect of STI treatment decreased over time.

However, the authors write that “the absolute impact of syndromic management remains high in generalized epidemics, and it remained cost-saving in three of the four populations in which the cost per HIV infection averted ranged between US $321 and $1665”.

These figures are lower than the estimated lifetime cost of treating HIV infection in these areas, at around $3500. In the fourth city, STI treatment might not be cost-effective due to the relatively low prevalences of curable STIs and the low incidence of HIV.

The authors further suggest that in cities with low rates of male circumcision and relatively high-risk sexual behaviours, STI treatment may be cost-effective even with condom usage as high as 30-37.5% of casual contacts and 45% of sex worker contacts or higher. STI treatment is virtually always cost-effective if HIV prevalence was above 5.5%, they report.

However, in other scenarios, STI management has “important collateral public health benefits, which effectively protects patients with STIs from the enhanced risk of HIV acquisition and transmission,” the team concludes.