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Treating curable sexually transmitted infections to prevent HIV in Africa: Still an effective control strategy?
Global Health Sciences Literature Digest
Published September 15, 2008
Journal Article

White RG, Orroth KK, Glynn JR, Freeman EE, Bakker R, Habbema JDF, et al. Treating curable sexually transmitted infections to prevent HIV in Africa: Still an effective control strategy? J Acquir Immune Defic Syndr 2008;47:346-53.

Objective

To investigate the cost-effectiveness of treating curable sexually transmitted infections (STIs) in preventing HIV transmission among different populations and at different phases of the HIV epidemic

Study Design

A computer model simulation study. The model STDSIM was fitted to the demographic, behavioral, and epidemiologic characteristics of four city populations in eastern and western Africa. STDSIM is an individual-based, stochastic model simulating the natural history and transmission of HIV and STIs in a population. It allows characteristics of individuals to change over time.

Setting

The characteristics of the populations of two east African, high HIV prevalence cities: Ndola, Zambia and Kisumu, Kenya, and two west African cities with low HIV prevalence: Cotonou, Benin and Yaounde, Cameroon were used in computer models that simulated the development of the HIV epidemic and the proportion of new HIV infections attributable to STI cofactor effects. These populations have been described previously. (1)

Primary Outcomes

The primary outcomes examined were the population-attributable fractions (PAFs) of incident HIV attributable to STIs, the impact of syndromic STI management on HIV incidence, and the cost per HIV infection averted compared with an estimate of lifetime HIV treatment costs in Africa (US$3500).

Results

The relative impact of improved syndromic STI case management on HIV incidence fell during the epidemics in all four cities. The simulated PAFs for combined STIs to HIV transmission ranged between 80-87% during years 4 to 5 of the HIV epidemics and between 50-70% in years 16 to 17. The PAFs for curable STIs, however, decreased during the HIV epidemics from 54-79% in years 4 to 5 to 13-33% during years 16 to 17 because of reductions in STI prevalence. But PAFs for HSV-2 increased during the HIV epidemics, with PAFs ranging from 8-27% in years 4 to 5 to PAFs ranging from 25-37% in years 16 to 17.

Syndromic STI treatment was predicted to be cost-effective in three of the four cities. Predicted cost-effectiveness varied between the four cities - US$321 in Ndola, $1499 in Kisumu, $1665 in Yaounde, and $4976 in Cotonou - making it cost-saving compared to the yearly treatment cost of US$3500 in all cities but Cotonou. Trends in the cost-effectiveness of the syndromic treatment intervention indicate that the estimated cost per infection averted was low 4 years into the epidemics but increased over time in all cities but Cotonou, where it remained high throughout the epidemic.

Simulating various levels of condom use showed that the cost-effectiveness of the intervention varied with varying levels and trends in condom use - as condom use increased, HIV and STI rates fell and the cost per HIV infection averted increased. These results indicate that in populations with high rates of male circumcision and low-risk sexual behaviors, syndromic treatment in the general population may not be cost-saving when condom use rises to >10-20% of casual contacts and >25-50% of sex worker contacts.

Conclusion

The authors concluded that throughout HIV epidemics in sub-Saharan Africa, a large proportion of HIV transmission may remain attributable to non-curable STIs but that the proportion attributable to curable STIs is likely to fall as the epidemic ages. In populations with generalized HIV epidemics, however, interventions that target curable STIs may remain highly cost-effective and even cost-saving if changes in risk behaviors have not adequately controlled STIs.

In Context

The evidence relating to the population-level impact of STI treatment on prevention of HIV transmission is not clear. One trial in Tanzania showed a significant reduction of HIV incidence in the general population as a result of syndromic STI treatment,(2) but four other trials have not shown any impact on HIV incidence.(3,4,5,6) This modeling study expands on other empirical and modeling work (1,7) that examined the heterogeneity of the HIV epidemic in various countries, especially levels of male circumcision and HSV-2 infection in the population, as a potential driver of the inconclusive impact of syndromic STI management on HIV incidence. Because HSV-2 is not a curable STI, syndromic STI treatment is not effective in reducing the PAF associated with HSV-2 infections.

Programmatic Implications

In African populations with mature HIV epidemics, STI treatment interventions are likely to remain highly cost-effective and potentially cost-saving, especially if safer sex has not adequately controlled STIs and the HIV incidence remains high.

References

  1. Orrroth KK, Freeman E, Bakker R, et al. Understanding differences across the contrasting epidemics in East and West Africa: results from a simulation model of the Four Cities Study. Sex Transm Infect 2007;83 (Suppl):i5-i16.
  2. Grosskurth H, Mosha F, Todd J, et al. Impact of improved treatment of sexually transmitted diseases on HIV infection in rural Tanzania: randomized controlled trial. Lancet 1995;346:530-536.
  3. Wawer Mh, Sewankambo BK, Serwadda D. et al, Control of sexually transmitted diseases for AIDS prevention in Uganda: A randomized community trial. Lancet 1999;353:525-35.
  4. Kamali A, Kinsman J, Nalweyiso N, et al. A community randomized controlled trial to investigate impact of improved STD management and behavioural interventions on HIV incidence in rural Masaka, Uganda: Trial design, methods, and baseline findings. Trop Med Int Health 2002;7:1053-63.
  5. Kaul R, Kimani J, Nagelkerke NJ et al. Monthly antibiotic chemoprophylaxis and incidence of sexually transmitted infections and HIV-1 infection in Kenyan sex workers: a randomized controlled trial. JAMA 2004;291:2555-62.
  6. Gregson S, Adamson S, Papya S, et al. Impact and process evaluation of integrated community and clinic based HIV-1 control: A cluster-randomised trial in Eastern Zimbabwe. PLoS Med 2007;4:e102.
  7. Buve A, Carael M, Hayes RJ, et al. The multicenter study on factors determining the differential spread of HIV in sub-Saharan Africa: methods and prevalence of HIV infection. AIDS 2001;15(Suppl 4):S5-14.