Discussion

In our study the only differences in sexual behaviour that distinguished Kisumu and Ndola from Cotonou and Yaoundoncerned the age at which girls became sexually active, and the age at which men and women first married. Compared with the low-prevalence sites, in Kisumu and Ndola females were younger at sexual debut and both sexes married earlier. In Kisumu, moreover, teenage girls whose husbands were older were more likely to be HIV-infected. High rates of partner change, contacts with sex workers, and concurrent sexual partnerships, were not reported more systematically in the high-prevalence than in the low-prevalence sites.

From these data, it would be difficult to argue that the divergence in the rate of HIV spread between the East African and West African sites can be explained solely by differences in sexual behaviour.

Nor was there evidence that differences in circulating strains of HIV-1 are a major factor in the rate of spread of HIV. Subtype A was the most prevalent subtype in both of the low-prevalence sites as well as in one high-prevalence site.

However, the study did find associations between higher HIV rates and two biological co-factors, suggesting that these might have contributed to a higher probability of HIV transmission during sexual intercourse in the high-prevalence sites.

Previous studies had already established that HIV transmission is enhanced in the presence of another STD, particularly an STD causing genital ulcers. The multi-site study found that significantly more people in Kisumu and Ndola, especially in the 15-24 age bracket, had serologic evidence of current or previous infection with an ulcerative STD (syphilis and genital herpes).

Secondly, the study found large differences between the sites in the percentage of men circumcised. In Cotonou and Yaoundcities where over 97% of men are circumcised, lower HIV rates were found than in Kisumu and Ndola, where the percentage of men circumcised ranges from 10% to less than 30%. In the high HIV prevalence sites, moreover, close to 16% of young men under 25 had an ulcerative STD, whereas in the low-prevalence sites the figure was 6%-8%. Lack of circumcision was thus associated with higher rates of both HIV and ulcerative STDs, the latter in turn possibly raising the HIV transmission risk.

Finally, how can one explain the dramatically high prevalence of HIV infection (15%-23%) in girls under 20 in Kisumu and Ndola? Unmarried girls in these cities reported a median of 1 to 1.5 lifetime sex partners, an estimated 10-12% of whom were HIV infected. A separate qualititative study carried out in Kisumu has found evidence of early sex with older partners (men aged 25 and above) among teenage girls, both married and unmarried. This suggests that the teenagers in the multi-site study may have under-reported their number of partners, especially non-spousal partners older than 25. Partners like these are likely to have exposed the girls to the virus, since HIV prevalence in Kisumu and Ndola among men aged 25 and over ranged from 26% to 40%.

Even when these factors are taken into account, however, it is hard to explain the high HIV prevalence in female teenagers. For the girls to have become infected so soon after their sexual debut as a result of relatively few exposures to an infected partner, HIV transmission co-factors must be part of the explanation. In this connection it is important to recall that almost 50% of the 15-19-year-old girls in Kisumu and Ndola had been exposed to the virus that causes genital herpes and almost 16% had syphilis.

In conclusion, differences in the rate of HIV spread between the East African and West African cities studied cannot be explained away by differences in sexual behaviour alone. In fact, behavioural differences seem to be outweighed by differences in HIV transmission probability.

The implications of our findings for the prevention measures are complex. For instance, if further studies prove that male circumcision is really protective, it would be important to assess carefully the benefits as well as the practical risks of the procedure under field conditions, including the risks of infection and haemorrhage. With respect to the ulcerative STDs, while syphilis is curable there are no drugs that can cure or reduce the transmission of genital herpes - a lifelong viral infection. Herpes can, however, be prevented through condom use, and research is in progress to develop a vaccine.

On the other hand, our findings should not be interpreted as a denial of the important role that sexual behaviour change and improved STD care can play in curbing the HIV epidemic. First of all, even the “low” HIV prevalence sites studied have considerable rates of HIV infection, and even in the high-prevalence sites barely a quarter of men reported that they often or always used condoms with non-spousal partners. The risk behaviours identified in all four sites call for scaled-up and sustained action in the areas of condom promotion, education for safer sexual behaviour, and diagnosis and treatment of the curable STDs.

Secondly, given the high levels of HIV infection in young women in Kisumu and Ndola, effective interventions are urgently needed to decrease their vulnerability. Girls must be made aware that they run an enormous risk of becoming infected with ulcerative STDs, HIV, or both, during their first few exposures to sex, especially with an older man, who is far more likely to be infected than boys their own age. Girls should learn the necessary life-skills to stand up to demands for early, unwanted or unsafe intercourse.

Above all, since men still play the dominant role in deciding whether and under what circumstances sex will take place, priority must be given to sexual behaviour change programmes aimed at them. Social pressure should be put on older men to avoid forcing or coercing young girls into sex, or enticing them with sugar-daddy gifts. Cross-generational sex exposes girls to lethal risk and helps drive the HIV epidemic.

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Members of the Study Group on Heterogeneity of HIV Epidemics in African Cities are: A Buvcoordinator), M Laga, E Van Dyck, W Janssens, L Heyndricks (Institute of Tropical Medicine, Belgium); S Anagonou (Programme national de Lutte contre le SIDA, Benin); M Laourou (Institut national de Statistiques et d’Analyses nomiques, Benin); L Kanhonou (Centre de Recherche en Reproduction humaine et en Dgraphie, Benin); Evina Akam, M de Loenzien (Institut de Formation et de Recherche dgraphiques, Cameroon); S-C Abega (Universitatholique d’Afrique Centrale, Cameroon); Zekeng (Programme de Lutte contre le SIDA, Cameroon); J Chege (The Population Council, Kenya); V Kimani, J Olenja (University of Nairobi, Kenya); M Kahindo (National AIDS/STD Control Programme, Kenya); F Kaona, R Musonda, T Sukwa (Tropical Diseases Research Centre, Zambia); N Rutenberg (The Population Council, USA); B Auvert, E Lagarde (INSERM U88, France); B Ferry, N LydiCentre frans sur la population et le dloppement, France); R Hayes, L Morison, H Weiss, J Glynn (London School of Hygiene & Tropical Medicine, UK); NJ Robinson (Glaxo Wellcome, UK); (M Cara(UNAIDS, Switzerland).

For more information, please contact Anne Winter, UNAIDS, (+41 22 791.4577)