Low and stable HIV infection rates in Senegal?

Meda and colleagues [1] reported on the low and stable rates of HIV prevalence in Senegal, and they concluded that Senegal has `contained the spread of HIV by intervening early and comprehensively to increase knowledge and awareness of HIV/AIDS and to promote safe sexual behaviour'. The data presented are impressive, for example the sequential seroprevalence data of pregnant women in Dakar in the period 1989–1996, which show no indication at all of an increase of HIV-1. The multi-pronged national response to the HIV epidemic is broad and far-reaching, and can serve as an example for other countries. We do have reservations, however, on the interpretations of some of the data. Our main worry is that the authors fail to distinguish sufficiently between HIV-1 and HIV-2. These are two different viruses, and although they share the same risk factors and transmission routes, the epidemiology and natural courses are markedly different [2]. Therefore, it does not seem justified to group the two infections together, as is done in Table 1 of their paper. The seemingly stable seroprevalence of all HIV combined may in reality mask a decline in HIV-2 and an increase in the incidence of HIV-1, a phenomenon that has been shown to occur in neighbouring Guinea-Bissau (O. Larsen, Z. da Silva, A. Sandstrom, et al., in preparation) [3]. The authors present graphs in which HIV-1 and HIV-2 are represented separately for Dakar, but this is not done for the three other sites. The trends in those sites can therefore not be assessed properly. Even if the distinction between the viruses is ignored, significantly upward trends in HIV prevalence are observed in two sentinel groups: femal sex workers (FSW) in Dakar (χ2 for trend 38.29, df = 3, P < 0.00001) and FSW in Ziguinchor (χ2 for trend 19.142, df = 3, P = 0.00001; data from Meda et al. [1], calculations ours). In male sexually transmitted disease (STD) patients in Ziguinchor there is a suggestion of an increasing trend (χ2 for trend 2.979, df = 3, P = 0.08). Senegal has legalized prostitution and this enables a more successful public health policy in this high-risk group. However, the authors estimate that perhaps as many as 50% of FSW are not registered. The non-registered FSW are likely to be less exposed to health education messages, to have less access to appropriate care for STD and condoms, and therefore to be more at risk of HIV. The non-registered FSW are not tested routinely for HIV. This selection bias is likely to lead to an underestimate of the true prevalence of HIV, and it is therefore doubtful whether the suggested recent plateauing of HIV prevalence among FSW is real. The authors mention that in a cohort of 997 registered FSW in Dakar the HIV-1 incidence was 1.1 per 100 person-years of observation between 1985 and 1995, and that there was no evidence of an increase in incidence (P = 0.07). This conclusion contrasts strongly with an earlier report on this cohort, which demonstrated a significant 12-fold rise in the risk of HIV-1 infection between 1985 and 1992, or a 1.4 increased risk for every subsequent calendar year [4]. A more recent update documented the increase of HIV-1 seroincidence from 0 in 1985 to 3.9 per 100 person-years of observation in 1996 [5]. In conclusion, we applaud the comprehensive approach taken in Senegal in response to the HIV epidemic. However, it is doubtful whether the data are indeed evidence of a halted HIV-1 epidemic in Senegal. In order to show that, prevalences should be given separately for HIV-1 and HIV-2. Acknowledgements The authors would like to thank Olav Larsen for sharing unpublished data, and Shabbar Jaffar for helpful comments on a draft version. Maarten F. Schim van der Loeff Tumani Corrah Hilton C. Whittle