Results are similar for cohabiting couples. In all but one country the unadjusted odds of one or both partners being HIV infected are two to seven times greater among couples in the highest wealth quintile than among those in the lowest wealth quintile. Adding controls for selected underlying factors, proximate factors, and community-level wealth progressively diminishes the strength of this association. With all factors controlled for, the odds of one or both partners being HIV infected remain greater than one in six out of the eight countries considered, but statistically significant at the 5% level in only one country (Tanzania).
This study found that, contrary to evidence for other infectious diseases and theoretical expectations, HIV prevalence is not disproportionately higher among adults living in poorer households in sub-Saharan Africa. In all eight countries included in the present analysis, wealthier men and women tend to have a higher prevalence of HIV than poorer individuals. In most cases, the positive association between wealth status and HIV is considerably diminished when a number of underlying factors (such as education, urban/rural residence, and community wealth) and some of the behavioural and biological pathways (proximate factors, such as sexual risk taking, condom use, and male circumcision) are taken into account. The results indicate that much of the positive association between wealth and HIV is caused by these underlying or mediating factors. Even after accounting for these various factors, however, in most countries wealthier adults remain at least as likely as poorer individuals to be infected with HIV, if not more. The results are similar for cohabiting couples.
Our analysis indicates that several factors may be responsible for the observed higher HIV prevalence among wealthier individuals in these countries. First, the wealthier are more likely to live in urban areas and to live in wealthier communities, where HIV is more prevalent. Wealthier adults, especially men, tend to be more mobile, more likely to have multiple partners, and more likely to engage in sex with non-regular partners, behaviours that tend to be associated with a higher HIV prevalence. On the other hand, wealthier men and women tend to be more educated and have a greater knowledge of HIV prevention methods. As such, they may be more likely to receive healthcare, to use condoms (both with non-regular partners and consistently with all partners), and less likely to use alcohol when having sex. Wealthier men are more likely to be circumcised, which may reduce their risk of HIV infection. Also, wealthier adults may live longer with HIV than poorer individuals as a result of their better health and nutritional status.
Women are less likely than men to report having multiple partners and non-regular partners. We found that the positive association between wealth status and HIV prevalence tends to be stronger for women than for men in most countries, suggesting disproportionately greater vulnerability of women in the wealthier groups.
There are several limitations of this study that should be kept in mind when interpreting our findings. One important limitation is that DHS/AIS surveys do not collect data on household income or expenditure, which would traditionally be included in an assessment of wealth status. The assets-based wealth index used here is only a proxy indicator for household economic status . In addition, wealth index scores cannot be compared across countries both because the level and distribution of wealth differs from one country to another and because the choice of assets included in the construction of the index varies somewhat from country to country. In spite of these issues, in developing-country settings, the wealth index has been shown to produce superior results and equal or greater distinctions in health outcomes than household expenditure-based measures . Moreover, as income and expenditure measures can be volatile and temporary, wealth status (which results from the accumulation of income) is a preferred measure to relate to HIV prevalence (which results from an accumulation of incidence).
A second limitation is differential non-response in the surveys considered. Non-response rates for HIV testing tend to be higher among the wealthier, urban, and more educated adults, who also tend to have higher HIV prevalence. Previous research has, however, indicated that in these surveys differential non-response has small and insignificant effects on the observed HIV prevalence, so any bias caused by differential non-response by wealth status should be small . In any case, if there were no differential non-response by wealth status, the positive association between wealth status and HIV prevalence would be even stronger. In addition, the surveys considered exclude population groups that are difficult to locate or interview, most notably the homeless. The observed positive association between wealth status and HIV prevalence may be overestimated to the extent that the homeless are poorer and have higher HIV prevalence than those included in the survey. Given that the proportion of the homeless in the total population tends to be small, any effect of excluding this group on the observed associations is likely to be small.
Another limitation is that our analysis is based on self-reported behaviours. There is evidence that women tend to underreport and men tend to exaggerate their premarital and extramarital sexual activity . Epidemiological studies in Africa have also observed weak associations between self-reported risky sexual behaviour and HIV status . The findings of our study may be biased to the extent that men and women misreport their number of sexual partners, sex with non-regular partners, condom use, and other related behaviours, or to the extent that the degree of misreporting is different across the wealth quintiles.
A fourth limitation is that the surveys included in the analysis did not collect data on concurrent partnerships and sexual networks. We were thus unable to examine the extent to which wealthier individuals are more likely to engage in such complex patterns of sexual relations, which may increase the risk of HIV infection in Africa by allowing the virus to spread rapidly to others [41–45].
Moreover, because of the cross-sectional nature of the data used in this study, endogeneity might bias our results at several levels. First, when considering the effect of wealth status on HIV prevalence we do not allow for the opposite, detrimental effect of HIV infection on wealth status, which is well established [46,47]. Excluding HIV-positive individuals who reported being seriously ill for three or more months in the previous 12 months (in Tanzania, Uganda, Cameroon, and Malawi, where such information was collected) had virtually no effect on the observed associations between wealth and HIV status (data not shown). Second, if HIV-positive adults were aware of their serostatus, they might have adjusted their sexual and reproductive behaviour. We tested this by excluding HIV-positive individuals who were previously tested and received the result, which made little difference to the observed associations between wealth and HIV status (data not shown). Third, when infected with HIV, wealthier individuals are likely to survive longer than poorer individuals because of better nutrition and access to healthcare. Cross-sectional data used in this study did not allow taking into account such selective survival of wealthier respondents. A lack of information on the availability and access to treatment and care (antiretroviral drugs in particular) further limited the possibility of disentangling this effect. Antiretroviral therapy coverage was, however, still very low at the time of the survey data collection in most countries.
In conclusion, this study found a positive association between household economic status and HIV prevalence among adult men and women in sub-Saharan Africa. Accounting for various underlying factors and proximate determinants explains much of this positive association, but in most cases wealthier adults remain at least as likely as poorer individuals to be HIV infected. We found that HIV prevalence does not follow the same pattern of association with poverty within countries in sub-Saharan Africa as most other diseases. Although poverty reduction is an essential strategy to improve health and combat the HIV epidemic, our analysis suggests that HIV prevention, care, and treatment programmes should also be focused on the better-off segments of the population. Focusing on the most important modes of exposure will probably be more effective than focusing broadly on poverty reduction [49,50]. It will also be important to extend programmes to the rural areas where a majority of the population in sub-Saharan Africa resides.
It is important to stress that our findings do not imply that the poor are not disproportionately affected by HIV when they do get infected. Poverty reduction is an extremely important goal in itself for many reasons, and it will certainly help combat the HIV epidemic in the long run and deal with its many adverse consequences.
The authors wish to thank the numerous people who provided comments on the two presentations and on earlier drafts of this paper.
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