Lack of Association Between Concurrency and HIV Infection

To the Editors: Kasamba et al1 make a common mistake in studying the association between concurrent partnerships and HIV status: they test for associations that are not predicted by the concurrency hypothesis or not appropriate given their cross-sectional study design. The former is unique to the study of concurrency and the latter reflects a failure to follow general principles of epidemiological inference. The authors have data on both partners (spouses), which is one of the requirements for estimating the impact of concurrency, but they have data on prevalent, not incident, HIV infection. Although the investigators correctly characterize the risk concurrency poses for partners, their data do not allow accurate estimation of this risk. This compromises every association they test between HIV status (of husband, wife, and couple) and the husband's extraspousal partnerships. First, with respect to the association between a husband's concurrency in the last year and his HIV status (Tables 2 and 3 in Kasamba et al), the fundamental problem is that the concurrency hypothesis does not predict an association between husband's concurrency and his HIV status. His risk is simply a function of his cumulative number of partners and unprotected coital exposures with each. Whether his partners are concurrent or serial, his risk is the same. However, testing the association of his recent behavior with his prevalent infection is an additional problem. Second, with respect to the association between the HIV status of the couple and the husband's concurrency, the discrepancy between the timeframes of infection and behavior is the key problem. Recent behavior (in this case, concurrency in the 12 months before the survey) may have nothing to do with a prevalent infection in one or both members of the couple because that infection that may have been contracted many years earlier. Third, the authors test for an association between the wife's HIV status and the husband's extraspousal partnerships, and conclude “despite the hypothesis that concurrency would lead to a likelihood of transmission to sexual partners, we do not find evidence that women whose husbands report having extra-spousal partnerships are at greater risk of HIV infection.” The problem is that the concurrency hypothesis does not predict this association in a cross-sectional study, and what the hypothesis does predict—increased incidence in the husband, and then the monogamous partner—is not measured by this study. Table 1 illustrates the conditions needed for proper causal inference when using HIV prevalence here: concurrency can only be inferred as potentially responsible for the wife's infection when HIV prevalence is observed in a couple that began their partnership concordant negative. Even then, one would need to rule out the possibility that the wife also may have been infected from an extraspousal partnership.TABLE 1: Concurrency and HIV Transmission Risk by HIV Status at MarriageSince the study did not measure the spouses' HIV status at the time of marriage, 3 of the 4 possible conditions in Table 1 confound the observed association between husbands' concurrency and wives' HIV status. The logic of the causal chain—for a couple that begins concordant negative, the husband's additional partners directly place him at risk of infection, and subsequently place his wife at risk of potential exposure—requires a longitudinal cohort study design if one wants to estimate the individual and population level contributions of concurrency to HIV transmission. With a more appropriate design, one would still want to examine other factors that will influence the impact of one spouse's concurrency on their partner's HIV exposure (eg, whether the spouses are still having sex, the partner's concurrent extraspousal partnerships, condom use, and coital frequency). The authors note the limitations of their cross-sectional study design in the conclusion, but they do not acknowledge that their study design makes it inappropriate to test these associations, and impossible to draw meaningful conclusions about the relationship between concurrency and HIV transmission within marriage.

Topic: Adolescent Sexual and Reproductive Health
Subfield: General Health Professions
Field: Health Professions
Domain: Health Sciences