More than a third of the sample reported injecting exclusively with HIV-positive partners, and about 60% of them reported engaging in injection risk behavior with these partners. These numbers are comparable to the numbers found in the analysis of sexual serosorting, and suggest that some of HIV-positive IDUs do limit risky injection practices to seroconcordant partners. Very few (<10%) reported injecting exclusively with HIV-negative partners. However, unlike the finding on sexual serosorting, injection risk among this group was not necessarily the lowest; about 60% reported engaging in injection risk behavior with their HIV-negative partners.
Almost half of the sample had injection partners of unknown HIV status and more than 10% had HIV-positive and HIV-negative partners but no partners of unknown HIV status. Injection risk, including the number of injection partners, was higher among the groups with partners of mixed HIV status than groups that had either exclusively HIV-positive or exclusively HIV-negative injection partners. These groups also reported higher frequencies of injection, using greater numbers of different substances, and were also more likely to inject stimulants such as cocaine or crack and “speedball” than the group that had exclusively HIV-positive injection partners or the group that had exclusively HIV-negative injection partners. Despite these differences in risk behaviors, the four groups were not significantly different from each other with respect to socio-demographic and psychosocial factors.
At first glance, the finding that the group with any unknown status injection partners (group U) was riskier than groups that had either exclusively HIV-positive (group P) or exclusively HIV-negative injection partners (group N) appeared to be consistent with the previous finding on sexual partner sorting.16
The finding could mean that not knowing the HIV status of all injection partners is related to risky injection behavior. However, an alternative explanation is that the greater number of injection partners reported in group U may be simultaneously associated with not knowing the HIV status of all of their injection partners and also with greater risky injection behavior, and the number of injection partners may in fact be the factor driving risk behavior. Indeed, when the number of injection partners was controlled for in a model examining the differences between group U and other groups, the group differences in risky injection behavior (between groups U and P and also between groups U and N) became no longer significant. Moreover, the number of injection partners was a significant predictor of risky injection behavior. It is noteworthy that controlling for factors such as number of injections and injection of cocaine/crack or speedball did not fully eliminate the group differences although injection of cocaine/crack and speedball did eliminate the difference between groups U and N. It appears that unlike in the context of sexual risk taking, participants in group U may be more likely to engage in risky injection behavior not because they do not know all of their partners’ HIV status but because they have more injection partners (and thus have more opportunity to engage in risk behavior).
The findings that the group with HIV-positive and HIV-negative injection partners, but no partners of unknown HIV status (group M), is equally risky as group U and also is riskier than groups P and N suggests that once again, having knowledge of all injection partners may not lead to safer injection behavior. Moreover, in contrast to the difference between group U and other groups mentioned above, the differences between group M and groups P and N were not explained by any of the factors including number of injection partners. The finding suggests that some untested factors may drive the risk behavior of those with injection partners of known mixed HIV status. More data are needed to fully understand this group and to provide explanations for why having injection partners of known mixed HIV status should be associated with risk.
This study has the following limitations. First, the data are cross-sectional, thus, no causal relationships can be established between partner selection and risk behavior. Second, the data were drawn from a convenience sample of HIV-positive IDUs enrolled in an intervention trial, and thus the findings cannot be generalized to a broader population of HIV-positive IDUs. Third, although choosing injecting partners of a particular HIV status may be intentional (e.g., choosing to inject only with HIV-positive partners), in reality, some participants may have met injection partners who happened to be of particular HIV status. Although we assessed partner’s HIV status from the questions asking how many of their partners told them that they were HIV-positive or HIV-negative, etc., the accuracy of partner’s HIV status (whether the participants accurately recalled what their partners had told them or whether the partners had accurate knowledge of their HIV status) is uncertain. The issue of accurate recall of partner’s HIV status may be an issue particularly when a person has many injection partners. Lastly, our study measures did not include the serostatus for hepatitis C, which is readily transmitted by risky injection practices and prevalent among IDUs.17,29
It should be noted that serosorting by HIV status does not preclude HCV infection and implications of HIV serosorting on HCV infection should be further considered.
Despite these limitations, this study broadens the scope of earlier work on serosorting of sexual partners among HIV-positive IDUs. Our analysis suggests that injection serosorting (i.e., limiting risky injection behavior to seroconcordant partners) appeared to be occurring among some, but not an overwhelming majority of HIV-positive IDUs. We also found that HIV-positive IDUs who do not limit injection partners to persons of a particular HIV status were more likely than those who adopt such a partner sorting strategy to engage in risky injection or substance-use behaviors. However, we also found that having knowledge of HIV status of all injection partners per se did not appear to be as important as having knowledge of all sexual partners’ HIV status in its association with risk behavior. These findings suggest that interventions targeting HIV-positive IDUs may need to focus on those who do not utilize any partner sorting strategies and to identify and address the underlying factors that may be driving their risk behaviors (e.g., greater number of injection partners), rather than focusing on knowing the HIV status of all injection partners. To our knowledge, this study is one of the first to explore HIV status-based selection of injection partners and to examine its association with risk behaviors. This study represents a beginning to understanding potential processes of serosorting and other partner-selection strategies of IDUs. With more sophisticated measures of serosorting, future research should be able to more clearly identify the patterns of sexual and injection partner selection among HIV-positive IDUs. Such information may further inform the development of novel preventive intervention strategies for the population.