Using a stochastic network model based on data from four representative sub-Saharan African countries with a large HIV burden, we provide the first estimate of the epidemiologic benefits and the cost-effectiveness of changes in sexual behavior that may arise from concurrent partnership reduction campaigns. Our analysis suggests that reducing concurrent partnerships among high-risk individuals would result in the greatest reduction in new HIV infections compared to the Status Quo. However, all three of the modeled behavior change scenarios achieved relatively similar reductions in new HIV infections. In contrast to previous work which argues that concurrency reduction without targeting the most connected individuals will fail [64
], our results suggest that the message and target population matter less than the extent of partnership reduction.
Concurrent sexual partnerships increase the rate of HIV transmission by creating a connected network, and high-risk individuals are the most important links in such a network. This explains our finding that reducing the number of partnerships among the highest risk individuals has the greatest impact on HIV transmission. However, reaching the most promiscuous individuals and changing their behaviors is often difficult. Our analyses suggest that other forms of concurrency reduction provide relatively similar benefits, without the need to specifically target groups that may be hard to reach. These findings lend support to previous suggestions that reaching all members of a sexual network, not just the most promiscuous, is of great importance in preventing HIV [65
Campaigns explicitly targeting concurrent partnership reduction are relatively new and their effectiveness has yet to be measured. However, our analyses suggest that if campaigns can achieve at least modest reductions in concurrency at similar costs as other mass media campaigns, they are likely to be cost-effective and even cost saving. For example, given our baseline estimates of concurrency, our model predicts that a campaign that costs $1 per person annually need only reduce concurrent partnerships by less 5% to 15% in the study countries considered to be cost-saving, when comparing the cost per HIV infection averted to the lifetime medical costs of an HIV infection. For a campaign that is 10% effective in reducing concurrent partnerships and that costs $1 per person annually, we estimate that the cost per HIV infection averted ranges from $582 to $1,583 in the study countries considered. This places concurrency reduction on par with other established HIV prevention interventions in Africa: the costs per HIV infection averted for male circumcision in South Africa and prevention of mother-to-child transmission are $181 and $20-$2,198, respectively [61
We estimate that the maximal potential reduction in new infections due to concurrency reduction (i.e., if there are no concurrent partnerships) is about 55%, corresponding to 0.2, 2.0, 1.5, and 1.4 million infections averted in Swaziland, Tanzania, Uganda, and Zambia, respectively, over 10 years. While this is a substantial reduction in new infections, it highlights the importance of implementing complementary HIV prevention approaches. Even complete elimination of multiple concurrent sexual partnerships cannot stop HIV transmission.
Our analysis focused on the benefits of concurrency reduction for HIV prevention. However, programs that reduce concurrency may also generate additional benefits, such as reduction in the incidence of other sexually transmitted diseases. Targeting concurrent sexual partnerships may also have social benefits such as reducing intergenerational sex, a phenomenon that has likely contributed to the feminization of the HIV epidemic in Africa, and reducing domestic violence, which is commonly associated with having multiple sexual partners [11
The results presented here are contingent on the prevalence of concurrency in each of the study countries. Our estimates of concurrency behavior relied on limited data. We assumed that sexual behavior survey data on the number of sexual partners reported in the past 12 months could be used as a surrogate for the concurrency behavior in the population. This assumption may overestimate the true concurrency behavior. At the same time, sexual behavior surveys may underestimate true behavior patterns. While discussions are ongoing about how best to measure concurrency using survey methods [71
], sexual behavior surveys have yet to systematically incorporate these recommendations. In an effort to quantify the importance of this limitation on our results, we varied the prevalence of concurrency in sensitivity analysis to account for potential overestimation. We found that the rank ordering of the behavior change scenarios was unchanged, though the expected number of infections averted decreased as the prevalence of concurrency was reduced and the cost per infection averted increased. This highlights the need for better estimates of baseline sexual behavior, including the prevalence of concurrent partnerships, when considering investments in campaigns to change sexual behaviors.
Our analysis has several additional limitations. First, we assessed the relative effectiveness of different types of behavior change, but do not comment on the feasibility of such behavior changes. These considerations may vary by country. Second, our prevalence estimates depend on HIV mortality, which may change as treatment coverage changes in sub-Saharan Africa. Finally, our analysis was limited by the data informing the network structure in our model. We based the sexual partnership network structure for each of the four study countries on country-specific survey data. This data only provided us with partnership distributions, and we assumed non-preferential mixing lacking data to informing us otherwise, though populations typically do exhibit some kind of assortative mixing [72
]. Mixing patterns induced by cross-generational partnerships, in particular, could prove extremely important in the context of concurrent partnership reduction campaigns. Future work characterizing these relationships would greatly help in evaluating the impact of concurrency reduction on the course of the epidemic and could inform an extension of the current model incorporating preferential mixing patterns.
The message(s) that a concurrency reduction campaign chooses to convey have important implications. The target population may change, the cultural background may affect the message’s effectiveness, and the cost of reaching the target population may vary. Our analysis suggests that the beneficial effect of concurrency reduction is only minimally dependent on the target population and message, and greatly dependent on the achieved reduction in concurrency. Moreover, our analysis suggests that concurrency reduction campaigns can be cost-effective, or even cost-saving, under a broad range of plausible cost and effectiveness assumptions, and even if the level of concurrency is half as high as we estimated in our base case. This lends further support to the potential importance of these campaigns as a means of controlling HIV in sub-Saharan Africa.