Dynamic sex roles among men who have sex with men and transmissions from primary HIV infection

Abstract

Background: Previous studies estimating the fraction of transmissions from persons with primary HIV have not focused on the effects of switching sex role in male homosexual populations. Such behavioral fluctuations can increase the contribution of primary HIV in the overall population.

Methods: We modeled HIV transmission with 8 compartments defined by 4 behavioral groups, with different anal-insertive and anal-receptive combinations, and 2 stages of infection. We explored the effects of fluctuating behavioral categories on endemic prevalence and the fraction of transmissions from primary HIV. We varied transition rates to develop the theory on how behavioral fluctuation affects infection patterns, and we used the transition rates in a Netherlands cohort to assess overall effects in a real setting.

Results: The dynamics of change in behavior-group status over time observed in the Netherlands cohort amplifies the prevalence of infection and the fraction of transmissions from primary HIV, resulting in the highest proportions of transmissions being from people with primary HIV. Fluctuation between dual- or receptive-role periods and no-anal-sex periods mainly determines this amplification. In terms of the total transmissions, the dual-role risk group is dominant. Fluctuation between insertive and receptive roles decreases the fraction of transmissions from primary HIV, but such fluctuation is infrequently observed.

Conclusion: The fraction of transmissions from primary HIV is considerably raised by fluctuations in insertive and receptive anal sex behaviors. This increase occurs even when primary HIV or later infection status does not influence risk behavior. Thus, it is not simply biology but also behavior patterns and social contexts that determine the fraction of transmissions from primary HIV. Moreover, each primary HIV transmission has a larger population effect than each later infection transmission because the men to whom one transmits from primary HIV carry on more chains of transmissions than the men to whom one transmits later in infection. Reducing transmissions from primary HIV should be a primary focus of HIV control efforts.

FIGURE 1

Instantaneous transition rates per month for the 4 risk groups used in the deterministic compartmental model that is adapted from Blower et al.

FIGURE 2

Dynamic analysis given observed risk behavior flows from Blower et al when half of the dual-role individuals are responsible for the reciprocal sex acts. A, HIV Prevalence and fraction of transmissions from primary HIV in the overall population. B, HIV Prevalence with respect to the no-anal-sex, insertive-only, receptive-only and dual-role risk groups. C, Fraction of total transmissions from the insertive-only, receptive-only and dual-role risk groups. D, Fraction of transmission from primary HIV from the insertive-only, receptive-only and dual-role risk groups.

FIGURE 3

Equilibrium analysis given observed risk behavior flows from Blower et al. Panels (A and B) give the prevalence and fraction of transmission from primary HIV respectively for the average receptive contact rate per month for unidirectional sex for dual role contacts that are 0%, 50% and 100% reciprocal. Panels (C and D) gives the prevalence and fraction of transmission from primary HIV respectively for the average receptive contact rate per month for unidirectional sex for 80%, 67%, and 51% as the initial proportion of the population in the no anal sex group.

FIGURE 4

Equilibrium analysis under theoretical conditions to clarify causes in dynamics. Panel (A) shows the prevalence and fraction of transmission from primary HIV, varied over the dual-role population from zero to the sum of the insertive-only and receptive-only populations. Panel (B) shows the prevalence and fraction of transmission from primary HIV without persons having no anal sex for the dual-role population varied over the fluctuation rate between the insertive-only and receptive-only groups.