Background The velocity of STI spread depends in part on the formation of sexual partnerships and the structure of sexual networks. Dual outbreaks of HIV and syphilis have persisted in NC since 2001 among young black men who have sex with men (MSM). During 2007–2009, the incidence rate of early stage syphilis increased 600% in County X from 9/100 000 to 57/100 000; the outbreak involved MSM, bisexual men (MSMW), heterosexual men (MSW), and women. We sought to determine if bisexual men bridged MSMs and heterosexuals to facilitate syphilis and HIV spread in both populations.
Methods We abstracted public health department charts in County “X” for early stage syphilis cases and HIV for black men ages 15–30 during 2006–2009. We documented each sexual and social tie, permitting sociometric analysis.
Results Of the 532 cases with syphilis, HIV, or both infections, 69% were male. The per cent of males declined with age from 24% to 18% to 13% for ages 21–25, 26–30, and 31–35 respectively, whereas women in each age group were equally distributed between 16% and 18%. Women, MSW, and MSM, accounted for 31%, 32% and 30% respectively of cases; 7% were bisexual men. Though most heterosexuals had only syphilis, 16% were HIV+ and 38% of them were coinfected. Among 196 bisexual and MSM, 73% were HIV+; of these, half were coinfected. On the basis of timing of HIV and syphilis diagnoses and syphilis stage, an estimated 33% of HIV+ men may have serosorted. Unlike other MSM populations, these cases did not use methamphetamine; 35% reported marijuana use. Crack cocaine use was reported for 16% of MSW and 33% of women. A total of 2099 individuals (cases, uninfected contacts, and anonymous partners) made up the network divided into 293 components. The largest component of 261 people (Abstract P1-S5.39 figure 1) was predominantly MSM including 10 of the 36 MSMW. None of MSMWs' female partners had other partners, suggesting that onward transmission did not occur. Heterosexuals, engaging in transactional sex, comprised the second largest component involving at least 135 individuals; all cases were syphilis-infected.
Conclusions Contemporaneous syphilis and HIV epidemics persist among MSM; neither serosorting nor methamphetamine use fuels spread. Heterosexuals experienced a syphilis outbreak driven in part by transactional sex and crack cocaine use. Bisexual men did not bridge the populations. Frequent dual screening among MSM is critical to impede further transmission of both STIs.
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