Background: Studying HIV transmission networks provides insight into the spread of HIV and opportunities for intervention. We identified transmission dynamics among risk groups and racial/ethnic groups in the United States. Methods: For HIV-1 pol sequences reported to the US National HIV Surveillance System during 2001–2012, we calculated pairwise genetic distance, identified linked pairs of sequences (those with distance ≤1.5%), and examined transmission category and race/ethnicity of these potential transmission partners. Results: Of 40,950 sequences, 12,910 (32%) were linked to ≥1 other sequence. Of men who have sex with men (MSM) who were linked to ≥1 sequence, 88% were linked to other MSM and only 4% were linked to heterosexual women. Of heterosexual women for whom we identified potential transmission partners, 29% were linked to MSM, 21% to heterosexual men, and 12% to persons who inject drugs. Older and black MSM were more likely to be linked to heterosexual women. Assortative mixing was present for all racial/ethnic groups; 81% of blacks/African Americans linked to other blacks. Conclusions: This analysis is the first use of US surveillance data to infer an HIV transmission network. Our data suggest that HIV infections among heterosexual women predominantly originate from MSM, followed by heterosexual men. Although few MSM were linked to women, suggesting that a minority of MSM are involved in transmission with heterosexual women, these transmissions represent a substantial proportion of HIV acquisitions by heterosexual women. Interventions that reduce transmissions involving MSM are likely to also reduce HIV acquisition among other risk groups.

We evaluated several hypotheses for disparities in HIV infection between black and white MSM in the United States, including incarceration, partner HIV status, circumcision, sexual networks, and duration of infectiousness. The 2008 National HIV Behavioral Surveillance System (NHBS), a cross-sectional survey conducted in 21 US cities. MSM were interviewed and tested for HIV infection. For MSM not previously diagnosed with HIV infection, we used logistic regression to test associations between newly diagnosed HIV infection and incarceration history, partner HIV status, circumcision status, and sexual networks (older partners, concurrency, and partner risk behaviors). For HIV-infected MSM, we assessed factors related to duration of infectiousness. Among 5183 MSM not previously diagnosed with HIV infection, incarceration history, circumcision status, and sexual networks were not independently associated with HIV infection. Having HIV-infected partners [adjusted odds ratio (AOR) = 1.9, 95% confidence interval (CI) = 1.2–3.0] or partners of unknown status (AOR = 1.4, CI = 1.1–1.7) were associated with HIV infection. Of these two factors, only one was more common among black MSM – having partners of unknown HIV status. Among previously diagnosed HIV-positive MSM, black MSM were less likely to be on antiretroviral therapy (ART). Less knowledge of partner HIV status and lower ART use among black MSM may partially explain differences in HIV infection between black and white MSM. Efforts to encourage discussions about HIV status between MSM and their partners and decrease barriers to ART provision among black MSM may decrease transmission.

This report describes identification of U.S. counties as COVID-19 hotspots during March 8–July 15, 2020.

This Viewpoint describes the addition of HIV nucleotide sequence data collected through molecular surveillance to traditional epidemiologic investigation as an

CDC issued interim guidance for the prevention of sexual transmission of Zika virus on February 5, 2016. The following recommendations apply to men who have traveled to or reside in areas with active Zika virus transmission and their female or male sex partners. These recommendations replace the previously issued recommendations and are updated to include time intervals after travel to areas with active Zika virus transmission or after Zika virus infection for taking precautions to reduce the risk for sexual transmission. This guidance defines potential sexual exposure to Zika virus as any person who has had sex (i.e., vaginal intercourse, anal intercourse, or fellatio) without a condom with a man who has traveled to or resides in an area with active Zika virus transmission. This guidance will be updated as more information becomes available.