Top 5 Takeaways

  1. Prevalence and Demographics: The majority of large HIV molecular clusters with rapid transmission are primarily among gay, bisexual, and other men who have sex with men (MSM), with clusters found in all geographic regions of the U.S.
  2. Cluster Characteristics: These clusters exhibit rapid growth, varying demographic characteristics, and significantly higher transmission rates compared to national estimates.
  3. Impact of HIV Clusters: The presence of these clusters highlights the urgent need for targeted interventions to improve access to HIV prevention and treatment services, especially for MSM.
  4. Diversity within Clusters: Clusters consist of diverse populations in terms of age, race, ethnicity, and transmission categories, necessitating tailored public health responses.
  5. Public Health Strategy: Effective response requires swift action, understanding of affected communities, and implementation of focused interventions to reduce HIV transmission among MSM.


Original Article Author and Citation

Corresponding Author

Stephen M. Perez,

Suggested Citation

Perez SM, Panneer N, France AM, et al. Clusters of Rapid HIV Transmission Among Gay, Bisexual, and Other Men Who Have Sex with Men — United States, 2018–2021. MMWR Morb Mortal Wkly Rep 2022;71:1201–1206. DOI: .


This article focuses on the characterization of large HIV molecular clusters detected through the analysis of HIV-1 nucleotide sequence data from the National HIV Surveillance System. Among 38 clusters first detected during 2018–2019 and having more than 25 persons by December 2021, 29 predominantly involved MSM. These clusters were diverse in terms of demographics and exhibited a median growth rate of nine persons per year.


The study involved analysis of HIV-1 polymerase sequences, derived from routine HIV drug resistance testing, to detect molecular clusters indicative of rapid transmission. Clusters were defined based on nucleotide substitutions per site and the number of diagnoses in a given period. The primary transmission categories were assessed for each cluster.


The analysis revealed the predominance of MSM in large HIV clusters, highlighting significant disparities in HIV transmission. The variation in demographics across clusters underscores the complexity and diversity of affected communities. This diversity necessitates a more nuanced and targeted approach to public health interventions.


The findings stress the importance of rapid, tailored response interventions for HIV clusters primarily among MSM. It underscores the need for comprehensive strategies encompassing HIV testing, prevention, and treatment. Public health responses should be adaptive to the unique needs of diverse MSM populations to effectively curb HIV transmission.



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