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BOSTON -- The rate of HIV infections in "rapidly growing" transmission clusters was 11 times the estimated U.S. national average, according to a presented at the (CROI) in Boston.

HIV transmission in these clusters occurred at a median of 44 transmission events (ranging from 21 to 132 events) per 100 person-years compared with the national average of four transmission events per 100 person-years, reported Anne Marie France, PhD, of the CDC.

Not surprisingly, these rapidly growing clusters had significantly higher portions of young men who have sex with men (MSM), as well as young Hispanic or Latino MSM.

At a press conference, France said that traditional HIV surveillance data have limitations that can't pinpoint the leading edge of HIV transmission. To combat this problem, researchers used molecular phylogeny, which can be used to analyze the hereditary molecular differences in DNA sequences. This technique would "enable state and local health departments to identify where HIV transmission is occurring," said France.

"Identification of these clusters offers the possibility of very early treatment of HIV infection, which is critical to personal health and should serve to 'bust the cluster,'" Myron Cohen, MD, of the University of North Carolina at Chapel Hill, who was not involved with the research, told MedPage Today. "Such use of new and evolving technical advances greatly increases the efficiency of public health interventions directed at HIV."

The CDC analyzed molecular sequence data reported to the at quarterly intervals from December 2015 to December 2016. France and colleagues examined this data on diagnosed HIV infections within the prior 3 years. They discovered similar strains of virus by calculating the genetic distance between sequences with only half a percent of variation between them. "Rapidly growing clusters" were defined as those with at least five diagnoses during the most recent 12-month period.

There were 51,750 persons with HIV sequences analyzed, and of those, 60 rapidly growing transmission clusters were identified. Rapidly growing clusters ranged from 5 to 42 persons, were identified in all regions of the country and involved 20 states.

Of the 903 persons in these rapidly growing clusters, a significantly higher portion were young MSM compared with the 50,847 persons not in these clusters (61% versus 32%, respectively, P<0.0001) and young Hispanic/Latino MSM (26% versus 10%, respectively, P<0.0001).

"When an HIV priority cluster is detected, public health experts can follow up locally and find out what additional prevention services are needed in the area," said France.

She said that this data held "tremendous promise in identifying networks of potential concern."

Multiple factors may be contributing to these elevated transmission rates, France noted at the press conference. For example, a disproportionate number of people in the cluster may not have viral suppression, so they may need linkage to care activities. There also may be a higher number of individuals who have yet to be diagnosed or are not aware of their HIV status, which would provide "opportunities for testing so they can get on antiretroviral therapy."

Wafaa El-Sadr, MD, of Columbia University Mailman School of Public Health in New York City, who moderated the session, but was not involved with the research, characterized these efforts as "precision prevention, by really knowing where the transmission is happening."

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