Analysis of HIV nucleotide sequence data collected through the National HIV Surveillance System can identify rapidly growing transmission clusters. The Centers for Disease Control and Prevention (CDC) identified a molecular cluster in Texas that grew substantially during July 2015–June 2016. CDC and the Texas Department of State Health Services investigated to define the extent of the cluster, identify relationships between cases, characterize the epidemiology and factors facilitating transmission, characterize timing of viral suppression, and prioritize intervention.
Persons in the molecular cluster were considered confirmed cluster cases. Based on partner services interview records, we identified HIV-infected persons without nucleotide sequences available for analysis who were named sex or needle sharing partners of confirmed cases, partners of sex or needle sharing partners, or social network contacts of confirmed cases. During August–October 2016, we reviewed medical records and partner services interview records to collect data on demographics, risk behaviors, partner meeting sites, and time to achieve viral suppression.
From 27 confirmed cluster cases, we identified 112 additional cluster cases. Of 27 confirmed cases, 12 (44%) were connected through named partners or social contacts into one large cluster; no links were identified for 15. Of 76 confirmed and other cluster cases with records available, 76 (100%) were male at birth, 59 (78%) were aged 13–29 y, 66 (87%) were Hispanic, and 68 (89%) reported sex with men. Reported lifetime sex partners ranged from 2–300; 18 (24%) reported anonymous partners and 18 (13%) had an STD diagnosis within 12 months before HIV; none were on PrEP. In all, 31 (41%) had evidence of viral suppression within 6 months of diagnosis (figure); 10 (13%) have never had a viral load test. After this investigation, 25 people were initiated for reengagement in care.
Our investigation identified an actively growing transmission cluster of primarily young Hispanic MSM that was substantially larger than the molecular cluster; this network is likely even larger, given the large number with anonymous partners or without identified links to the cluster. High risk sexual behavior coupled with delays in achieving viral suppression among some cluster cases likely contributed to rapid growth. These findings reveal opportunities for prioritization of persons associated with this cluster for linkage to care and PrEP referral.