Circulation of HIV-1 subtype A within the subtype C HIV-1 epidemic in Tamil Nadu, India

The HIV‐1 epidemic in India is caused mainly by subtype C viruses that are transmitted sexually and by injecting drug use. The state of Tamil Nadu in Southern India has an HIV‐1 median prevalence of 16.8% among injecting drug users, 6.6% in men who have sex with men, and 4.6% in female sex workers. In the rural district of Namakkal, a prevalence >3% was detected among antenatal women. The goal of this study was to determine the HIV‐1 molecular epidemiology in Tamil Nadu. Blood samples were collected from 40 high‐risk HIV‐seropositive individuals from Chennai and Namakkal. HIV‐1 subtype was determined by envelope nucleotide sequencing. Among the samples studied, 85% were subtype C, however, a cluster of subtype A samples (12.5%) and one subtype E recombinant form CRF01_AE (close to the Thailand strains) were detected. The average genetic distance of subtype C samples from Chennai and Namakkal were 9.44 ± 0.77% and 11.8 ± 0.7%, respectively indicating an evolved epidemic. This pilot study confirmed that subtype C was predominant in these regions but an outbreak of subtype A was detected in Namakkal. These results stress the importance of periodic monitoring of circulating HIV‐1 subtypes in South India. J. Med. Virol. 84:1507–1513, 2012. © 2012 Wiley Periodicals, Inc.