RESUMEN
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.