Background:  Since the first start of zidovudine (ZDV) in Thailand around 1988 followed by the large-scale use of HAART as first-line therapy in 2001 with fixed-dose combination of stavudine (d4T)/lamivudine (3TC)/nevirapine (NVP), HIV drug resistance has been increasingly observed, particularly when viral load and resistance testing are not available in Thailand. At the same time, prevention effort has been weakening as evidenced by the recent increase of sexually transmitted diseases in the general population and the pregnancy rate among infected individuals. This prompts the first study of HIV drug resistance transmission in Thailand.

Methods:   We subjected to in-house genotypic drug-resistance assay, 50 consecutive plasma samples each from recently seroconverted (within the last 12 months) returned blood donors of the Thai Red Cross (TRC) National Blood Centre and from recently infected (BED assay positive) clients of the TRC voluntary counseling and testing (VCT) center, all in Bangkok Metropolitan Area (BMA) during July 2005 to April 2006. HIV reverse transcriptase (RT) and protease (Pr) genes (780 bp for RT, codon 20-260, and 392 bp for Pr, codon 1-99) were reverse transcribed and then subjected to nested polymerase chain reaction (PCR) and sequenced.

Results:  We obtained 50 consecutive seroconverted returned blood donors from a total population of  440,000 donors during the study period, of whom 76% were male and the mean age was 31.3 years (8.1). The mean number of blood donations (including the last donation) was 12.8 (2 to 77) with mean interval of their earlier HIV^– donations of 6.4 (3 to 12) months. The 50 consecutive BED⁺ VCT individuals were obtained from 342 anti-HIV⁺ individuals of the VCT center, which has the HIV prevalence of 16.54 %. Of interest is that among 36 BED⁺ males were predominantly homosexual or bisexuals (23 of 36, 63.9%) as compared to 32.3% (60 of 186 BED^– males) (p <0.05), which corresponds to the recent finding of increased HIV transmission among Thai male homosexuals. We amplifiable and sequenced 46 samples from blood donors and 35 samples from VCT clients. No major resistance-associated mutations were found in any of the specimens. The results indicate a low prevalence (<5%) of HIV drug resistance transmission.

Conclusions:  Although ART has been instituted for almost 2 decades in Thailand, the transmission of HIV drug resistance remains low. Longitudinal survey of a more diverse group of populations in Thailand is needed, as well as measures to prevent HIV drug resistance in treated patients and to enhance primary and secondary HIV prevention.