AEGiS-14IAC: Determination of the minimum incidence of HIV-1 dual subtype infections among injection drug users (IDUs) in Bangkok, Thailand.

14th International AIDS Conference

Barcelona, Spain - July 7-12, 2002

Determination of the minimum incidence of HIV-1 dual subtype infections among injection drug users (IDUs) in Bangkok, Thailand.

Int Conf AIDS 2002 Jul 7-12; 14:(abstract no. TuOrC1194)

Hu DJ, Subbarao S, Vanichseni S, Mock PA, Ramos A, Nguyen L, Choopanya K, Mastro TD
Centers for Disease Control and Prevention, Atlanta, United States

BACKGROUND: Although dual infections involving different subtypes of HIV-1 have been reported, unbiased estimates of their frequency from longitudinal studies have not previously been determined.

METHODS: To determine the proportion and incidence of infections with subtype B and CRF01_AE (E) among IDUs in Bangkok, 1209 HIV-negative IDUs were followed in a prospective cohort study. After 2308 person-years of follow-up, 133 seroconverted to HIV-1 (20% were subtype B and 80% E). Specimens from 78 individuals were available at their first positive (FP) and more than 12 months later (T12). The presence of mixed infections was identified by a combination of restriction fragment length polymorphism and phylogenetic analyses of cloned protease coupled with subtype-specific amplification of envelope gp120.

RESULTS: Two cases of dual B/E infection (2.6%) were found among the 78 seroconverters. The minimum observed one-year incidence of dual B/E infection among initially uninfected but at-risk IDU was calculated to be 2/78 x 133/2308 = .0015, compared to an estimated exposure to both subtypes of .0005 or the product of subtype-specific annual incidences for B - 0.012 and E- 0.043.

CONCLUSIONS: This is the first determination of the incidence of dual subtype infection and as a minimum estimate, confirms that coinfection is not rare in a population with high incidence with more than one circulating subtype. As Thailand is also the site of the world's first efficacy trial of a bivalent HIV-1 subtype vaccine, our findings pose important questions not only on the mechanisms of immune protection but raise challenges for vaccine development and other prevention interventions.

Keywords: AEGIS, Incidence, HIV Infections, HIV-1, Thailand, Cohort Studies, Longitudinal Studies, Prospective Studies, epidemiology

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