15th Annual Conference of the British HIV Association 1-3 April 2009, Liverpool, UK

HIV TRANSMISSION AMONGST MSM: ASSOCIATION WITH ANTIRETROVIRAL THERAPY, INFECTION STAGE, VIRAEMIA AND SEXUALLY TRANSMITTED INFECTIONS (STI) IN A LONGITUDINAL PHYLOGENETIC STUDY

HIV Med 2009 Apr 1-3 (Suppl 1);15:10 (abstract no. O18)

M Fisher¹, K Nambiar¹, A Brown², S Sudarshi¹, D Pao¹, N Gill², C Sabin³ and D Pillay^2
1Brighton and Sussex University Hospitals NHS Trust, Brighton, UK, ²Health Protection Agency, Colindale, UK, ³Royal Free and University College Medical School, London, UK

BACKGROUND: HIV transmission continues among men who have sex with men (MSM). Previous transmission studies have been limited by various methodological imprecisions, in particular an inability to account for infection stage changes over time. Using a phylogenetic, clinical and epidemiological approach, we identify key determinants of the epidemic.

METHODS: Potential subjects were MSM from a geographically contained population between 2000 and 2006. Individuals were classified such that they could move from acute to chronic infection categories. Pol sequences were obtained from plasma virus or proviral DNA (where viral load was <1000 c/mL) and clusters estimated by maximum likelihood methods as well as conservative genetic distance differences. RI was defined by a previous HIV-1 Ab result within 6 months, STARHS (if subtype B), p24 Ag+/Ab-status, or limited western blot. The single most likely transmitter generating each RI was identified within clusters, and risk factors around the time of the likely transmission identified using a multivariable poisson regression model.

RESULTS: Of 1144 MSM, pol sequence data was obtained for 859 (75%), of which 159/859 (10%) were RI. A single most likely transmitter was identified for 41/159 (26%); 10/41 (24%) were RI. Factors associated with transmission by multivariable analysis were: younger age (rate ratio per 5 years older 0.69 [95% CI 0.55–0.87]; P=0.002); higher VL (RR per log higher 1.61 [1.14–2.27]; P=0.007); RI (RR 3.25 [1.44–7.31]; P=0.005); and recent STD (RR 5.99 [2.81–12.74]; P=0.0001). Use of HAART appears to significantly reduce transmission in the univariable model, RR 0.04 (0.01–0.19; P=0.0001).

CONCLUSIONS: Onward transmission of HIV amongst MSM is associated with RI, STI and higher VL, and is reduced by HAART. The majority of new infections, however, appear to occur from individuals whose infection is undiagnosed. Strategies to control the epidemic amongst MSM must consider earlier diagnosis, increased HIV testing, improved STI control, and use of HAART to reduce infectivity.

2009-04-01
O18

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