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Determinants of HIV-1 transmission in men who have sex with men: a combined clinical, epidemiological and phylogenetic approach

Fisher, Martina; Pao, Davida; Brown, Alison Eb,c; Sudarshi, Darshana; Gill, O Noelb; Cane, Patriciab; Buckton, Andrew Jb; Parry, John Vb; Johnson, Anne Mc; Sabin, Carolinec; Pillay, Deenanb,d

doi: 10.1097/QAD.0b013e32833ac9e6
Epidemiology and Social

Objectives: To identify biological factors associated with HIV transmission in men who have sex with men (MSM).

Design: A longitudinal phylogenetic analysis of HIV-1 from an MSM cohort, incorporating clinical and epidemiological data.

Methods: Potential individuals were HIV-infected MSM attending a sexual health clinic between 2000 and 2006. Individuals were classified such that they could move from recent to chronic infection categories. HIV-1 pol gene sequences were obtained from plasma virus or proviral DNA and clusters estimated by maximum likelihood and conservative genetic distance differences. The single most likely transmitter generating each recent infection was ascertained and risk factors around time of likely transmission explored using Poisson regression modelling.

Results: Out of 1144 HIV-infected MSM, pol sequence data were obtained for 859 (75%); 159 out of 859 (19%) were recently HIV infected at diagnosis. A single most likely transmitter was identified for 41 out of 159 (26%), of which 11 were recently infected (27%) and 30 chronically infected. Factors associated with transmission in multivariable analysis were: younger age {rate ratio per 5 years older 0.68 [95% confidence interval (CI) 0.54–0.86], P = 0.0009}, higher viral load [rate ratio per log higher 1.61 (95% CI 1.15–2.25), P = 0.005], recent infection [rate ratio 3.88 (95% CI 1.76–8.55), P = 0.0008] and recent sexually transmitted disease [rate ratio 5.32 (95% CI 2.51–11.29), P = 0.0001]. HAART was highly protective in a univariable model, RR 0.14 (95% CI 0.07–0.27, P = 0.0001).

Conclusion: Onward transmission of HIV among MSM is significantly associated with recent infection, sexually transmitted diseases and higher viral load, and reduced by effective HAART. The majority of new infections appear to occur from individuals whose infection was undiagnosed at the time of transmission.

aHIV/GUM Research Department, Brighton and Sussex University Hospitals NHS Trust, Brighton, UK

bCentre for Infections, Health Protection Agency, UK

cResearch Department of Infection and Population Health, University College London, UK

dUCL/MRC Centre for Medical Molecular Virology, Division of Infection and Immunity, University College London, London, UK.

Received 27 November, 2009

Revised 17 February, 2010

Accepted 22 March, 2010

Correspondence to Dr Martin Fisher, HIV Research Department, Brighton and Sussex University Hospitals NHS Trust, Sussex House, Abbey Road, Brighton BN2 5BE, UK. E-mail:

© 2010 Lippincott Williams & Wilkins, Inc.