title: Determinants of HIV-1 transmission in men who have sex with men: a combined clinical, epidemiological and phylogenetic approach.
abstract: OBJECTIVE
  To identify biological factors associated with HIV transmission in men who have sex with men (MSM).
  
  
  METHODS
  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-1pol 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).
  
  
  CONCLUSIONS
  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.
authors.affiliation: HIV/GUM Research Department, Brighton and Sussex University Hospitals NHS Trust, Brighton, UK. martin.fisher@bsuh.nhs.uk
authors.forename: Martin
authors.initials: M
authors.lastname: Fisher
authors.forename: David
authors.initials: D
authors.lastname: Pao
authors.forename: Alison E
authors.initials: AE
authors.lastname: Brown
authors.forename: Darshan
authors.initials: D
authors.lastname: Sudarshi
authors.forename: O Noel
authors.initials: ON
authors.lastname: Gill
authors.forename: Patricia
authors.initials: P
authors.lastname: Cane
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Buckton
authors.forename: John V
authors.initials: JV
authors.lastname: Parry
authors.forename: Anne M
authors.initials: AM
authors.lastname: Johnson
authors.forename: Caroline
authors.initials: C
authors.lastname: Sabin
authors.forename: Deenan
authors.initials: D
authors.lastname: Pillay
mesh_terms: D000328:Adult; D023241:Antiretroviral Therapy, Highly Active; D018791:CD4 Lymphocyte Count; D004739:England / Q000453:epidemiology; D015658:HIV Infections / Q000453:epidemiology / Q000276:immunology / Q000635:transmission* / Q000821:virology; D015497:HIV-1 / Q000235:genetics*; D018451:Homosexuality, Male; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D010802:Phylogeny; D012749:Sexually Transmitted Diseases / Q000453:epidemiology; D019562:Viral Load