Per-contact probability of HIV transmission in homosexual men in Sydney in the era of HAART.
OBJECTIVE
The objective of this study is to estimate per-contact probability of HIV transmission in homosexual men due to unprotected anal intercourse (UAI) in the era of HAART.


METHODS
Data were collected from a longitudinal cohort study of community-based HIV-negative homosexual men in Sydney, Australia.


METHODS
A total of 1427 participants were recruited from June 2001 to December 2004. They were followed up with 6-monthly detailed behavioral interviews and annual testing for HIV till June 2007. Data were used in a bootstrapping method, coupled with a statistical analysis that optimized a likelihood function for estimating the per-exposure risks of HIV transmission due to various forms of UAI.


RESULTS
During the study, 53 HIV seroconversion cases were identified. The estimated per-contact probability of HIV transmission for receptive UAI was 1.43% [95% confidence interval (CI) 0.48-2.85] if ejaculation occurred inside the rectum, and it was 0.65% (95% CI 0.15-1.53) if withdrawal prior to ejaculation was involved. The estimated transmission rate for insertive UAI in participants who were circumcised was 0.11% (95% CI 0.02-0.24), and it was 0.62% (95% CI 0.07-1.68) in uncircumcised men. Thus, receptive UAI with ejaculation was found to be approximately twice as risky as receptive UAI with withdrawal or insertive UAI for uncircumcised men and over 10 times as risky as insertive UAI for circumcised men.


CONCLUSIONS
Despite the fact that a high proportion of HIV-infected men are on antiretroviral treatment and have undetectable viral load, the per-contact probability of HIV transmission due to UAI is similar to estimates reported from developed country settings in the pre-HAART era.
National Centre in HIV Epidemiology and Clinical Research, University of New South Wales, Darlinghurst, Australia. jjin@nchecr.unsw.edu.au
Fengyi
F
Jin
James
J
Jansson
Matthew
M
Law
Garrett P
GP
Prestage
Iryna
I
Zablotska
John C G
JC
Imrie
Susan C
SC
Kippax
John M
JM
Kaldor
Andrew E
AE
Grulich
David P
DP
Wilson
D000293:Adolescent; D000328:Adult; D000368:Aged; D023241:Antiretroviral Therapy, Highly Active; D001315:Australia / Q000453:epidemiology; D015658:HIV Infections / Q000453:epidemiology / Q000523:psychology* / Q000635:transmission; D007722:Health Knowledge, Attitudes, Practice; D006716:Homosexuality / Q000523:psychology; D006801:Humans; D008297:Male; D008875:Middle Aged; D011336:Probability; D012309:Risk-Taking; D012725:Sexual Behavior / Q000523:psychology*; D012747:Sexual Partners / Q000523:psychology*; D019562:Viral Load; D055815:Young Adult