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CSU 50/2009: HETEROSEXUAL RISK OF HIV-1 INFECTION PER SEXUAL ACT
Writing in The Lancet Infectious Diseases, Boilly and her colleagues review
the evidence, from developed and developing countries, on the risk of HIV
acquisition per heterosexual act. Although the risk of HIV acquisition is
generally less than 1 percent per act, receptive anal intercourse was
associated with higher risk; so was intact foreskin in the male; so were
the early and the late stages of HIV infection in the seropositive
partner.
Abstract of their article is below; full text is at
http://www.thelancet.com/journals/laninf/article/PIIS1473-3099
(09)70021-0/fulltext
Their review confirms the earlier work of Powers and colleagues, available
on the Internet at
http://www.thelancet.com/journals/laninf/article/PIIS1473-3099
(08)70156-7/fulltext
In their summary, Powers and colleagues express reservations about the use
of the often cited value of 0.001.
‘Studies of cumulative HIV incidence suggest that cofactors such as genital
ulcer disease, HIV disease stage, and male circumcision influence HIV
transmission; however, the heterosexual infectivity of HIV-1 is commonly
cited as a fixed value (approximately 0·001, or one transmission per 1000
contacts). . . . Infectivity estimates were very heterogeneous, ranging
from zero transmissions after more than 100 penile-vaginal contacts in some
serodiscordant couples to one transmission for every 3·1 episodes of
heterosexual anal intercourse. . . . A single value for the heterosexual
infectivity of HIV-1 fails to reflect the variation associated with
important cofactors. The commonly cited value of 0·001 was estimated among
stable couples with low prevalences of high-risk cofactors, and represents
a lower bound. Cofactor effects are important to include in epidemic
models, policy considerations, and prevention messages.’
Good reading.
Bob Davis
Review
The Lancet Infectious Diseases, Volume 9, Issue 2, Pages 118 - 129,
February 2009
doi:10.1016/S1473-3099(09)70021-0
Heterosexual risk of HIV-1 infection per sexual act: systematic review and
meta-analysis of observational studies
Original Text
Dr Marie-Claude Boily PhD a c d , Rebecca F Baggaley PhD a, Lei Wang PhD e,
Benoit Masse PhD e, Richard G White PhD b, Prof Richard J Hayes DSc b, Prof
Michel Alary PhD c d
Summary
We did a systematic review and meta-analysis of observational studies of
the risk of HIV-1 transmission per heterosexual contact. 43 publications
comprising 25 different study populations were identified. Pooled
female-to-male (0·04% per act [95% CI 0·01—0·14]) and male-to-female (0·08%
per act [95% CI 0·06—0·11]) transmission estimates in high-income countries
indicated a low risk of infection in the absence of antiretrovirals.
Low-income country female-to-male (0·38% per act [95% CI 0·13—1·10]) and
male-to-female (0·30% per act [95% CI 0·14—0·63]) estimates in the absence
of commercial sex exposure (CSE) were higher. In meta-regression analysis,
the infectivity across estimates in the absence of CSE was significantly
associated with sex, setting, the interaction between setting and sex, and
antenatal HIV prevalence. The pooled receptive anal intercourse estimate
was much higher (1·7% per act [95% CI 0·3—8·9]). Estimates for the early
and late phases of HIV infection were 9·2 (95% CI 4·5—18·8) and 7·3 (95% CI
4·5—11·9) times larger, respectively, than for the asymptomatic phase.
After adjusting for CSE, presence or history of genital ulcers in either
couple member increased per-act infectivity 5·3 (95% CI 1·4—19·5) times
versus no sexually transmitted infection. Study estimates among
non-circumcised men were at least twice those among circumcised men.
Low-income country estimates were more heterogeneous than high-income
country estimates, which indicates poorer study quality, greater
heterogeneity of risk factors, or under-reporting of high-risk behaviour.
Efforts are needed to better understand these differences and to quantify
infectivity in low-income countries.
a Department of Infectious Disease Epidemiology, Faculty of Medicine,
Imperial College, London, UK
b Department of Epidemiology and Population Health, London School of
Hygiene and Tropical Medicine, London, UK
c Population Health Research Unit, Hôpital du Saint-Sacrement, Centre
Hospitalier, University of Quebec, Quebec City, Quebec, Canada
d Department of Social and Preventive Medicine, Faculty of Medicine, Laval
University, Quebec City, Quebec, Canada
e Statistical Center for HIV/AIDS Research and Prevention, Fred Hutchinson
Cancer Research Center, Seattle, WA, USA
Correspondence to: Dr Marie-Claude Boily, Department of Infectious Disease
Epidemiology, Imperial College, Norfolk Place, London N1 3LG, UK