HIV This Week

Brenner BG, Roger M, Routy JP, Moisi D, Ntemgwa M, Matte C, Baril JG, Thomas R, Rouleau D, Bruneau J, Leblanc R, Legault M, Tremblay C, Charest H, Wainberg MA; Quebec Primary HIV Infection Study Group. High rates of forward transmission events after acute/early HIV-1 infection. J Infect Dis 2007;195:951-9. Epub 2007 Feb 16.

Brenner and colleagues used a population-based phylogenetic approach to characterize human immunodeficiency virus (HIV)-transmission dynamics in Quebec. HIV-1 pol sequences included primary HIV infections (<6 months after seroconversion) from the Quebec PHI cohort (1998-2005; n=215) and the provincial genotyping programme (2001-2005; n=481). Phylogenetic analysis determined sequence interrelationships among unique primary HIV infections (n=593) and infections from untreated (n=135) and treated (n=660) chronically infected potential transmitter populations (2001-2005). Clinical features, risk factors, and drug resistance for clustered and non-clustered transmission events were ascertained. Viruses from 49.4% (293/593) of primary HIV infections co-segregated into 75 transmission chains with 2-17 transmissions/cluster. Half of the clusters included 2.7+/-0.8 (mean+/-SD) transmissions, whereas the remainder had 8.8+/-3.5 transmissions. Maximum periods for onward transmission in clusters were 15.2+/-9.5 months. Co-clustering of untreated and treated chronically infected individuals with primary HIV infections were infrequent (6.2% and 4.8%, respectively). The ages, viremia, and risk factors were similar for clustered and non-clustered transmission events. Low prevalence of drug resistance in primary HIV infections supported amplified transmissions at early stages. The authors conclude that early infection accounts for approximately half of onward transmissions in this urban North American study. Therapy at early stages of disease may prevent onward HIV transmission.

Editors’ note : This phylogenetic study confirms what has been predicted from mathematical modelling: a substantial proportion of HIV transmission occurs during primary infection when many people may be unaware that they have HIV infection. Beyond emphasising the importance of intensifying prevention efforts to reduce the number of primary infections, these results could have implications for post-exposure prophylaxis for those who may have been exposed and suppressive treatment for those in the first 6 months of infection.