754   HIV Drug Resistance and Molecular Epidemiology in Patients with Primary HIV Infection.

S. Yerly¹, E. Race², S. Vora¹, P. Rizzardi³, J.-P. Chave³, M. Flepp⁴, P. Vernazza⁵, A. Telenti³, M. Battegay⁶, A.-L. Veuthey⁷, B. Hirschel¹, L. Perrin*¹, and the Swiss HIV Cohort Study.
¹Geneva,³Lausanne,⁴Zurich,⁵St. Gallen,⁶Basel Univ. Hosp.,⁷Swiss Inst. of Bioinformatics, CMU, Geneva, Switzerland; and²Inserm, Bichat Hosp., Paris, France.

Background:We assessed the factors associated with the transmission of HIV drug-resistant variants between 1996 and 1999 in Switzerland.

Methods:. Sequencing of reverse transcriptase and protease was performed in 197 individuals with documented primary HIV infection (PHI) and confronted with epidemiological data such as time and circumstances of the infection.

Results:Genotypic drug resistance was detected in 8.6% of PHI individuals in 1996, 14.6% in 1997, 8.8% in 1998 and 5.0% in 1999. Drug-resistant variants were identified in 11.3% of individuals infected by homosexual contacts, 6.1% by heterosexual contacts and 13% of intravenous drug users, and more frequently in men than women (10.4% vs. 2.6%), likely related to the higher frequency of HIV-1 non-B subtypes infection in females (41% vs. 21%). Potential factors involved in the decrease over years of drug-resistant variants include increase of non-B subtypes from 23% in 1996 to 35% in 1999 (only one non-B subtype had mutations associated with drug resistance) and a steady increase of patients with undetectable viremia as documented in the Swiss HIV Cohort Study (10% in 1996 vs. 53% in 1999).The impact of PHI on the spread of HIV epidemic is demonstrated by significant clustering for 29% of the sequences. All the cases occurred closely together in place and time; contact tracing demonstrated transmission at the time of PHI in 30% of them.

Conclusions:As PHI favors spreading of the epidemic, identification of these individuals is a public health priority. Treatment leading to undetectable viremia may have limited the transmission of drug-resistant variants in Switzerland.