Objective: To assess the impact of primary HIV infection (PHI) on the spread of HIV and the temporal trends in transmission of HIV drug resistance between 1996 and 1999 in Switzerland.
Methods: Sequencing of the genes for reverse transcriptase (RT) and protease was performed for 197 individuals with documented PHI. Phylogenetic analyses were confronted with epidemiological data.
Results: Significant clustering was demonstrated for 29% of the RT sequences. All these cases occurred closely together in place and time; contact tracing demonstrated transmission at the time of PHI in 30% of them. 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, 13% of intravenous drug users and more frequently in men (10.4%) than women (2.6%). Potential factors involved in the recent decrease of transmission of drug-resistant variants include increase of HIV non-B subtypes from 23% in 1996 to 35% in 1999 (only one non-B subtype had resistance mutations) and a steady increase of patients with undetectable viraemia as documented in Swiss HIV Cohort Study (10% in 1996 vs 53% in 1999).
Conclusions: Phylogenetic and epidemiological analyses underline the impact of PHI in the spread of HIV. Moreover, this study indicates that drug resistance transmission may have decreased recently in Switzerland through the increased frequency of infection with HIV non-B subtypes and the steady increase of patients with undetectable viraemia.
From the University Hospitals of aGeneva, bLausanne, cSt Gallen, dZurich and eBasel, fLa Source Hospital, Lausanne and the gSwiss Institute of Bioinformatics, CMU, Geneva,Switzerland, hAnnecy Hospital, France and the iCoordination and Data Centre, Swiss HIV Cohort Study, Lausanne, Switzerland. *See Appendix for members of the Swiss HIV Cohort Study.
Requests for reprints to Prof. L. Perrin, Laboratory of Virology, Geneva University Hospital, 1211 Geneva 14, Switzerland.
Received: 26 January 2001;
revised: 13 July 2001; accepted: 23 July 2001.
Sponsorship: This work was supported by the Swiss National AIDS Research Program (grant No 3100.052403.97) and the Swiss HIV Cohort Study (Swiss National Science Foundation, grant no 3345-062041).