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Background:  Data from new HIV-1 infections in San Francisco showed that transmission of drug-resistant HIV has increased over time up to 25% in 2002. We studied new HIV-1 infections in Amsterdam during the period 1994 to 2002. New infections were identified at the Academic Medical Centre (AMC) and within the Amsterdam Cohort Studies (ACS) on HIV and AIDS among homosexual men and drug users.

Methods:  Newly infected HIV⁺ patients identified at the AMC by evolving serology, often have symptoms of acute retroviral syndrome. Participants within the ACS seroconvert during follow-up, which makes it possible to include new non-virulent infections in our study. Additional new infections were identified among participants entering the ACS unaware of their HIV-positive status, using a less sensitive enzyme immunoassay (LS-EIA). Sequences of reverse transcriptase (RT) and protease were obtained by population-based nucleotide sequence analysis of the HIV pol gene at the first HIV RNA sample available. Mutations were identified based on the IAS-USA resistance table. HIV-1 subtypes were determined by phylogenetic analyses of RT-sequences.

Results:  Of the 100 new HIV-1 infections we identified, 32 at AMC were primary infections; in the ACS, 5 were identified by LS-EIA and 63 seroconversions. Only 1 of the ACS participants and 5 of the AMC patients were infected with non-B subtypes. The latter were Dutch heterosexuals, 4 of whom reported having a foreign partner. Transmission of HIV resistance to any ART was found in 13 of 100 new infections (13%). There were 2 cases of transmission with strains bearing mutations associated with resistance to nNRTI (2/100; 2%), and 1 case of transmission with a strain resistant to PI (1/100;1%). The other 10 carried resistant mutations against NRTI (10/100; 10%). There were no multidrug-resistant strains. During the first 4 years of our study 10 of 48 (21%) infections carried drug-resistant mutations. In the last 5 years of our study the transmission of drug resistance was only 6% (3/52) (see the figure).

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Conclusions:  In contrast with data from San Francisco, the transmission of drug-resistant HIV-1 in Amsterdam has decreased over time. The discrepancy in observations might be explained by variation in sample size, sub-population, and resistance table used, but might also be explained by differences in therapy prescription and adherence. Non-B subtypes are still mainly introduced by heterosexual transmission from countries where these subtypes are prevalent.

Keywords: resistance; transmission; HIV-1