The occurrence of human immunodeficiency virus type 1 (HIV-1) dual infections in Amsterdam, The Netherlands, was examined during 2003-2007 to investigate whether the number of HIV-1 dual infections increased as the number of HIV-1 infected individuals increased during the same period. All first HIV-1 genotyping sequences obtained from 2003 through 2007 were retrieved and examined for the number of degenerate base codes in the reverse-transcriptase fragment. A total of 72 patients had >or=34 degenerate base codes; for these patients, a fragment of the V3-V4 region of the env gene was amplified, cloned, and sequenced to verify the presence of an HIV-1 dual infection. The number of dual infections were counted for each year investigated. No significant change in the incidence of dual infections was observed in our population of patients, who were selected on the basis of the number of degenerate base codes in each patient's first HIV-1 sequence obtained from 2003 through 2007. The frequency of HIV-1 dual infections varied between 1.0% and 2.4% each year, with no significant trend over time (P = .49). Patients with HIV-1 dual infections were similar to patients with single HIV-1 infections in The Netherlands with regard to distribution of risk group, sex, and HIV subtype. The proportion of HIV-1 dual infections in The Netherlands did not increase from 2003 through 2007, although the HIV-1-infected population expanded in this period.
