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To the Editor: Preexposure prophylaxis with emtricitabine (FTC)–tenofovir disoproxil fumarate (TDF) has been shown to be efficacious in preventing human immunodeficiency virus type 1 (HIV-1) infection in men who have sex with men and in whom adherence to treatment is high, as measured by levels of tenofovir diphosphate (TFV-DP) in dried blood spots.1 We describe a case of HIV-1 infection despite FTC-TDF–based preexposure prophylaxis.2
A 43-year-old man in Toronto who reported having sex with men began to receive oral daily FTC-TDF in April 2013 and had seven nonreactive fourth-generation HIV screening tests over the next 21 months. Pharmacy dispensation records provided support for his report of “perfect” adherence to preexposure prophylaxis over 24 months.
On day 0, the initial result of a combination assay to detect antibodies to HIV types 1 and 2 was...