Department of Biology, Hopital de Versailles, 177 Rue de Versailles, Le Chesnay 78150, France.
We report a case of human immunodeficiency virus type 1 group O infection not detected by two highly sensitive immunoassays. The sera were strongly reactive to the V3 peptide of group O but not to the gp41 immunodominant epitope. Gp41 was sequenced, confirming that this virus belonged to group O.