In our view, candidate environmental factors should include anal sexual behaviors, especially receptive anal intercourse, that can deposit. The Relation between Nitrite Inhalants, Unprotected Receptive Anal Intercourse, and the Risk of Human Immunodeficiency Virus Infection. Anal sex or anal intercourse is generally the insertion and thrusting of the erect penis into a .. Unprotected receptive anal sex (with an HIV positive partner) is the sex act most likely to result in HIV transmission. Other infections that can be.