The guidelines, issued by the U.S. Centers for Disease Control and Prevention and the U.S. Public Health Service, involve the use of pre-exposure prophylaxis or PrEP, a strategy in which at-risk individuals take a daily dose of an antiretroviral drug to reduce their risk of HIV infection.

The strategy builds on a landmark 2010 study that found Gilead Sciences Inc’s Truvada – a pill already widely used to treat the human immunodeficiency virus – was more than 90 percent effective at preventing HIV infections among test subjects who took the drug as prescribed.

According to the new guidelines, healthcare providers should consider PrEP for anyone who meets specific risk criteria, such as being in a relationship with an HIV-infected partner or having sex without condoms with partners known to be at risk for HIV, such as injecting drug users.

The guidelines offer the first comprehensive guidance from the CDC, replacing interim guidance that emerged after studies showed PrEP to be effective in different patient populations.

The CDC now estimates as many as 275,000 uninfected gay men and 140,000 heterosexual couples, in which one partner is HIV-infected, could benefit from PrEP.

Some 1.2 million people in the United States live with HIV, and new infections are estimated at 50,000 each year.