Federal health officials recommended Wednesday that hundreds of thousands of Americans at risk for AIDS take a daily pill that has been shown to prevent infection with the virus that causes it.

If broadly followed, the advice could transform AIDS prevention in the United States — from reliance on condoms, which are effective but unpopular with many men, to a regimen that relies on an antiretroviral drug.

It would mean a 50-fold increase in the number of prescriptions for the drug, Truvada — to 500,000 a year from fewer than 10,000. The drug costs $13,000 a year, and most insurers already cover it.

The guidelines tell doctors to consider the drug regimen, called PrEP, for pre-exposure prophylaxis, for gay men who have sex without condoms; heterosexuals with high-risk partners such as drug injectors or male bisexuals who have unprotected sex; patients who regularly have sex with anyone they know is infected; and anyone who shares needles or injects drugs.