WASHINGTON – Americans will soon be able to test themselves in the privacy of their own homes for the virus that causes AIDS, now that the Food and Drug Administration has approved the first rapid, over-the-counter HIV test.

The OraQuick test detects the presence of HIV antibodies using a mouth swab and returns a result in 20 to 40 minutes.

Government officials estimate that about 240,000 people, or one-fifth of the roughly 1.2 million people carrying HIV in the U.S., don’t know they are infected. Testing is a chief means of slowing new infections, which have held steady at about 50,000 per year for two decades.