Roughly one in five gay and bisexual men in 21 U.S. cities is HIV positive—and nearly half don't even know it, according to a study of 8,153 men presented by the Centers for Disease Control (CDC) and reported by Reuters. Black men and men of low socio-economic status are most likely to be infected, while young men—especially young black men—are less likely to know that they're infected. The CDC recommends that men who have sex with men get tested for HIV each year, and that those who have multiple partners or who use drugs during sex get tested every three to six months.

To read the Reuters story, click here.