A report released Wednesday by the Centers for Disease Control and Prevention indicates 57% of men who have sex with men (MSM) reported having unprotected anal intercourse at least once in the last 12 months. That's a major jump from seven years ago, when the number was 48%.

Approximately 50,000 Americans are infected with HIV each year: Gay men account for 65% of those infections even though they represent only 2%-5% of the total population.

Why there's a jump isn't clear—it may be due to improved treatments lessening the fear of infection, or lowering the viral load of those infected. Or it may be because men are increasingly having sex with partners who they believe have the same HIV status as they do.

The CDC study also indicated men who are not aware of their HIV status are much more likely to have unprotected anal sex: Only 67% of men having sex with other men reported getting tested within the past year.

"We think that testing is one our greatest weapons," researcher Gabriella Paz-Bailey told Reuters. "We know that when men are tested and know their status they are likely to change their behavior."