While the U.S. annual HIV diagnosis rate dropped by a third over the past decade, the rate mostly rose among gay men, more than doubling among those between 13 and 24, HealthDay reports. Publishing their findings in The Journal of the American Medical Association (JAMA), researchers at the Centers for Disease Control and Prevention (CDC) analyzed data, covering 2002 to 2011, from the agency's National HIV Surveillance System.

During that time period, 493,372 Americans were diagnosed with HIV. The annual rate of diagnosis fell by 33.2 percent across the decade, from 24.1 per 100,000 in 2002 to 16.1 per 100,000 in 2011. The rates fell in almost all categories. Among women, the rates fell by around half. Blacks and Hispanics saw respective 37 percent and 41 percent declines. Rates of new infections acquired from injection drug users declined by about 70 percent, and those from heterosexual sex dropped by over one third.

Gay men, however, bucked the trend. Rates increased among men who have sex with men (MSM) in the 13 to 24, 45 to 54 and over 55 age brackets, while dropping in the 35 to 44 category. The rate of increase was the most alarming among the youngest group, which saw diagnoses increase from about 3,000 to 7,000 per year.

The study is limited by the fact that it measures diagnoses, as opposed to actual new cases. Thus, the figures can over-estimate how much HIV affects a particular group if that group tends to get tested at a relatively higher rate. However, the testing rates among young MSM is relatively low.

The study authors projected: “Among men who have sex with men, unprotected risk behaviors in the presence of high prevalence and unsuppressed viral load may continue to drive HIV transmission.”

To read the JAMA summary, click here.

To read the HealthDay report, click here.