Diagnosis rate for HIV falls by a third in U.S.: researchers
About 2880 candles are seen lit during a World AIDS Day event in Jakarta

WASHINGTON (Reuters) - The annual rate of diagnosis with HIV, the virus that causes AIDS, fell by a third in the United States between 2002 and 2011, researchers reported on Saturday.

Fewer people in all U.S. groups tested positive for human immunodeficiency virus except for gay and bisexual men ages 13 to 24 and over 45, they wrote in a special issue of the Journal of the American Medical Association.

"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," the report said.

From 2002 to 2011, 493,372 people were diagnosed with HIV in the United States, researchers said, citing data from the 50 states and the District of Columbia.

The diagnosis rate fell to 16.1 per 100,000 people in 2011 from 24.1 in 2002, the researchers wrote in the issue, published to coincide with an international AIDS meeting in Melbourne, Australia.

The U.S. drop is in line with a global downturn in the epidemic of AIDS, or Acquired Immune Deficiency Syndrome. The United Nations said on Wednesday that there were 2.1 million new HIV infections worldwide in 2013, down 38 percent from 2001.

The U.S. decline followed increased emphasis on care and treatment for people with HIV, including use of antiretroviral therapy, the report said.

The researchers were headed by Anna Satcher Johnson, an epidemiologist with the U.S. Centers for Disease Control and Prevention (CDC).

The CDC has reported that 1.1 million people in the United States are living with HIV, and 18 percent are unaware of their infections.

(Reporting by Ian Simpson; Editing by Bernard Orr)