NEW YORK—Infection rates for the virus that causes AIDS rose over the past six years among gay men under 30, New York City health officials said Sept. 11.

New diagnoses of HIV among gay men in that demographic increased by 33 percent during the past six years, from 374 in 2001 to 499 in 2006, said a report released by the city’s Department of Health and Mental Hygiene.

Gay males aged 13 to 19 also saw an increase in HIV rates: from 41 new cases six years ago to 87 in 2006.

The majority of new cases were among black and Latino gay men; more than 90 percent of young gay men under age 20 diagnosed with HIV were from either group, the report said.

Health Commissioner Thomas Frieden urged young men to reduce the number of partners they have and to protect themselves and their partners by using condoms more consistently.

He said a generation of young men is growing up without having seen their friends die of AIDS, which may be giving them a false “impression that HIV is not such a terrible infection.”