(Reuters) - More than half of young people in the United States who are infected with HIV are not aware of it, according to a report by government health officials that zeroes in on one of the remaining hot spots of HIV infection in America.Young people ages 13 to 24 account for 26 percent of all new HIV infections, according to the report by the U.S. Centers for Disease Control and Prevention, which was released on Tuesday in advance of World AIDS Day on December 1."Given everything we know about HIV and how to prevent it in 30 years of fighting the disease, it's just unacceptable that young people are becoming infected at such high rates," CDC Director Dr. Thomas Frieden said on a conference call with reporters.Every month, 1,000 young people in America become infected with HIV, an incurable infection that costs $400,000 to treat over a lifetime, Frieden said. If left untreated, HIV infection leads to AIDS and early death."The data are stark and worrying," Dr. Kevin Fenton, director of the National Center for HIV/AIDS, Viral Hepatitis, STD and TB Prevention at the CDC, said in a telephone interview.In 2010, 72 percent of the estimated 12,000 new HIV infections in young people occurred in young men who have sex with men, and nearly half of new infections were among young, black males."We are particularly concerned about what is happening with HIV among young black gay and bisexual men," Fenton said. "They account for 39 percent of all new infections among youth and more than half of new infections among young men who have sex with men."Fenton said the proportion of young people infected with HIV has remained relatively stable during the last few years, but infection rates appear to be increasing in these populations.And because many of the newly infected gay or bisexual males are just beginning to explore their sexuality, stigma and homophobia are making HIV testing and treatment far more challenging.Although the CDC and the American Academy of Pediatrics recommend routine screening for HIV starting in the early teens, "too few young people are getting tested," Frieden said.Only 13 percent of all high school students and only 22 percent of sexually active high school students have ever been tested for HIV, the CDC found.The figures for young adults aged 18 to 24 are not much better, with only 35 percent of people in this age group reporting ever having been tested for HIV.