Researchers were particularly concerned about young black MSM, who were less likely to be out.

MSM who were not out were also more likely to have sex with women, therefore playing an important role in HIV transmission to women, according to the CDC report.

Researchers analyzed surveys of 5,589 MSM who were asked about their sexual practices and attitudes. The men, who were surveyed between 1994 and 2000 and were between the ages of 15 and 29, were all tested for hepatitis B and HIV.

More than 600 MSM had not disclosed their sexual orientation to anyone, and 55 percent of these men were between the ages of 15 and 22. Closeted MSM weren’t necessarily at greater risk for HIV, but they were less likely to know that they were HIV-positive.

Overall, eight percent of the nondisclosing men were HIV-positive compared to 11 percent of the MSM who were out. However, 14 percent of the closeted black MSM were HIV-positive compared to 5 percent of the closeted MSM of other races. Twenty-four percent of the openly gay or bisexual black MSM were HIV-positive.

Ninety-eight percent of the closeted MSM did not know they were HIV-positive compared with 75 percent of the MSM who were openly gay or bisexual.

“The findings that all but one HIV-infected nondiscloser were unaware of their infection is consistent with a recent report suggesting that the majority of young HIV-infected MSM do not know they are infected,” the authors wrote. “For more young HIV-infected MSM to realize the benefits of early diagnosis and care, and to help prevent further HIV transmission among young MSM and their female partners, health-care providers and federal, state, and local HIV prevention managers should expand and improve HIV testing and prevention practices to meet the needs of diverse MSM, including those who do not disclose their sexual orientation.”

Black MSM were less likely to be out -- 18 percent of black MSM were not out compared with 8 percent of white MSM. Women are also a concern when it comes to nondisclosing MSM who may not know that they are putting female partners at risk.

“The findings that more than one in three nondisclosers reported having recent female sex partners suggests that nondisclosing MSM might have an important role in HIV/STD transmission to women,” according to the report. “This might be particularly true for black nondisclosing MSM, of whom approximately one in five was infected with HBV and one in seven was infected with HIV. To help prevent further HIV/STD transmission among young MSM and their female sex partners, greater efforts are needed to increase public awareness and to develop or expand HIV/STD testing and prevention programs to meet the needs of nondisclosers, particularly those who are black.”

Indeed public education and prevention programs need to be developed directly targeting closeted MSM, according the study authors. It is necessary, the report continued, “to reduce internalized homophobia and other factors that influence nondisclosure, barriers to HIV/STD testing and prevention services, low-risk perception, and high-risk behavior, including the risk for transmission to male and female sex partners. Corresponding efforts also should be developed for women to increase knowledge of HIV/STD acquisition risks from partners who might be bisexual and of where to obtain confidential testing and prevention services for themselves and their partners.”