HIV-positive men who have sex with other men (MSM) are at a high risk of contracting the Hepatitis C virus through sex, according to a new study of men in New York City.

Sexual transmission of the virus is considered rare. However, in late 2005, two HIV-infected MSM having acute Hepatitis C infection suspected of being sexually transmitted, were evaluated at the Mount Sinai Medical Center in New York City.

This prompted the medical center to request referrals of similar patients.

Between October 2005 and December 2010, researchers identified 74 HIV-infected MSM who recently got the Hepatitis C virus infection. But no reported history of injection-drug use was evaluated in these men, according to the study.

The results are published in the July 22 edition of the Centers for Disease Control and Prevention's Morbidity and Mortality Weekly Report.

Twenty-two case patients were compared to a group of 53 controlled subjects. They were all asked to complete self-administered questionnaires about their sexual practices and drug use during the 12 months prior diagnosis (for case patients) or preceding the questionnaire (for controlled subjects). Researchers found that the men who had recently gotten the Hepatitis C virus infection were 23 times more likely to have had unprotected anal sex with men.

Furthermore, the Hepatitis C virus genetic analysis suggested that the virus was passed on within social networks of these men.

While Hepatitis C is rarely transmitted among stable heterosexual couples, this is clearly not the case among HIV-infected MSM in New York City, said Dr. Daniel Fierer, assistant professor of medicine and infectious diseases at Mount Sinai School of Medicine. MSM, and to some extent their health care providers are generally not aware that having unprotected receptive sex can result in [hepatitis C virus] infection.

The CDC describes Hepatitis C is a contagious liver disease resulting from infection with the Hepatitis C virus. It can range from a mild illness lasting a few weeks to a serious, lifelong illness.

Hepatitis C is usually spread when the blood from an infected person enters the body of someone who is not infected. Most people today become infected with the virus by sharing needles or other equipment to inject drugs, according to the CDC.

There are an estimated 3.2 million Americans living with chronic Hepatitis C virus infection, according to the CDC.

The U.S. will observe World Hepatitis Day on July 28 at a White House event.

Though the role of sexual transmission of Hepatitis C virus hasn't been well defined, reports over the past decade, mainly from Europe, have implicated sexual transmission of the virus among HIV-infected men who have sex with men, according to the study.

Fierer said the good news is that the cure rate for new hepatitis C virus infections is very high with early treatment. He added that without regular testing of the men at risk, infections may be missed and the high cure rate lost.

Our study suggests that HIV-infected MSM should take steps to protect themselves and others by using condoms, Dr. Fierer said. Also, health care providers should be screening these men for hepatitis C, and public education and outreach programs should include information about these risks.