Outbreak of Hepatitis A Among Men Who Have Sex With Men: Implications for Hepatitis A Vaccination Strategies

In the United States, hepatitis A remains one of the most frequently reported diseases that is preventable by vaccine; the vaccine was licensed in 1995. Recognized risk factors include contact with an infected person, contact with a day care center, use of illicit drugs, being a man who has sex with men (MSM), and international travel. Of reported cases, however, 40 percent to 50 percent do not involve a recognized risk factor.

Among MSM in the United States, Canada, Europe and Australia, periodic hepatitis A outbreaks have been reported during the past three decades. In 1996, the Advisory Committee on Immunization Practices recommended hepatitis A vaccination for sexually active MSM. Between January and March 1999, the Columbus city and Franklin County, Ohio, health departments noted an increase in hepatitis A cases compared to previous years, and MSM were disproportionately infected. Researchers studied the community-wide outbreak, evaluated the risk factors for hepatitis A among MSM, and looked for potential opportunities to deliver the hepatitis A vaccine to MSM.

Between Nov. 1, 1998 and May 30, 1999, 136 hepatitis A cases were reported to the health departments (13.7 cases per 100,000 population) -- a 325 percent increase over the average of 32 cases reported during the same period for each of the previous five years. Eighty percent of patients were white; 87 percent were male; and their median age was 33. Case patients were men who tested positive for immunoglobulin M antibody to hepatitis A virus (HAV) and identified as MSM. Control subjects were recruited from local settings popular with MSM and matched to case subjects by 10-year age group; controls had no history of hepatitis A or hepatitis A vaccination.

There was no association between hepatitis A and the number of sex partners: 10 case patients (21 percent) reported no sex partners; 24 (51 percent) reported one sex partner; and 13 (28 percent) reported more than one sex partner in the referent exposure period. There was no association between hepatitis A and anonymous sex, visiting a bathhouse, or specific sex practices, such as digital-anal or oral-anal sex.

Among MSM, household or sexual contact with a hepatitis A case patient was the only risk factor associated with hepatitis A, but this exposure accounted for a small proportion of cases -- six, or 13 percent. The researchers were not able to evaluate the possible contribution of nonsexual potential sources of HAV transmissions, such as food borne exposures. In a typical community-wide hepatitis A outbreak, a single risk factor rarely accounts for the majority of cases, and even after considerable investigation, a source cannot be identified for a considerable proportion.

"The results of our investigation and those of other studies suggest that risk factors that promote the transmission of HAV among MSM may vary and that, at least in some MSM communities, the majority of hepatitis A cases cannot be attributed to specific high-risk sex practices," the authors wrote. "...Our findings indicate that HAV transmission can occur among MSM who do not report any sexual activity during the incubation period and suggest that all MSM, regardless of their reported sexual practices, should receive hepatitis A vaccine."

Few participants, the authors noted, were aware of the hepatitis A vaccine or had been recommended it, "and we excluded only six potential control subjects who reported having received hepatitis A vaccination."

"The majority of participants had medical insurance and regular access to health care, had disclosed their sexual preference to their provider, and reported that they would have been willing to be vaccinated had it been recommended," the authors concluded. "To improve hepatitis A and B vaccination coverage among MSM, providers should be made aware of the importance of vaccinating their MSM patients, and patients should be made aware of the vaccine's availability and the importance of requesting it when they seek routine health care."

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