The New Face of Hepatitis A
Abstract & Commentary
By Mary Elina Ferris, MD, Clinical Associate Professor, University of Southern California. Dr. Ferris reports no financial relationship to this field of study.
Synopsis: Hepatitis A has been greatly reduced in the United States due to widespread vaccination, and most new cases are now the result of international travel.
Source: The evolving epidemiology of hepatitis A in the United States. Arch Intern Med 2010;170:1811-1818.
Hepatitis a continues to be a significant illness, with an estimated 1.4 million new cases worldwide. In developing countries, children develop immunity after infection, so outbreaks are infrequent. In other countries, where children do not become immune from natural exposure, adult populations are susceptible and outbreaks can occur, including many countries in the European Union.
The U.S. Centers for Disease Control and Prevention (CDC) recruited states covering 30 million persons to participate in the Emerging Infections Program (EIP), which involved molecular testing of hepatitis A virus strains to more thoroughly describe the infections that do occur in the United States. For the years 2005-2007, 1156 cases of hepatitis A were reported, and 49% were from New York City. Of these, 39% were Hispanic. Most cases occurred in urban areas. The most common source of infection was international travel or being exposed to a traveler, with Mexico being the most common associated source. For patients reporting travel as their only known risk factor, 86 of 108 cases were traveling to their county of native birth. One outbreak in Minnesota was associated with a foodborne outbreak, but most others involved international travel as the most likely source. This was confirmed with molecular analysis, which showed that the strains from the travel-related cases were very similar to strains in the countries where the travel occurred.
Before vaccination was available for hepatitis A, only 4% of U.S. cases were associated with international travel; now 46% of cases are travel-related. The national vaccination strategy was expanded to all children age 2 years and older in 1999; by 2003, this resulted in a 76% decline in the incidence of hepatitis A overall, and an 87% decline in incidence among children age 2-18 years. Since 2006, national recommendations for hepatitis A vaccine include all children age 12 months or older in the United States.
Commentary
This is a remarkable success story for the reduction of hepatitis A in the United States, from approximately 26,000 or more annual cases before the vaccine to only 600 cases during this study period. The disease in adults can cause major morbidity and even fatal liver failure. An interesting consequence of this success is that the disease now has a different epidemiology, changing from outbreak-associated to mainly sporadic cases associated with international travel.
It's important for clinicians to understand this change in the incidence of hepatitis A, because it means that preventive strategies must target international travelers as well as universal childhood immunization. The most high-risk group is persons returning to their native countries to visit family and friends.1 Tourists and business travelers had a lower risk of infection. Ongoing surveillance of hepatitis A continues to be important so that we can understand where and when it occurs, and respond appropriately.
References
1. Anderson KL. Hepatitis A: A traveling target. Arch Intern Med 2010;170:1818-1819.
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