Dr. Amon and colleagues credited the viral sequencing techniques with helping them to identify the relationships between the outbreaks in four separate locations, and to define the scope of the outbreaks quickly. The sequencing allowed them to determine if cases reported in other states were related to the four original outbreaks and provided reassurance that a larger outbreak was not occurring. The molecular epidemiologic methods also enabled public health officials to respond quickly to the later Pennsylvania outbreak. As a result, consumers were warned of the potential risk, and entry of green onions from four Mexican farms into the state was banned.
"This research highlights the role of viral sequence analysis in improving our overall understanding of the roughly 50 percent of hepatitis A cases in the U.S. that are from an unknown source," Dr. Amon said. "Just as the E. coli-contaminated beef outbreaks in the early 1990s prompted changes in epidemiological surveillance that have increased our knowledge of foodborne bacteria, the 2003 hepatitis A outbreaks demonstrated the potential for integrated molecular surveillance to provide a better understanding of the epidemiology of hepatitis A and facilitate rapid responses to outbreaks."