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| http://www.sciencedaily.com/release...50921075332.htm
http://www.idsociety.org/
Novel use of genetic testing methods helped public health officials control and
limit the further spread of four outbreaks of foodborne hepatitis A virus in
2003 related to the consumption of green onions, according to a detailed
analysis published in the October 15 issue of The Journal of Infectious
Diseases, now available online.
The authors of the study, Joseph J. Amon, PhD, MSPH, and colleagues at the
Centers for Disease Control and Prevention (CDC), explained that these molecular
epidemiologic methods had not previously been used in an ongoing investigation
of a hepatitis A virus outbreak. The methods, involving genetic sequencing
analysis of virus found in blood samples from infected individuals, have greatly
improved understanding of outbreaks of other foodborne pathogens, but are
time-consuming and not widely available.
In September 2003, Tennessee, North Carolina, and Georgia reported a total of
422 cases of foodborne hepatitis A virus infection to CDC. Preliminary
investigations suggested clustering of reported cases among patrons of three
unrelated restaurants. Investigators identified green onions as the likely
culprit in the outbreak by interviewing infected and uninfected restaurant
patrons. In addition to these standard techniques, the researchers also compared
viral RNA sequences from case patients and individuals concurrently ill with
hepatitis A virus infection in non-outbreak settings in the United States and
Mexico.
Viral RNA sequences from patients in the three states, plus patients involved in
a subsequent outbreak in Pennsylvania in October 2003 (the latter recently
described in the Sept. 1 issue of the New England Journal of Medicine), were
slightly different from each other. The viral sequence from each outbreak,
however, was identical to one or more sequences isolated from northern Mexican
residents infected with hepatitis A virus. The researchers concluded that the
sources of the green onions served in restaurants in Tennessee and Georgia were
three farms in northern Mexico.
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."
Alan
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