By Jennifer Bails
TRIBUNE-REVIEW
Thursday, September 29, 2005
Health officials responded faster to the hepatitis A outbreak in Beaver County two years ago because genetic tests used during the outbreak produced results within a few days, according to a new state and federal report.
A technique called viral sequencing enabled the U.S. Food and Drug Administration to launch an immediate investigation to see if green onions imported from Mexico caused the outbreak that sickened 660 people and killed four, according to an analysis to be published in the Oct. 15 issue of The Journal of Infectious Diseases, but now available online.
Without this molecular evidence, the FDA couldn’t have begun tracing the source until medical detectives finished interviewing hepatitis A patients about their symptoms and what foods they ate and where, said Dr. Anthony Fiore, a medical epidemiologist at the U.S. Centers for Disease Control and Prevention in Atlanta.

“In this case, we were able to make a presumed link between the green onions from growers in northern Mexico within a few days of the start of the outbreak just based on viral sequencing alone,” Fiore said. “As a result, the FDA could get their traceback investigation started sooner, which led them to put a shipping ban on produce grown by four farms.”
That success could lead to more widespread use of viral sequencing to track disease outbreaks, Fiore said. Similar methods already are used routinely for genetic comparison of bacteria linked to E. coli and salmonella poisoning.
Viral sequencing determines the exact order of the chemical units that make up the genetic code of a virus. With hepatitis A, the genetic code consists of units called RNA, which is structured similar to DNA. Some parts of the RNA sequence vary slightly from strain to strain. Scientists compare the variations to tell how closely one viral strain is related to another.
Technology has emerged only within the last decade to sequence RNA fast enough to be used during a hepatitis A outbreak rather than afterward, Fiore said.
In the past five years, scientists also learned how to extract virus samples suitable for sequencing from blood serum, he said. Previously, stool samples were required, which was slower.
“The technology has advanced enough that now we can get results from viral sequencing in less than two days,” Fiore said.
In September 2003, Tennessee, North Carolina and Georgia reported 422 cases of foodborne hepatitis A virus infection to the Centers for Disease Control and Prevention. Through patient interviews and viral sequencing, CDC officials determined those cases were linked to consumption of contaminated green onions, possibly imported from Mexico.
They were wrapping up the investigation in early October as patrons of Chi-Chi’s restaurant in Beaver County Mall unknowingly ate contaminated green onions.
While epidemiologists began interviewing patients in the Beaver County area, CDC scientists began sequencing viral strains isolated from their blood.
While the interviews were underway, researchers discovered the RNA sequence of the hepatitis A strain in Pennsylvania patients differed by just one chemical unit from the virus in the Georgia and North Carolina outbreaks. And it differed by a single unit from the Tennessee virus.
“That alone didn’t prove it had to be related to the same source, but it was good preliminary evidence that jump-started the whole process more quickly,” Fiore said.
Jennifer Bails can be reached at jbails@tribweb.com or (412) 320-7991.