Officials initially believed the infectious liver disease was spread by a Chi-Chi's Restaurant employee who failed to wash his hands before touching food.
However, Pennsylvania health officials said Wednesday that they are now unable to determine the exact source of the outbreak, and are looking into a number of possibilities, including contaminated green onions that sickened people in Georgia, North Carolina and Tennessee in September.
"There's a bit of frustration on our part," said Richard McGarvey, a spokesman for the Pennsylvania Health Department.
Infectious disease experts say finding the source of the virus can be challenging because hepatitis A has a long incubation period.
Unlike the more serious variants, hepatitis B and C, which are generally spread by intravenous drug use or risky sexual behaviors, hepatitis A is spread by eating something contaminated with the feces of someone with hepatitis A, according to the Centers for Disease Control and Prevention. Food-borne outbreaks generally involve fresh vegetables or other uncooked foods handled by a contaminated person, but the disease is relatively rare.
"The longer we go without identifying a source makes it less likely they're going to identify a source," said Dr. Lee Harrison, director of the Public Health and Infectious Diseases Laboratory at the University of Pittsburgh.
While Pennsylvania health officials began warning the public of the outbreak Nov. 3, people were found to have contracted the disease as far back as Sept. 20, McGarvey said. One man who contracted the disease from the restaurant died last week.
The restaurant, about 25 miles northwest of Pittsburgh, voluntarily closed Nov. 2. Louisville, Ky.-based Chi-Chi's announced it plans to keep the restaurant closed for at least 60 days.
Contaminated green onions are suspected as the source of a string of hepatitis A outbreaks in September in Georgia, North Carolina and Tennessee.
In Georgia, about 250 people became infected when contaminated green onions were shipped to a dozen restaurants in the northern half of the state, said Richard Quartarone, a spokesman for the state's Division of Public Health.
Quartarone said the U.S. Food and Drug Administration is now trying to trace the cause of the green onion contamination.
Dr. Allen Craig, state epidemiologist for Tennessee Department of Health, said when about 80 people contracted hepatitis A after eating green onions at a restaurant near Knoxville, Tenn., investigators began interviewing some 300 people using 12-page questionnaires.
Meanwhile, a couple who claimed to have been infected after dining at the Pittsburgh restaurant Oct. 5 filed a negligence lawsuit Wednesday, claiming Chi-Chi's failed to notify them of the outbreak.
Company representatives declined to comment on the lawsuit.
Hepatitis A causes flu-like symptoms that may include fever, nausea, diarrhea, jaundice, fatigue, abdominal pain and loss of appetite. The infectious liver disease usually clears up in about two months.