Three people infected with the virus have died, and thousands have lined up for inoculations since the outbreak was reported in early November among people who ate at a Chi-Chi's Mexican restaurant.
Many area residents have apparently given up eating out for the time being, as a precaution.
Five doctors from the state Department of Health and roughly 35 state public health nurses, five investigators from the Centers for Disease Control and five Department of Agriculture officials have been painstakingly reviewing menus and interviewing and re-interviewing people who ate at Chi-Chi's to trace the source of the outbreak, the Pittsburgh Post-Gazette reported Sunday. Agriculture officials have traced the strain of the virus back to Mexico, the Post-Gazette reports.
A Chi-Chi's executive said the company has adopted "extraordinary measures" companywide, including sickness logs for employees and asking workers to sign "wellness statements" asserting they are not ill, in an effort to prevent similar outbreaks elsewhere.
As of Saturday, 510 cases of hepatitis A had been confirmed in the outbreak, Pennsylvania Health Department spokesman Richard McGarvey said.
He said more infections are expected because people who contract hepatitis A typically don't exhibit its early flu-like symptoms for 28 to 30 days.
The state offered antibody inoculations to anyone who ate at the restaurant after Oct. 22 — the latest date such shots could help since they must be administered within two weeks of exposure. That means people exposed before Oct. 22 could still start showing symptoms through next weekend. The virus can lead to liver failure.
"We still haven't reached that date, when all those inoculations are going to help," McGarvey said Saturday. After Nov. 22, health officials expect the number of new infections to level off and eventually stop, he said.
About 8,500 people received the shots because of the outbreak linked to a Chi-Chi's at the Beaver Valley Mall, about 25 miles northwest of Pittsburgh.
Officials at the mall said sales at the food court were off by as much as 40 percent and sales throughout the mall were down up to 25 percent.
"I won't go to Chi-Chi's again," Barbara Barrickman said as she shopped at the mall. "I know that's unfair, but that's just how I feel."
All 60 employees of that restaurant will remain under medical supervision until each has been medically cleared, said Bill Zavertnik, chief operating officer at Louisville, Ky.-based Chi-Chi's. The restaurant is closed until Jan. 2.
Eleven employees who tested positive for hepatitis A remain under medical care and the rest were given antibodies, Zavertnik said.
The company already certifies its managers in food handling safety, in addition to the new employee health measures initiated at all of its restaurants, scattered from Minnesota to the mid-Atlantic states.
Zavertnik said Chi-Chi's food purchasers are cooperating with investigators to identify the source of the outbreak and the company has hired an outside medical expert to work with the federal Centers for Disease Control and the Pennsylvania Department of Health.
Health investigators say they still don't know the source of the virus. They're looking at foods, including green onions, which are difficult to clean and have been linked to smaller outbreaks in other states.
Chi-Chi's removed green onions, or scallions, from all of its restaurants as a precaution, Zavertnik said.
Richard Quartarone, a spokesman for the Georgia Division of Public Health, said that while outbreaks in September in Tennessee and Georgia, neither linked to Chi-Chi's restaurants, were believed to have stemmed from green onions, investigators don't know how the virus got there and the two cases involved different strains of the virus.
"It's possible they're connected. It could have been a grower or a contaminated water source," he said. "Was there a sewer break at the time the onions were picked? Or was it people picking and bunching them?"
Zavertnik wouldn't comment on lawsuits that have been filed as a result of the outbreak. He said he didn't know details about the restaurant's green onion supplier.
The last person to die, John C. Spratt, 46, of Aliquippa, ate chicken fajitas with his teenage daughter on Oct. 5. He ate the condiments — which included onions — but she did not, Spratt's family said.
Jacqueline Spratt, 17, developed some flu-like symptoms but recovered. Her father, who family members said was in good health, developed liver failure and died Friday.