Pittsburgh ? A third person died Friday and nearly 500 others who ate at a Chi-Chi’s Mexican restaurant have fallen ill in the biggest known outbreak of hepatitis A in U.S. history, making people so scared that many are no longer eating out and thousands have lined up for antibody shots.

Health investigators are focusing on whether contaminated produce — perhaps green onions — caused the outbreak at the restaurant in the Beaver Valley Mall, about 25 miles northwest of Pittsburgh.

“We’re very concerned. It’s very serious and we’ve sent a team of people out there to assist,” said David Daigle, a spokesman for the Centers for Disease Control and Prevention.

Health officials Friday met with worried shoppers at the mall to try to squelch rumors that the virus was spreading out of control to other restaurants in the region. State Rep. Mike Veon attended a news conference at the mall and ate a sandwich he bought there.

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.”

At least 490 people have been sickened in the outbreak — believed to be the largest on record in the United States, Daigle said.

The Chi-Chi’s has been shut down, and the restaurant chain removed green onions from kitchens at all its 100 locations, said Bill Zavertnik, chief operating officer of the Louisville, Ky.-based company.

In September, about 280 people in Georgia and Tennessee were infected with hepatitis A from contaminated green onions, including 210 people who ate at restaurants in the Atlanta area. The infections were linked to 12 restaurants — none of them Chi-Chi’s.

“We’ve taken the action to remove them based on our abundance of caution with regard to green onions,” Zavertnik said. “There’s no definitive information that green onions played a role. However, we don’t know. Authorities are looking at them.”

Customers at the Beaver Valley Mall's food court eat lunch in Monaca, Pa. A third person died Friday and at least 490 people have been sickened since a hepatitis A outbreak began last week around the Chi-Chi's restaurant at the food court. The restaurant is closed until 2004.