All 11 Taco Bells implicated in an E. coli outbreak used the same food distributor, the restaurant chain said Tuesday as health officials tried to pinpoint the source of the bacteria that sickened at least three dozen people.

Nine people remained hospitalized in New Jersey and New York, including an 11-year-old boy in stable condition with kidney damage.

Taco Bell Corp., a subsidiary of Yum! Brands Inc., said it had sanitized its nine closed restaurants. At least five — all in Long Island, N.Y. — had reopened by Tuesday evening.

"We have no indication what the source is. We're looking into all possibilities," spokesman Rob Poetsch said.

The distributor, Texas-based McLane Co., said Taco Bell representatives and state and federal health inspectors toured the distribution center in Burlington, N.J., that supplied the eight Long Island restaurants and the three in New Jersey.

"It involves tracking your way back and trying to see if by process of elimination you can determine the root cause," said Bart McKay, a lawyer for McLane.

He said McLane distributes to all Taco Bells in New Jersey and in the New York City area, but he had no estimate on how many that is.

The case has underscored the risk of widespread outbreaks of food poisoning at fast-food chains.

"Fast-food restaurants don't purchase ingredients down the street at the local farmers market. They purchase food nationally, process it nationally and ship it across the country," said Carol Tucker Foreman, head of the Food Policy Institute at the Consumer Federation of America.

However, Taco Bell ships its beef-and-bean fillings to restaurants pre-cooked and pre-seasoned to save money, and industry experts said that practice may be safer, because the food is handled by fewer people and is heated twice — once at the plant and once at the individual restaurants.

New Jersey health officials said their investigation would probably focus on produce, not just meat, because some of the 23 people who ate at New Jersey Taco Bells and were infected with E. coli were vegetarians.

E. coli is found in the feces of humans and livestock. Most E. coli infections are associated with undercooked meat. The bacteria also can be found on sprouts or leafy vegetables such as spinach. The germs can be passed from person to person if they do not thoroughly wash their hands after using the bathroom.

New Jersey's health commissioner has said the most recent case of E. coli was reported Nov. 29, so the danger of infection may have passed.

Two of the 11 restaurants implicated — both in New Jersey — were inspected and remained open.

Also Tuesday, the Pennsylvania Health Department said it was investigating an E. coli outbreak that sickened four people in suburban Philadelphia to determine if it was linked to the New York and New Jersey outbreak.

Three of those who fell ill at the end of November had eaten at a Taco Bell, department spokesman Troy Thompson said. Two were hospitalized and released.

E. coli, or Escherichia coli, is a common and ordinarily harmless bacteria, but certain strains can cause abdominal cramps, fever, bloody diarrhea, kidney failure, blindness, paralysis, even death.

Foreman criticized the company and health officials because they learned about the first case of E. coli Nov. 28 but did not close the last of the restaurants until two days later.

"This is a killer bug. This is more than just a belly ache," she said. "The minute they discovered they had more than one case, that's when they should start going into high gear."

In New York, Irene Abbad stopped at a Taco Bell on Long Island on Tuesday, but she was afraid to eat the food and ordered only a soft drink.

After hearing about the outbreak, she called her son, who she said is a frequent Taco Bell customer. "I said, 'Don't eat Taco Bell for a while."'

Earlier this year, three people died and more than 200 fell ill from an E. coli outbreak that was traced to packaged spinach grown in California.