New Jersey ? An outbreak of E. coli bacteria has sickened at least 15 people, two seriously, in central New Jersey during the past two weeks, officials said Sunday.

Authorities had yet to determine how and where the victims, mostly children, became infected. Investigators focused on a Taco Bell restaurant in South Plainfield where 11 of the victims ate.

The restaurant, which has been closed voluntarily since Thursday, passed a health code inspection last week, and tests were being performed on stool samples from 21 of its employees.

Authorities were still looking for a few other employees from the restaurant and hoped to have results late Sunday or today.

Seven of the victims were in area hospitals Sunday night. Two had developed a serious condition called hemolytic uremic syndrome that can permanently damage the kidneys. Officials were also investigating four other cases of suspected E. coli infection.

Two of the confirmed victims were adults, while the others mostly range in age from 7 to 14, officials said.