A 15th person has tested positive for E. coli as authorities continue to investigate what caused the outbreak linked to an Orange County restaurant.

Fourteen customers and one employee at the restaurant in Lake Forest have tested positive for the dangerous bacterium, officials with the county Health Care Agency said Thursday. All were at the restaurant between March 23 and March 25. Health officials described the group as 10 children and five adults.  The latest to test positive was not hospitalized.

The restaurant remains closed while testing is completed of about 40 employees, county officials said. The source has not been determined.

Since the outbreak began, two children have been hospitalized. An 8-year-old boy was released April 3 from Children’s Hospital of Orange County. A 12-year-old girl is recovering after spending days in intensive care at the hospital.