An upscale restaurant at Fashion Island, California, that bills itself as a healthy living establishment is at the center of a suspected foodborne illness outbreak involving at least six victims, county officials said Thursday.

The sickened diners tested positive for shigella, an intestinal bacteria that triggers severe diarrhea. The “common factor” for each victim was they ate a meal at True Food Kitchen in Newport Beach on Aug. 21, 23, 24 and 25, county healthy officials said.

The county shut the restaurant Aug. 28 to investigate the outbreak. None of the victims ate the same dish, leading investigators to believe that the bacteria was spread “person to person,” said Denise Fennessy, director of Environmental Health at the county’s Health Care Agency.

“There was no common food item to focus on,” she said.

Though the case is still under investigation, True Food was allowed to reopen Saturday night after meeting certain criteria, including sanitizing the entire restaurant and bringing in replacement staff, Fennessy said.

Anita Walker, vice president of marketing for parent company Fox Restaurant Concepts in Arizona, said the “health and safety of our guests and employees are our first priority.”