More than 600 people said they got sick after eating at a Chipotle outside Columbus, Ohio, health officials said Monday. And they still don’t know what has caused it.

The Delaware General Health District began investigating the restaurant, located in Powell, Ohio, on July 31 after it received numerous reports from patrons who ate there between July 26 and July 30. The location was briefly closed for an investigation.

On Aug. 3, health officials put out an update saying that they had received nearly 700 inquires and had interviewed over 500 people.

On Monday, they provided another update on Twitter saying that officials had identified 624 people who had “self-reported gastrointestinal symptoms.”