The number of people sickened in an E. coli outbreak traced to a suburban Chicago restaurant continues to increase, with 65 now confirmed. Twenty of the victims’ symptoms were so severe they were admitted to hospitals.

Public health officials have not yet determined the root cause of the outbreak, which was traced to the Carbón Live Fire Mexican Grill location on 26th Street in the suburb of Bridgeport. The restaurant remains closed, according to Matt Smith, a spokesman for the Chicago Department of Public Health.

logo Carbon Live Fire Mexican Grill“As part of our comprehensive investigation, we have taken and tested numerous samples from the restaurant and have tested staff,” Smith said Thursday. He did not say whether the department had the test results yet.

It remains unknown when exactly the health department became aware of the outbreak. The department posted a news release about the outbreak July 1, but has not posted an update since then.

The restaurant’s owners voluntarily closed the Carbón Live Fire Mexican Grill, according to the July 1 news release. A second Carbón Live Fire Mexican Grill on North Marshfield was also voluntarily closed, but the health department cleared it and the owners reopened.