According to the Saint Louis Post-Dispatch, federal health investigators from the Centers for Disease Control and Prevention are in St. Louis to help determine the source and scope of the E. coli outbreak that has so far sickened at least 23 people across the region.

Local hospitals started reporting E. coli infections on Monday in St. Louis and in St. Louis, Jefferson, St. Charles and St. Clair counties.

St. Louis County health officials confirmed that the source of the E. coli O157 strain was foodborne, and there were signs that a local grocery chain may be involved. Schnucks stores across the region voluntarily replaced or removed some lettuce in salad bars, a company spokeswoman said.

Three of the infected people who have been contacted by the Post-Dispatch said they had recently eaten at salad bars from Schnucks stores in downtown St. Louis, Ladue and High Ridge.