The Centers for Disease Control and Prevention (CDC) announced that after a lengthy investigation it has concluded that a recent outbreak of E. coli O1157:H7 across 10 states was caused by Romaine lettuce grown in California.  As of December 4, 2011, 60 people have been confirmed with E. coli O157:H7 infection; 30 were hospitalized and two developed hemolytic uremic syndrome.  Cases occurred in Arizona (1), Arkansas (2), Georgia (1), Illinois (9), Indiana (2), Kansas (3), Kentucky (1), Minnesota (3), Missouri (37), and Nebraska (1).  The Missouri cases were primarily residents of St. Louis County.  All 60 culture-confirmed cases have strains of E. coli with the same DNA fingerprint, which suggested a common source.

Many of the cases identified early in the outbreak reported having purchased items at Schnucks grocery stores’ salad bars in the week before their illness. Schnucks is a grocery chain centered in St. Louis, Missouri which also has stores in Illinois, Indiana, Tennessee, Mississippi, Iowa, and Wisconsin. On October 26, the day the St. Louis Health Department identified the outbreak, Schnucks removed salad bar items linked with recent fresh produce outbreaks (such as lettuce, spinach, green onions) from salad bars across its stores and replaced them with items from other sources.   A team of epidemiologists from the CDC arrived in Missouri to assist the Missouri State Health Department with the investigation.

The investigation revealed that Ill persons had purchased salads from salad bars at Schnucks between October 5 and October 24, 2011.  Romaine lettuce on salad bars at all the locations of Schnucks grocery stores was supplied by a single lettuce processor via a single distributor.  A case with a matching DNA fingerprint was identified on a university campus in Minnesota; the campus food service received Romaine lettuce of the same lot that was distributed to the Schnucks salad bars during the period of the outbreak.  Two matching cases at a Missouri university campus were also likely linked to the outbreak, but poor record-keeping by the lettuce distributor prohibited confirmation that the implicated lot was distributed to the campus.

The Food and Drug Administration (FDA) determined that the single common lot of lettuce was harvested from a particular farm in California.  Preliminary investigation at the farm did not identify the source of the contamination.  This particular farm was no longer in production at the time of the investigation, so no product recall was issued.