Although the source of bagged, chopped iceberg lettuce delivered to Aunt Mid’s had yet to be identified. A good guess would be California this time of the year, specifically the Salinas Valley (See growing season data).  Aunt Mid’s is ready to point the finger – from its website:

The health alert has identified Aunt Mid’s as one of the wholesale processors who sold institutional-sized iceberg lettuce product to the establishments which served the affected persons. It is expected that other wholesale suppliers will also be identified as and when product traceback measures are finalized.

As I have said before, E. coli O157:H7 outbreaks associated with lettuce or spinach, specifically the "pre-washed" and "ready-to-eat" varieties sold under various brand and trade names, are by no means a new phenomenon. By way of illustration:

— in October 2003, thirteen residents of a California retirement home were sickened, and two people died, after eating E. coli-contaminated, pre-washed spinach;

— in September 2003, nearly forty patrons of a California restaurant chain fell ill after eating salads prepared with bagged, pre-washed lettuce; and

— in July 2002, over fifty young women fell ill with E. coli O157:H7 at a dance camp after eating "pre-washed" lettuce, leaving several hospitalized and one with life-long kidney damage.

And this is just a small sampling of the twenty or more E. coli O157:H7 outbreaks since 1995 in which spinach or lettuce was the source.  Several more outbreaks linked to contaminated leafy-produce, including most recently the September 2005 Dole packaged lettuce outbreak, are identified in the chart below:

Aug. 1993 Salad Bar E. coli O157:H7 53 WA

July 1995 Lettuce (leafy green; red; romaine) E. coli O157:H7 70 MT

Sept. 1995 Lettuce (romaine) E. coli O157:H7 20 ID

Sept. 1995 Lettuce (iceberg) E. coli O157:H7 30 ME

Oct. 1995 Lettuce (iceberg; unconfirmed) E. coli O157:H7 11 OH

May-June 1996 Lettuce (mesclun; red leaf) E. coli O157:H7 61 CT, IL, NY

May 1998 Salad E. coli O157:H7 2 CA

Feb.-Mar. 1999 Lettuce (iceberg) E. coli O157:H7 72 NE

July-Aug. 2002 Lettuce (romaine) E. coli O157:H7 29 WA, ID

Oct. 2003-May 2004 Lettuce (mixed salad) E. coli O157:H7 57 CA

Apr. 2004 Spinach E. coli O157:H7 16 CA

Sep. 2005 Lettuce (romaine) E. coli O157:H7 32 MN, WI, OR

The most recent major E. coli outbreak tied to leafy greens was the Dole Spinach outbreak of 2006. This nationwide outbreak included 205 illnesses due to E. coli O157:H7 reported the CDC. This  included 31 cases of HUS, 102 hospitalizations, and 3 deaths. The FDA concluded that all the implicated spinach was traced back to Salinas Valley in California.  Another outbreak that sickened 10 occurred in May 2008 in the State of Washington. The illnesses were linked to bagged, Romaine lettuce (See complete list of leafy green outbreaks).