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CDC Issues Update on Lettuce E. coli Outbreak

The federal Centers for Disease Control and Prevention (CDC) in Atlanta on May 21 issued what it said will be its final report on the E. coli O145 five-state outbreak involving romaine lettuce.

Among its top findings were:

1)  The latest case count is 26 confirmed and 7 probable cases related to this outbreak from MI, NY, OH, PA, and TN.

2)  Shiga toxin-producing E. coli (STEC) O145 is an emerging bacterial pathogen that can produce the same illness as E. coli O157, but the O145 serogroup is infrequently reported.

3) The current outbreak is the first reported foodborne outbreak identified in the U.S. due to this pathogen.

The E. coli O145 outbreak led to a May 5 recall of romaine lettuce that was sold up to May 12 under both the Freshway and Imperial Sysco brands by Ohio-based Freshway Foods.  The contaminated lettuce was likely grown in the Yuma, AZ area.

CDC said local and state public health officials in Michigan, New York, Ohio, Pennsylvania, and Tennessee are continuing to investigate human illnesses caused by Escherichia coli (E. coli) O145.

CDC and the U.S. Food and Drug Administration (FDA) are assisting at the federal level.

CDC said that as of May 20, 2010, a total of 26 confirmed and seven probable cases related to this outbreak have been reported from five states since March 1, 2010.

The number of ill persons identified in each state with this strain is: MI (11 confirmed and 2 probable), NY (5 confirmed and 2 probable), OH (8 confirmed and 3 probable), PA (1 confirmed), and TN (1 confirmed).

The reported cases in Tennessee and Pennsylvania do not reflect expansion of the outbreak, according to CDC, but retrospective identification of cases using the PulseNet system indicates that these cases are part of the original cluster due to the original implicated lot of lettuce from March.

Among the 30 patients with available information, 12 (40 percent) were hospitalized. Three patients have developed a type of kidney failure known as hemolytic uremic syndrome, or HUS.

No deaths have been reported.

The bacteria responsible for this outbreak–STECs–have been associated with human illness, including bloody diarrhea and HUS. STEC bacteria are grouped by serogroups (e.g., O157 or O145).

The STEC serogroup found most commonly in U.S. patients is E. coli O157. Other E. coli serogroups in the STEC group, including O145, are sometimes called “non-O157 STECs.” Currently, there are limited public health surveillance data on the occurrence of non-O157 STECs, including E. coli O145; therefore, E. coli O145 may go unreported. Because it is more difficult to identify than E. coli O157, many clinical laboratories do not test for non-O157 STEC infection.

Investigators are using pulsed-field gel electrophoresis (PFGE), a type of DNA fingerprint analysis of E. coli bacteria obtained through diagnostic testing to identify cases of illness that might be part of this outbreak. This testing is done in public health laboratories as part of the PulseNet network. Investigators have established a common definition of confirmed and probable cases related to this outbreak.

Confirmed cases, according to CDC,  are persons with:

-Shiga toxin-producing E. coli O145 infection, or Shiga toxin-producing E. coli infection with O Group pending, AND

-an illness onset on or after March 1, 2010, AND

-a DNA fingerprint matching the outbreak strain; AND

-an epidemiologic link to the outbreak.

Probable cases are persons with a strong epidemiologic link to the outbreak and

-Shiga toxin-producing E. coli O145 infection with an illness onset on or after March 1, 2010 regardless of DNA fingerprint pattern, AND/OR

-hemolytic uremic syndrome; AND/OR

-a laboratory specimen with evidence of  Shiga toxin 2 [stx2] or Shiga toxin, but toxin type is unknown or pending.

CDC also concluded that:

-Multiple lines of evidence have implicated shredded romaine lettuce from one processing facility as a source of infection in this outbreak. This evidence includes the identification of the outbreak strain of E. coli O145 from an unopened package of shredded romaine lettuce obtained at an institution that received product from the processing facility linked to the outbreak.

-Case-control studies in Michigan and Ohio found significant associations between illness and consumption of romaine lettuce processed at the same facility that processed lettuce consumed by ill persons in New York, Pennsylvania, and Tennessee.

-The lettuce-processing company has issued a recall of lettuce produced at its facility as a result of the evidence obtained to date.  An additional recall was issued by a separate company that received lettuce from the same farm as the processing company linked to the outbreak.

Testing of shredded romaine lettuce from the processing company also identified an E. coli O143-producing Shiga toxin 1, which is different from the outbreak strain.  This strain is not associated with any human illness, and appears to be an incidental finding.   

CDC said the investigation is ongoing. At this time, local, state, and federal health officials are involved in many different types of investigative activities, including:

-Conducting surveillance for additional illnesses that could be related to the outbreak.

-Conducting epidemiologic studies that includes gathering detailed information from ill persons (cases) and from healthy persons (controls) about foods recently eaten and other exposures.

-Gathering and testing food products that are suspected as possible sources of infection to see if they are contaminated with bacteria.

-Following any epidemiologic leads gathered from interviews with patients, food purchase information, or from patterns of processing, production and/or distribution of suspected products.

-FDA is working closely with its state partners in the investigations at the food processor and at the farm level to determine where in the distribution chain the point of contamination likely occurred.

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