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  1. Outbreaks of Foodborne Illness

FDA Ends Investigation of E. coli O157:H7 Outbreak Likely Linked to Leafy Greens


February 28, 2018

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The U.S. Food and Drug Administration, along with the Centers for Disease Control and Prevention (CDC) and state and local partners, investigated an outbreak of E. coli O157:H7 illnesses that were likely linked to leafy greens.

Fast Facts

  • The FDA has ended an extensive traceback investigation of an outbreak of E. coli O157:H7 illnesses that were likely linked to leafy greens after exhausting all leads.
  • The 25 illnesses occurred in the time period of November 5 to December 12, 2017. The FDA learned of this outbreak on December 12, 2017, the same day as the last illness onset.
  • Although CDC announced on January 25, 2018 that the outbreak appeared to be over, the FDA’s outbreak investigation team continued to work with federal, state, and local partners to determine what leafy greens people ate (potentially making them ill), where they bought it, and to identify the distribution chain -- all with the goal of identifying any common food or points where the food might have become contaminated.
  • The FDA’s traceback investigations focused on romaine lettuce due to the genetic relatedness of the U.S. illness to Canadian cases that were associated with romaine lettuce. Both U.S. and Canadian investigations did not identify a common supplier, distributor or retailer for romaine lettuce identified by people who became sick.

What was the Problem and What is being Done About It?

The FDA and the CDC, along with state and local health officials, investigated an outbreak of Shiga toxin-producing E. coli O157:H7 infections likely linked to leafy greens. There were 25 cases in 15 states; California (4), Connecticut (2), Illinois (1), Indiana (2), Maryland (3), Michigan (1), Nebraska (1), New Hampshire (2), New Jersey (1), New York (2), Ohio (1), Pennsylvania (2), Vermont (1), Virginia (1), and Washington (1).

Illness onsets were between November 5 and December 12, 2017. Of the 25 illnesses CDC linked with this outbreak, CDC was able to gather detailed information on 21 of them. Among these 21 people, nine were hospitalized and one person died. Two people developed hemolytic uremic syndrome, a type of kidney failure known to be a complication of E. coli O157:H7 infections.

The FDA was made aware of this outbreak from CDC on December 12, 2017. The agency also learned from CDC that the bacterial strain isolated from ill persons in the U.S. was genetically similar to a strain of E. coli O157 causing an outbreak in Canada during the same time period as the U.S. illnesses. On December 11, 2017, the Public Health Agency of Canada announced their outbreak was linked to romaine lettuce.

Since learning of  the outbreak, the FDA worked closely with CDC and state and local partners on the investigation, as well as with Canadian food safety authorities. The FDA’s role in outbreaks of this nature is to utilize food consumption information gained from interviews with people who got sick, trace those foods back through the distribution chain, and attempt to identify the source and route of contamination.  

In this particular outbreak investigation, ill people reported consuming several different leafy greens. The FDA focused on tracing back the sources of romaine lettuce for several cases in this cluster because of the genetic relatedness of the E. coli O157 isolates to those from Canadian cases to determine if the U.S. and Canadian cases had common sources of romaine lettuce.  The FDA determined that romaine lettuce that ill persons may have eaten at the time of exposure was likely supplied by multiple firms located in Arizona, California, and Mexico, which are also the geographic locations of most romaine lettuce marketed in the U.S. and Canada. 

In a typical traceback effort, the FDA identifies clusters of people made ill, especially in different geographical regions and works to trace the food eaten by those made ill to a common source. In situations where there is no packaging available for the reported or suspect product that may help conduct a traceback, FDA scientists and investigators work with partners and companies to collect, review and analyze hundreds--sometimes thousands--of invoices and shipping documents. This process is labor-intensive, but also dependent on the quality of records. In this outbreak, due to the absence of geographically distinct clusters of illnesses, absence of original packaging from ill persons, and large number of potential suppliers, no common source could be identified after exhausting all available leads. 

While the Public Health Agency of Canada identified romaine lettuce as the source of their outbreak, the U.S., epidemiologic investigations suggested leafy greens as the likely source of illnesses, but could not identify a specific type of leafy green as the cause, which made traceback investigations more challenging.

The FDA was in regular contact with Canadian health authorities to share information to facilitate our traceback investigation. The FDA’s investigation team also reviewed information from previous outbreaks to see if there are any commonalities between those and the current outbreak. No common leafy green grower source, supplier, or retailer was identified.

Learn more:

What are the Symptoms of E. coli O157:H7 Infection?

The symptoms of Shiga toxin-producing (STEC) E. coli infections vary for each person but often include severe stomach cramps and bloody diarrhea. If there is fever, it is usually not very high (less than 101 degrees Fahrenheit/less than 38.5 degrees Celsius). Most people get better within 5–7 days. Some infections are very mild, but others are severe or even life-threatening.

Around 5–10 percent of those who are diagnosed with STEC infection develop a potentially life-threatening complication, known as hemolytic uremic syndrome (HUS).

Symptoms of HUS include fever, abdominal pain, feeling very tired, decreased frequency of urination, small unexplained bruises or bleeding, and pallor. Most people with HUS recover within a few weeks, but some suffer permanent damage or die. People who experience these symptoms should seek emergency medical care immediately. Persons with HUS should be hospitalized because their kidneys may stop working (acute renal failure), but they may also develop other serious problems such as hypertension, chronic kidney disease, and neurologic problems.

Learn more:

Who is at Risk?

Although this outbreak appears to be over, it’s important to know that people of any age can become infected with Shiga toxin-producing (STEC) E. coli. Children under the age of 5 years, adults older than 65, and people with weakened immune systems are more likely than others to develop severe illness, including HUS, but even healthy older children and young adults can become seriously ill.

What Do Restaurants and Retailers Need To Do?

Retailers, restaurants, and other food service operators should always take steps to avoid the cross contamination of cutting surfaces and utensils through contact with potentially contaminated products. Retailers, restaurants, and other food service operators should always take steps to adequately control the temperature of cut leafy greens and to avoid cross contamination of cutting surfaces and utensils through contact with potentially contaminated products. To prevent cross contamination, you should follow the steps below:

  • Wash and sanitize display cases and refrigerators where potentially contaminated products were stored.
  • Wash and sanitize cutting boards, surfaces, and utensils used to prepare, serve, or store potentially contaminated products.
  • Wash hands with hot water and soap following the cleaning and sanitation process.
  • In accordance with the FDA Food Code 2017, cut leafy greens are considered a food requiring time/temperature control for safety and should be refrigerated at 41°F or lower.

Regular frequent cleaning and sanitizing of food contact surfaces and utensils used in food preparation may help to minimize the likelihood of cross-contamination.

What Do Consumers Need To Do?

Consumers should always practice safe food handling and preparation measures. It is recommended that they wash hands, utensils, and surfaces with hot, soapy water before and after handling food.

For refrigerators and other food preparation surfaces and food cutting utensils that may have come in contact with contaminated foods, it is very important that the consumers thoroughly clean these areas and items.

Consumers should follow these simple steps:

  • Wash the inside walls and shelves of the refrigerator, cutting boards and countertops; then sanitize them with a solution of one tablespoon of chlorine bleach to one gallon of hot water; dry with a clean cloth or paper towel that has not been previously used. 
  • Wash hands with warm water and soap for at least 20 seconds before and after handling food.
  • Wipe up spills in the refrigerator immediately and clean the refrigerator regularly.
  • Always wash hands with hot, soapy water following the cleaning and sanitization process. 
  • Persons who think they might have become ill from eating potentially contaminated foods should consult their health care provider.

Who to Contact

Consumers who have symptoms should contact their health care provider to report their symptoms and receive care.

To report a complaint or adverse event (illness or serious allergic reaction), you can

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