This week saw the E. coli O157:H7 outbreak associated with romaine lettuce expand to include every border state from New York to Washington state.

With 149 people infected in 29 states, it was probably inevitable that Canada also would find itself with a romaine lettuce problem. After all, it does not have a border wall to prevent pathogens from crossing.

To view a larger version of this map, please click on the image.

And romaine lettuce is the likely source of six illnesses in Canada that are genetically similar to those involved in the 29-state outbreak in the U.S. The Canadian sicknesses are also likely linked to romaine lettuce grown in the Yuma, AZ, growing region, according tot public health officials.

Two of the ill Canadians reported traveling to the United States and eating romaine lettuce while visiting. The others ate romaine lettuce at home or in prepared salads purchased at grocery stores, restaurants, and fast food chains before their symptoms began.

If the Canadian market is selling contaminated romaine lettuce, the Canadian Food Inspection Agency (CFIA) will recall the product. Like the U.S. Food and Drug Administration and Centers for Disease Control and Prevention, Canada has not been able to pinpoint a source or brand for the implicated romaine.

The Yuma, AZ, growing area is the suspect, but the  region contains 225,000 acres of irrigated Colorado River land with seven irrigation districts. Often called “the winter salad bowl,” the Yuma area grows billions of dollars worth of iceberg, romaine, spinach and leafy lettuces. Its winter crop is generally harvested from November through the end of March and distributed across the U.S.

Canadians were sickened between late March and mid-April in four provinces — one each from Alberta and British Columbia and two each in Saskatchewan and Ontario. One person in required hospitalization, but all recovered.

The Public Health Agency of Canada has advised Canadians traveling to the U.S. or crossing the border to shop for groceries in the U.S. to follow the advice of the Centers for Disease Control and Prevention when it comes to eating romaine lettuce. The CDC has been recommending since April 13 that consumers and retailers should avoid romaine from the Yuma area. However, like most fresh produce, lettuce rarely has labeling that includes the state where it was grown.

The U.S. border areas of North Dakota and Minnesota were among four states added to the outbreak this week, giving it a broader footprint than the deadly 2006 E. coli O157:H7 outbreak caused by bagged spinach.

The current outbreak is seen as a critical medical event because 64 of the 149 confirmed cases have required hospitalization. One of the victims died, and 17 others are experiencing kidney failure.

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