This article by Coral Beach first appeared in Food Safety News and is reposted here with permission.

Federal officials say contaminated canal water near romaine lettuce growing fields is the likely source of the unusually virulent strain of E. coli that has sickened people across 36 states, killing five.

The outbreak is over, according to an update this afternoon from the Centers for Disease Control and Prevention. The agency has confirmed 210 people with infections. Twenty-seven of the victims have developed kidney failure. The most recent victim became sick on June 6.

“Samples have been collected from environmental sources in the region, including water, soil, and cow manure. Evaluation of these samples is ongoing,” according to an update this afternoon from the Food and Drug Administration investigators.

“To date, CDC analysis of samples taken from canal water in the region has identified the presence of E. coli O157: H7 with the same genetic fingerprint as the outbreak strain. We have identified additional strains of Shiga-toxin producing E. coli in water and soil samples, but at this time, the samples from the canal water are the only matches to the outbreak strain.”

Growers, researchers and produce trade associations have said in recent weeks that the Yuma area uses canal water from the Colorado River for irrigation and other agriculture uses. Some have theorized that a common water source is one of the most likely sources of the E. coli bacteria.

“CDC laboratory testing identified the outbreak strain of E. coli O157: H7 in canal water samples taken from the Yuma (AZ) growing region,” according to the CDC’s update this afternoon, which is the first since June 1.

“The U.S. Food and Drug Administration is continuing to investigate the outbreak to learn more about how the E. coli bacteria could have entered the water and ways this water could have contaminated romaine lettuce.”

FDA last reported to the public on June 1 when traceback efforts were still stymied because of a tangle of hand-written, incomplete and incompatible shipping and receiving records through the supply chain from growers to retailers.

From the beginning of the outbreak, FDA and CDC have said the implicated romaine lettuce came from the Yuma growing region. Produce industry individuals and groups told the federal agencies the last romaine from that area was harvested April 16. People usually begin to show symptoms of infection in less than a week after exposure to E. coli bacteria.

The first confirmed illness in the outbreak began on March 13. The age range of victims is 1 to 86 years old.

“In interviews, ill people answered questions about the foods they ate and other exposures they had before they became ill. Of the 166 people interviewed, 145 (87 percent) reported eating romaine lettuce in the week before their illness started,” according to the CDC.

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A Supplementary Note

In a related Food Safety News opinion piece, Coral Beach highlights the long delay between the determination of the geographic source of the E. coli O157:H7 outbreak and the sampling of canal water in the region.

In Chapter 8 of my book, Food Safety: Old Habits, New Perspectives, published in 2007 by ASM Press, I wrote:

Take a drive on the Interstate 5 through California’s San Joaquin Valley and you will pass fields of produce, open irrigation canals, and cattle feedlots. Irrigation is a way of life in this semi-arid agricultural area; rain is a rare visitor, except during the winter months. But when it rains, it pours. The soil becomes saturated, and excess water drains off the fields and feedlots. Some of the runoff finds its way into the irrigation canals, bringing with it pathogens such as E. coli O157:H7.

This observation is equally applicable to the agricultural region around Yuma, Arizona.