E. coli can be found living in the intestines of both people and animals, as well as in food and in the environment. Almost all strains of E. coli are harmless, but some can cause stomach cramps, diarrhea and vomiting.
Healthy adults usually recover from an infection of E. coli within a week, but some strains can cause more severe illness, especially in young children and older adults, who are at greater risk of developing kidney failure.
"Leafy greens, such as lettuce, can become contaminated in the field by soil, contaminated water, animals or improperly composted manure," said Jeff Farber, director of the Canadian Research Institute for Food Safety and a professor at University of Guelph in Ontario. "Lettuce can also be contaminated by bacteria during and after harvest from handling, storing and transporting the produce."
Usually, people eat romaine lettuce without cooking it, which could kill the germs. "Other raw fruits and vegetables that have come into contact with feces from infected animals are another common source of infection," Farber said.iPhone transfer software
Popularity also plays a role in why lettuce is a frequent bad actor: "Lettuce is also eaten the most out of all the produce items," he said.
Many modes of contamination
In the current outbreak, 52 of the 102 patients who have been interviewed by public health officials have been hospitalized, including 14 who developed a type of kidney failure called hemolytic uremic syndrome. This 51% hospitalization rate is higher than the 30% typically seen in E. coli outbreaks.
The strain of bacteria involved in the outbreak is Shiga toxin-producing Escherichia coli O157:H7. This "tends to cause more severe illness, which may explain why there is a high hospitalization rate," the CDC said in its outbreak investigation update.
Between 1998 and 2016, there were 45 outbreaks associated with Shiga toxin-producing E. coli in leafy vegetables reported in the United States, CDC spokeswoman Brittany Behm said. The new one is the largest outbreak of its kind since a deadly E. coli outbreak in 2006 that was linked to spinach.
In the new outbreak, the investigation revealed that several people in an Alaska correctional facility who became sick had consumed romaine lettuce sourced from Harrison Farms of Yuma, Arizona. The agency has not determined where in the supply chain contamination occurred.
"Lettuce can be contaminated in many different ways from the farm through the distribution chain," Behm said. "It could be from manure in the fields to contaminated water to contamination within a processing facility."
"Any commercially grown lettuce product will be put through some basic wash step before it's sold," Noble explained. The series of baths and tumblers is not a thorough cleaning, however; it's just enough that the end product is "appealing to the customer."
She added that, although commercial producers do some testing for E. coli on wash water and irrigation water, not every single product that makes it into the hands of a customer is tested.
'A very safe food supply' overall
The E. coli testing is based on the Food Safety Modernization Act, a set of regulations enacted in August 2015 that requires growers with a certain size farm to sample water associated with produce, Noble said.
"The goal was to set up a monitoring scheme to protect the public," she said. The regulations are still being phased in, so some growers have begun monitoring programs but others have not.
Though these monitoring programs measure the total volume of E. coli in the water, it might not take a high number of bacteria to make someone sick, since the Shiga toxin-producing strains can be potent, Noble said.
All told, Farber believes, "both the US and Canada have a very safe food supply."
Still, consumers have "a role to play," he said, by paying attention to food recalls and asking questions when they are unsure of quality or safety of a food product. They also need to know "that 'best before' or 'use by' dates are only based on quality and not safety."
With the growing season in the Yuma region at an end, Harrison Farms and others in the region are not growing any lettuce now, but the CDC still warns consumers against eating romaine lettuce at this time unless it isn't from the region.
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Generally, Farber recommends washing your hands thoroughly with warm water and soap for at least 20 seconds before and after handling lettuce and then washing lettuce thoroughly under fresh, cool running water. Wilted or brown leaves should be discarded along with the outer lettuce layer, he said.
"There is no need to use anything other