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The CDC reports three more states and 23 more sick people have been confirmed in the past week in its ongoing investigation into an E. coli outbreak associated with romaine lettuce.

As of this week officials have confirmed 172 people across 32 states in the outbreak. One person in California died. Public health officials in Canada have confirmed people in multiple provinces, who reported eating romaine, with infections from the outbreak strain of E. coli O157:H7.

Additional U.S. cases are expected as federal and state officials continue to search for the source of the bacteria. Their focus continues to be on romaine lettuce grown in the Yuma, AZ, area. However, for the first time since April 13, warnings urging consumers to avoid romaine from that area were not included in updates from the Centers for Disease Control and Prevention and the Food and Drug Administration.

The FDA reported Wednesday that produce industry groups have assured officials the last day romaine was harvested in the Yuma area was April 16. Processing, packaging and shipping would have continued for several more days. The FDA update said it is unlikely that romaine from Yuma is still available in stores or restaurants, citing it’s 21-day shelf life. However, the CDC anticipates more people to be confirmed as outbreak victims.

“The most recent illnesses reported to CDC started when romaine lettuce from the Yuma growing region was likely still available in stores, restaurants, and in peoples’ homes,” the agency reported Wednesday. Illnesses that occurred after April 21 might not yet be reported due to the time it takes between when a person becomes ill with E. coli and when the illness is reported.

The outbreak has an unusually high hospitalization rate. Of the 157 victims for whom complete information is available, 75 of them, or 48 percent, have been admitted to hospitals. At least 20 people have developed hemolytic uremic syndrome, a type of kidney failure. 

Elusive source
Outbreak investigators continue to report the illnesses “cannot be explained by a single grower, harvester, processor or distributor,” according to the FDA update. Multiple supply channels are complicating the investigation. Federal and state officials are examining all possibilities, including that contamination may have occurred at any point in the supply chain before reaching consumers at restaurants and grocery stores. 

“… we have found that a single production lot may contain romaine from multiple ranches, which makes the traceback more challenging,” the FDA reported. “We are working with federal and state partners and companies as quickly as possible to collect, review and analyze hundreds of records in an attempt to traceback the source of the contaminated romaine lettuce.”

In addition to sorting through hundreds of shipping and receiving records from the seed-to-shelf continuum, the FDA has investigators on the ground. They are looking at growing fields and adjacent property, water sources, harvesting practices and processing facilities. 

A microbiologist specializing in fresh produce says he does not envy those investigators. Don Stoeckel is the Midwest regional Extension Service associate for the Produce Safety Alliance out of Cornell University and he’s been working with produce for many years. In particular he’s been researching pathogens, including E. coli, and how they behave in water and water systems.

Stoeckel’s research helps health officials estimate the public health consequences of pathogens as they relate to water used in food production. His laboratory studies have been used to improve the monitoring and forensic attribution of pathogens and other contaminants. 

“It’s all about likelihood,” Stoeckel said. “I have a lot of empathy for the people who try to track something from the hospital bed to the farm.”

One thing that is relatively apparent in this outbreak is that a localized source for the E. coli is probably involved, Stoeckel said, even though FDA investigators have found romaine from multiple growers and processors can be mixed together to create one “lot” of chopped romaine.

Some people have theorized the E. coli contamination was from a common water source, manure dust and debris, or wildlife incursions in fields. Those explanations seem plausible, until a microbiologist weighs in.

Stoeckel said it’s unlikely that surface water is the source because only one strain of E. coli is involved. If the contamination was coming from surface water there would be multiple DNA fingerprints of E. coli showing up.

The same goes for contamination from wildlife and domestic animals’ manure. Multiple strains of E. coli would be most likely be involved, Stoeckel said. As for water used in facilities that wash and chop fresh produce such as romaine, Stoeckel said he didn’t want to second guess industry or government investigators on that topic. 

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