The CDC has declared a deadly E. coli O157:H7 outbreak over, but the cause remains a mystery.

The outbreak, which began in mid-December 2020, continued to make people sick through at least Jan. 12 this year. One person died, according to an outbreak update posted this afternoon by the Centers for Disease Control and Prevention.

Samples from more than half of the patients had antibiotic-resistant infections. Whole genome sequencing (WGS) showed all of the patients had closely related strains of the E. Coli O157:H7. This means that people in this outbreak likely got sick from eating the same food, according to the CDC. A number of the outbreak patients reported eating romaine lettuce before becoming ill.

“WGS also showed that this outbreak strain was previously linked to various sources, including romaine lettuce and recreational water,” the CDC reported. “FDA conducted traceback investigations on several produce items but did not identify a common source or potential point of contamination.”

As of the release of the CDC update, the Food and Drug Administration had not updated its specific outbreak investigation page. However, the CDC reported its investigation has ended.

A total of 22 people across seven states were confirmed as outbreak patients. The particularly severe illnesses in this outbreak required that half, 11, of the patients receive in-patient treatment at hospitals. 

Illnesses started on dates ranging from Dec. 18, 2020, to Jan. 12 this year.

Sick people ranged in age from 10 to 95 years old, with a median age of 28. Of 20 people with information available, 11 were hospitalized. Of 18 people with information, three developed a type of kidney failure called hemolytic uremic syndrome (HUS). One death was reported from Washington.

This outbreak was one of three detected in 2020 that did not have a specific source identified. One outbreak was linked to leafy greens in general, with some connection to romaine, but nothing definitive, according to the CDC and FDA. Romaine was mentioned as one of several possible sources in the other outbreak. 

No recalls were initiated in relation to any of the three outbreaks.

The first outbreak, linked to leafy greens, sickened 40 people across 19 states with 20 requiring hospitalization. No one died.

In the second outbreak, cause not definitively known, one person died and a total of 32 people across 12 states were sickened. Fifteen of the patients required hospitalization.

About E. coli infections
Anyone who has developed symptoms of E. coli infection should seek medical attention and tell their doctor about their possible exposure to the bacteria. Specific tests are required to diagnose the infections, which can mimic other illnesses.

The symptoms of E. coli infections vary for each person but often include severe stomach cramps and diarrhea, which are often bloody. Some patients may also have a fever. Most patients recover within five to seven days. Others can develop severe or life-threatening symptoms and complications, according to the Centers for Disease Control and Prevention (CDC).

About 5 to 10 percent of those diagnosed with E. coli infections develop a potentially life-threatening kidney failure 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.

Many people with HUS recover within a few weeks, but some suffer permanent injuries or death. This condition can occur among people of any age but is most common in children younger than five years old because of their immature immune systems, older adults because of deteriorating immune systems, and people with compromised immune systems such as cancer patients.

People who experience HUS symptoms should immediately seek emergency medical care. People with HUS will likely be hospitalized because the condition can cause other serious and ongoing problems such as hypertension, chronic kidney disease, brain damage, and neurologic problems.

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