Unusual E coli strain sickens 231 in Oklahoma

Sep 10, 2008 (CIDRAP News) – A restaurant-related illness outbreak in Oklahoma featuring an uncommon strain of Escherichia coli has expanded to involve at least 231 people, 61 of whom have been hospitalized, Oklahoma health officials announced today.

The sick have been infected with E coli O111, a far less common strain than E coli O157:H7, the serotype typically identified in E coli outbreaks. Both strains can cause the form of kidney failure known as hemolytic uremic syndrome (HUS), which is potentially fatal.

Sixteen of the 61 people hospitalized in the outbreak have received dialysis treatment, including nine children, the Oklahoma State Department of Health (OSDH) said in an update today. The patients include 185 adults and 43 children; three patients' ages have not yet been learned, officials said.

"We still have some individuals who are on dialysis for HUS," Oklahoma State Epidemiologist Dr. Kristy Bradley told CIDRAP News today. She said there has been one death in the outbreak, that of a 26-year-old man.

The numbers of patients and hospitalizations are likely to change as the investigation continues, the OSDH said today.

Food source elusive
Most case-patients ate at the Country Cottage restaurant in the northeastern Oklahoma town of Locust Grove between Aug 15 and 17, the OSDH has said. But despite interviewing more than 1,300 people who ate there, health officials have not yet identified a specific food source for the outbreak.

"I'd love to say we're zeroing in on a food item, but we've not been able to do that," Bradley said. "We hope that by increasing the number of controls [interviewed], we might have a particular food item or category that will fall out in our analysis, but as our investigation has progressed I'm becoming less and less optimistic. If we're not able to, it points to the possibility that we have an infected food handler who handled multiple food items."

She said that possibility seems more likely, since the restaurant is a large buffet-style operation, with 58 employees who handle food. While most employees have a primary duty station, it is not unusual for them to fill in at other stations as needed, so they would handle a number of foods, she said.

Bradley said investigators have been trying especially to find and interview children who ate at the restaurant during the period in question. Not only are children at greater risk for serious illness, but information from children might equip investigators with valuable clues about possibly contaminated food items.

"Children tend to select fewer things off a buffet than adults," Bradley explained. "We were hoping we might find it [a contaminated food] in a subset analysis of children."

Yesterday officials said testing of surfaces in the restaurant had revealed no contamination, and last week authorities determined that water from a well on the restaurant site was safe.

Largest outbreak of E coli O111
"This appears to be the largest E coli O111 outbreak ever reported in the US," Bradley said in a Sep 2 update on the outbreak.

The first OSDH announcement of the outbreak came on Aug 25. Four days later state officials said the US Centers for Disease Control and Prevention (CDC) had identified the pathogen as E coli O111.

As described by the OSDH, signs and symptoms of the illness have been similar to those of E coli O157:H7: diarrhea or bloody diarrhea, vomiting, and severe abdominal cramps, usually with no or only mild fever. Bradley called the illness "very similar to [those caused by] other enterohemorrhagic E coli strains."

Most of the people infected have had diarrhea lasting a couple of days, but were not sick enough to need medical attention, Bradley said.

How common?
Little is known about the incidence of pathogenic E coli strains (known as Shiga toxin–producing E coli, or STEC) other than O157:H7, according to a January 2007 report by the CDC. Another CDC report, covering FoodNet foodborne disease surveillance in 2006, said the program colleted data on 209 non-O157 STEC isolates, of which 29 (15%) were O111. O26 and O53 strains were more common. (FoodNet surveillance covered about 15% of the US population in 2006.)

The January 2007 CDC report, discussing STEC cases in Connecticut from 2000 to 2005, said, "Overall, infections caused by non-O157 STEC were less severe than those caused by STEC O157. However, the severity of disease caused by STEC is related to the virulence profile of the infecting strain, and some non-O157 serotypes cause illness as severe as that caused by STEC O157."

See also:

OSDH page with links to daily outbreak updates

Sep 10 OSDH news release

January 2007 CDC report on STEC in Connecticut
http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5602a2.htm

CDC report on FoodNet data for 2006
http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5614a4.htm

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