Health officials take on E.coli

Containing an outbreak of E. coli (Escherichia coli) is not unlike an episode of the popular TV series CSI. It is an intensive and exhaustive process that puts health officials to the test.

Dr. Catherine Whiting, chief medical officer for the North Bay Parry Sound District Health Unit, and her team of investigators found that out first hand following an outbreak traced to a North Bay Harvey's restaurant in early October.

They swung into action employing a process called the Incident Management System (IMS), an emergency preparedness plan, which was adapted to identify, contain, and deal with an infectious communicable disease identified as the E. coli strain 0157:H7.
Like detective work, it is a process of collecting and compiling information to come up with a better understanding of what happened. Whiting called it epidemiological data analysis.

The health unit serves a population of 121,000 within 31 municipalities, including the City of North Bay. The outbreak involved 10 other Ontario health units, one in Quebec and one in British Columbia, resulting in 250 cases, 50 of which have been confirmed as E. coli 0157:H7. Of those, 40 were from Whiting's jurisdiction.

It was the same strain of E. coli that was at the centre of the Walkerton tainted water crisis of 2000, which resulted in the death of seven people and caused thousands of others to become ill. Not all E. coli are pathogenic, but this particular strain, 0157:H7, is enterohemorrhagic, causing bleeding in the intestinal tract.

When infected, the symptoms are severe abdominal cramping and possibly, bloody diarrhea. Most people recover within eight days. However, between 10 and 20 per cent of those experiencing symptoms may develop hemorrhagic colitis (bleeding colon), or haemolytic uremic syndrome, which can lead to kidney failure, said Dr. Garry Ferroni, a professor of microbiology at the Northern Ontario School of Medicine. The most vulnerable include those with compromised immune systems, children under five years of age and the elderly. The general rule of thumb for this kind of infection is to let it run its course.

Surveillance system

The North Bay Parry Sound District Health Unit has a surveillance system that tracks the number and type of reportable diseases. Whiting said they normally get one case of E. coli a year. Anything outside of "that norm" becomes suspicious.

Initially, the scope of the investigation is broad, but it narrows down as more information is acquired. "You want to be inclusive based on what people are telling you," Whiting said.

Finding the source of the outbreak is not always obvious. Besides the people who fall ill, the health unit relies upon the eyes of emergency room doctors and GPs, daycare workers and those employed in long-term care facilities.

All these facilities work within an established baseline of symptoms commonly seen in the course of a day. If the type and quantity of the symptom goes above and beyond the norm, it raises suspicion and is reported to the public health unit. The trigger in the North Bay ER was the number of people experiencing loose and/or bloody stools.
"Under the Health Protection and Promotion Act (HPPA), they don't have to have the confirmed lab report," Whiting explained. "They only have to have a degree of suspicion to report it to us. We didn't get a positive lab report until the next day, but it is important to report a suspicion so the health unit can start investigating."

Once the health unit was notified, staff set about obtaining a case history from every patient suffering similar symptoms.

"With the initial cluster, it wasn't quite clear," Whiting said. "By the next day, we had more cases and information. Then we could make the connection more clearly about a potential location of exposure. By that point, we had the one confirmed case from the lab that it was E. coli 0157:H7."

Incubation period

The incubation period for E. coli can be up to 10 days, although more commonly it is three to five days. From the time people ate the contaminated food to the time they experienced symptoms and sought medical help, a minimum of three to five days had elapsed. This time span made it difficult to isolate a food source, which as of mid-November, remained a mystery.

A general questionnaire was adapted and used to elicit case histories. People's recollection of food eaten presented some challenges.

Once the origin of the food-borne outbreak was pinpointed, Whiting closed down the restaurant and performed a thorough investigation including the analysis of 73 food samples and disposal of all remaining food. Investigators also made inquiries about how the food was prepared and cooked. The premises were sanitized under supervision, and the restaurant's staff were required to provide stool samples and have a letter clearing them to return to work. Food handlers, health-care or daycare-centre workers all had to be medically cleared and symptom-free for 48 hours before resuming work.

The media were notified, with Whiting acting as the spokesperson for interviews with local and national media.

Public health bulletins were distributed to the victims, providing advice on care, protection and how to prevent spreading the illness. Other notifications were sent to physicians, walk-in clinics, emergency rooms and day-care and long-term care facilities.
Provincial public health units were warned, along with the Ministry of Health and Long-Term Care and the Canadian Food Inspection Agency. The Public Health Agency of Canada was also alerted and sent two field epidemiologists for support.

"In these kinds of investigations, you rarely find the positive food (tested for E. coli) due to the time frame between exposure and the cases presenting themselves," Whiting said. "Most of the food will have been gone by then."

Health officials formed a control group (those who ate at the restaurant during the same time frame but didn't get sick) to study those who got sick and those who didn't, and why.

This analysis was being finalized at press time.

The bacteria itself was "fingerprinted" for DNA.

Once the strain of E. coli was determined, a Pulse Field Gel Electrophoresis (PFGE) test was performed, indicating the patterns were similar to other E. coli cases in Ontario and elsewhere. A more sophisticated DNA test called the Multiple Loci VNTR Analysis (MLVA) further isolated the type of bacteria.

"In our situation, the MLVA was very distinctive and not that common in Canada," Whiting said.

In mid-November, the case had not been declared over because they were waiting for results from some secondary cases.

"We must wait until the last possible case and several incubation periods beyond that before we can say it is over," Whiting said. But the North Bay Harvey's restaurant was given the green light to reopen on November 12, after being shut down for four weeks.
Whiting said they also contacted Dr. William Clarke, a nephrologist and lead investigator of the Walkerton Health Study at the University of Western Ontario, in order to inquire about the long-term effects of contamination.

Lawsuit

One of the results of the outbreak was a $17-million class-action lawsuit filed against Harvey's parent company, Cara Operations Ltd., claiming negligence in serving E. coli-contaminated food.

The outbreak will be a memorable send-off for Whiting, who retires at the end of December. However, her successor Dr. Jim Chirico, who was on placement at the health unit during the outbreak, received valuable field experience prior to donning the medical officer's hat.

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