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Local, state and federal investigators are scratching their heads and hoping for a break as they try to identify the source of an outbreak of E. coli O157:H7 that has sickened at least 26 people in and around St. Louis, Missouri since October 25th. At least 19 outbreak victims have been hospitalized.

According to the Washington Post, the outbreak victims range in age from 1 to 94, and live in St. Louis city and four surrounding counties – St. Louis, Jefferson and St. Charles counties in Missouri, and St. Clair county in Illinois. The Illinois Department of Public Health acknowledged on October 28th that it was investigating a single illness in St. Clair County that might be linked to the Missouri outbreak.

The Missouri Department of Health and Senior Services is testing samples from an additional 25 suspect cases as part of the investigation into the outbreak, which appears to be linked to food sold from supermarket salad bars. At least some of the suspect salad bar components were supplied by distributors or processors outside of the state of Missouri, and FDA has been called in to assist in the inspection of the individual links in the distribution chain.

Initial patient interviews appeared to point to Schnucks Markets, Inc. salad bars as a common link. Schnucks is a regional supermarket chain headquartered in St. Louis, with Schnucks stores located in Missouri, Illinois, Indiana, and Iowa, and Logli/Hilander stores located in Rockford, Illinois and Janesville, Wisconsin.

Based on the initial information obtained from patients, Schnucks removed certain items from all of its salad bars, and replaced the items with products obtained from other suppliers. None of the items sampled so far from Schnucks salad bars or from the homes of patients have yielded E. coli.

After an additional round of patient interviews, a further 38 food samples have been collected from five Schnucks stores and submitted to the State lab for testing. These new samples include Bistro Salad Dressing, broccoli florets, deviled eggs, diced hard-boiled eggs, honey Dijon dressing, Italian dressing, pineapple chunks, red wine vinaigrette, shredded carrots, shredded radishes, shredded zucchini, and sliced red onions. In addition, six packaged salads that contain salad bar ingredients were submitted for analysis: Bistro Chopped Salad, Fresco House Salad, Fried Chicken Salad, Garden Salad, Italian Salad, and Turkey Cobb Salad.

The U.S. Centers for Disease Control and Prevention (CDC) has been called upon to assist in the epidemiological investigation, and is carrying out a case control study. The study will compare foods eaten by confirmed outbreak patients with foods consumed by a control group of healthy individuals living in the same area. With judicious questioning – and with some luck – the case control study might be successful in identifying one or more probable food sources for the outbreak.

Salad bar-related outbreaks can be especially difficult to trace to a source, due to the sheer number of different items present, and the potential for cross-contamination from serving utensils or the dropping of one salad bar item into another. Small salad ingredients, such as sliced vegetables, cherry tomatoes, and sprouts are especially susceptible to landing in the wrong bin. And people often don’t remember every vegetable or garnish that they selected.

Another complication in this outbreak investigation is the short shelf life of salad ingredients. The contaminated component may no longer be in the distribution chain. The longer it takes for a possible food to be identified via patient interviews and the case control study, the less likely it becomes that the contaminated food will be identified.

The State has not provided any time-related breakdown of the reported cases, so it’s difficult to tell whether or not the outbreak has reached its peak. Consumers in the St. Louis metropolitan area and surrounding counties should be especially careful in purchasing and handling salad items while this outbreak continues.

Public health officials in Missouri are urging anyone experiencing gastrointestinal symptoms, such as severe stomach cramps, diarrhea or nausea to seek medical attention.

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