Researchers have detailed the first reported Clostridium perfringens outbreak in England associated with leeks in leftover and reheated cheese sauce.

In December 2018, public health authorities were alerted to 34 reports of diarrhea with abdominal cramps from diners who ate Christmas meals at a restaurant in Bridgnorth, the West Midlands.

Eight people reported illness to the Food Standards Agency or Shropshire Council on behalf of their dining group after they became unwell following eating at the restaurant. Two fecal samples were positive for Clostridium perfringens with one confirming the enterotoxigenic gene.

Improvisations in the kitchen to deal with increased customer throughput over Christmas, such as use of leftovers, overnight cooking and factors like a lack of food preparation protocols for staff may have contributed to the outbreak, according to the study published in the journal Epidemiology and Infection.

Following removal of leeks in cheese sauce from the menu and changes to food preparation and temperature control in the kitchen and serving areas, no further cases were reported.

Third time lucky
The outbreak investigation had a primary hypothesis of norovirus, due to a staff member with suspected gastroenteritis, rapid onset of illness and poor food practices seen at the first site visit. This meant a decision was made not to do food sampling. The second hypothesis suspected Clostridium perfringens but focused environmental investigations on meat and gravy preparation.

Researchers recommended keeping an open mind during initial investigations and always doing food and environmental sampling at the first opportunity in suspected food-related outbreaks.

Shropshire Council Environmental Health Practitioners visited the site four times during the investigation. Eight food samples were taken but none were during the exposure period.

Cooked turkey, beef and pork and cauliflower and leeks in cheese sauce and gravy tested negative for pathogens. Indicator organism counts on cauliflower cheese showed an unsatisfactory aerobic colony count of more than 105 colony forming units per gram according to ready-to-eat guidelines.

Environmental investigations identified likely cross-contamination between raw and cooked foods and reuse of leftover cheese sauce for the next day’s service. Food preparation methods for leeks in cheese sauce included reuse of leftover sauce combined with ambient cooling; microwave reheating and inadequate hot-holding temperatures. Preparation for cauliflower cheese differed so this dish with the sauce was kept under temperature control.

The first visit highlighted lapses in standard food hygiene and temperature control during cooking, hot holding and serving. A member of bar staff was working whilst symptomatic and a person was allegedly sick on the premises the day before the first reported exposure. The food hygiene history of the restaurant consistently maintained a rating of 5 out of 5 during the past seven years.

Link to leeks in cheese sauce
Of the 102 reported diners who had eaten at the restaurant, 44 had no symptoms whereas 58 were unwell. A total of 43 people responded to the questionnaire. Three did not meet the case definitions, as they did not eat at the restaurant, and were removed from the analysis.

Of the rest, 28 were cases and 12 were controls. The median age of respondents was 65 years with a range of 5 to 86 years old. Sixty-three percent of cases were female.

One group of five diners ate at the dinner service prepared during the day; the other 97 ate at lunch prepared overnight. Shropshire Council was made aware of four more cases among staff at the restaurant but they were excluded as food exposures or exposure dates could not be established.

Of the 28 cases, 27 experienced diarrhea and abdominal pain and four reported vomiting. One person needed hospital treatment. The median incubation period was 17 hours with a range of less than one hour to three days. Half of the cases reported symptoms lasting less than 24 hours, and 79 percent had symptoms lasting 48 hours or less.

Four food exposures were of interest from an analysis, leeks in cheese sauce, mashed swede, stuffing and cauliflower cheese. The odds of becoming ill were 50 times higher in those who ate leeks in cheese sauce compared to those who did not consume the dish.

Researchers said the outbreak is as a reminder to businesses to ensure that staff training is updated when food items are added or changed on the menu especially when cooking processes change. When using digital temperature recording systems, firms should ensure multiple trained users have access and all user-definable parameters are correctly set up for temperature critical control points and corrective limits.

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