Four illnesses that are part of an E. coli outbreak in France linked to cheese made with unpasteurized, raw milk could have been caused by cross contamination, according to researchers.

From March 25 to April 27, there were 19 suspected Shiga toxin-producing E. coli (STEC) associated pediatric hemolytic uremic syndrome (HUS) cases were reported by hospitals to Santé publique France, compared with five to 10 cases during the same period in previous years. Thirteen patients were confirmed as being infected from serogroup O26 with whole genome sequencing (WGS) underway for strain comparison.

Investigations identified 16 outbreak patients including 14 pediatric HUS cases, as well as a 63-year-old adult and one child with diarrhea.

Raw cow’s milk soft cheeses of the brands Saint-Félicien and Saint-Marcellin made by Fromagerie Alpine were identified as the probable source of the infections but no positive STEC O26 cheese or milk samples have yet been identified.

Cross contamination investigation
Four outbreak cases did not consume the unpasteurized cheeses, but a household member had, according to the study published in the journal Eurosurveillance.

Researchers said this suggests affected children may have been infected via cross contamination by knives, cutting boards or hands.

None of the household members reported symptoms of illness indicating the outbreak patients were unlikely to have been infected by person-to-person transmission.

Investigations are ongoing to further document exposures of the patients such as consumption of cheeses or other food items cut by the knives or on the same cutting boards as the implicated cheeses.

“In the current outbreak, several families reported consumption of the suspected cheeses by family members, but not by the ill child. This suggests that the risk of cross contamination from food vehicles consumed by family members of young children should also be considered during investigations,” said researchers.

All HUS cases needed hospital treatment
The 16 outbreak victims live in six regions of France. All pediatric cases are younger than five years of age; the median is 22 months with an age range of 6 months to 63 years. Eight cases are female and date of symptom onset was between March 31 and April 29.

All of those who developed HUS were hospitalized. Thirteen of the outbreak patients received blood and/or platelet transfusions and seven underwent dialysis. Six patients had neurological complications, all of them received transfusions and three also had to have dialysis.

Researchers said the outbreak is notable for the young age of cases and severity of illness.

“While pediatric HUS cases are likely to be notified to public health authorities through the national surveillance system, STEC infections presenting as non-complicated diarrhea may not be identified and the number of cases linked to this outbreak may be underestimated,” according to the research report.

Initial epidemiological investigations using a trawling questionnaire identified consumption of raw cow’s milk cheese of the brands Saint-Félicien and Saint-Marcellin as the common link for eight of 13 cases.

Traceback investigations using supermarket loyalty cards identified Fromagerie Alpine as a common producer of these cheeses. A recall was initiated by health authorities in late April and expanded in early May. All cheeses from the producer made from Feb. 1 to April 27 this year were recalled from supermarkets and other retail shops.

In France, STEC monitoring is based on surveillance of HUS in children aged less than 15 years by a network of voluntary pediatric and pediatric nephrology departments.

Since April 2017, isolated strains have been sent to the French National Reference Centre for E. coli, Shigella and Salmonella (NRC-ESS) at the Pasteur Institute for whole genome sequencing and to see if they belong to a cluster.

Of all human isolates received at the NRC-ESS from 2016 to April 2019, only one belonged to the same cluster. SNP analysis revealed this isolate was a close ancestor to the current 2019 outbreak isolates. The strain was isolated in September 2018, from a pediatric HUS patient living in a region near Fromagerie Alpine. Investigations did not identify a link with current outbreak patients.

Information was sent to international health authorities through the European Centre for Disease Prevention and Control (ECDC). As of May 27, none of the 13 responding countries have reported cases linked to the outbreak. Thirty-three countries received the incriminated products.

By Joe Whitworth