It is probable that the 44 cases with a confirmed link to the food bank represent just a small proportion of the actual number of cases, they said.
The prolonged outbreak of S. Enteritidis from December 2014 to April 2015 involved the first outbreak notification on 30 December 2014 and the second on 2 March 2015.
In France, notification of foodborne disease outbreaks (FBDO) to the regional health agency (ARS) is mandatory for health professionals, clinical microbiologists and institutional catering services.
The ARS is responsible for case investigations while the Departmental Direction for the Protection of Populations (DDPP) does food safety investigations. The ARS then transmits results of outbreak investigations to Santé publique France (SpFrance).
A total of 45 cases were interviewed on food consumption. Twenty-three were confirmed S. Enteritidis, 17 were probable and five were possible cases.
Information on age was known for 37 of 45 cases and ranged from one month to 49 (median age: nine years) with eight children and one adult being hospitalised.
Of the 45 cases with consumption information, 41 had eaten frozen beefburgers from a food bank.
No other countries reported outbreaks of S. Enteritidis linked to frozen beefburgers from the Polish producer.
Epidemiological investigations following initial notification of five cases of salmonellosis (two confirmed S. Enteritidis) in young children in the Somme department revealed all cases went to the same food bank.
A second notification of cases in the Somme reinitiated investigations that confirmed a link with the food bank and consumption of frozen beefburgers from the same Polish producer.
While six departments received frozen beefburgers from the suspected lot, cases were only identified in three of them.
Visits to three sites of the food bank as well as the regional distribution platform for northern France by the DDPP revealed no non-compliance in storage conditions or the cold chain.
Two-thirds of families reporting degree of doneness indicated burgers were consumed medium-rare or rare, said the researchers.
“Although it was not possible to quantify contamination levels, this could indicate that the frozen beefburgers were highly contaminated and that contamination levels may have been greater for the second lot recalled based on the greater number of family FBDOs around incident cases.”
The research was presented at the International Symposium Salmonella and Salmonellosis (I3S) in Saint Malo, France this year.
Recall and food testing
In January 2015, the food bank temporarily blocked distribution of all lots of frozen beefburgers after a common lot from a producer in Poland was identified linked to illnesses.
No food samples were available for testing but trace-back investigations revealed two samples from the lot tested positive in August 2014 for Salmonella spp. by the Polish producer.
After removal of the concerned part, a second series of samples in September 2014 tested negative and the lot was sent by the producer to France for distribution.
Epidemiological investigations demonstrated that several cases identified after the second notification in March 2015 began frequenting the food bank in February 2015.
Frozen beefburgers from three different lots were analysed from the homes of three cases.
All available burgers were sampled two to three times. Analysis of 14 samples in six burgers from one lot yielded 12 positive results for S. Enteritidis, the other lots were negative.
All lots from the Polish producer were blocked in March 2015 before being recalled.
Analyses of remaining lots based on a sampling plan by the ANSES identified additional contaminated lots covering a production period of several months.
The researchers said the specificity of the distribution chain for food banks presented challenges for trace-back and management of remaining product.
“The frozen beefburgers were obtained through bids by producers for the Fund for European Aid to the Most Deprived (FEAD) and there is no commercial relationship between the food banks receiving products and the Polish producer.”
“Outbreak of Salmonella Enteritidis linked to the consumption of frozen beef burgers received from a food bank and originating from Poland: Northern France, December 2014 to April 2015”
Authors: G Jones, N Pihier, C Vanbockstael, S Le Hello, S Cadel Six, N Fournet, N Jourdan-da Silva