The Norovirus outbreak lasted from 20 September to 5 October 2012, according to a report in Eurosurveillance.
390 institutions in five federal states (Berlin, Brandenburg, Thuringia, Saxony and Saxony-Anhalt) reported nearly 11,000 cases of gastroenteritis.
Robert Koch Institute (RKI), the Federal Institute for Risk Assessment (BfR) and the Federal Office of Consumer Protection and Food Safety (BVL) were involved in the investigation.
Stopped 11,000 illnesses?
Stopping deliveries and recalling the product ensured at least 1,136 boxes (more than 11 tons) of strawberries from the incriminated lot did not reach the consumer, said the report.
The remaining 1,065 boxes had already been used or were destroyed under the supervision of the local food safety authorities.
“Assuming a similar level of contamination in the part of the lot that was withdrawn, at least 11,000 cases were averted by the withdrawal, probably even more, seeing as only a fraction of the delivered strawberries had been prepared for consumption,” said the report.
Saxony's State Health Laboratory detected Norovirus in a sample obtained from an unopened box of the incriminated lot of frozen strawberries in October.
Imported from China
All affected institutions had received strawberries imported frozen from China from a sub-contractor of the catering firm Sodexo.
According to the German Task Force on Food and Feed Safety, some of the involved regional kitchens reported not having heated the strawberries during preparation while others said they had, which may explain that not all institutions reported cases of gastroenteritis.
On 27 September 2012, the public health authority of Brandenburg informed the RKI about several outbreaks of gastroenteritis in schools and childcare facilities amassing to at least 500 cases.
At least 38 people required hospitalisation; the majority of illnesses were of short duration and self-limiting.
From 1 January 2013, a European Union (EU) regulation requires 5% of consignments of frozen strawberries imported from China into the EU to be tested for norovirus.
Global trade effect
The authors said that findings exemplify the risk of large outbreaks in the era of global food trade.
“Today, unprecedented volumes of produce (here 22 tonnes) are distributed to a large number of markets throughout the world, thereby increasing the risk for food safety.
“Public health surveillance needs to adapt to these challenges, e.g. be able to detect outbreaks caused by widely disseminated foods.
“Surveillance using molecular subtyping information allows establishing links between disease occurrences in different regions, usually seemingly sporadic cases or small clusters.”
“Large multistate outbreak of Norovirus Gastroenteritis associated with frozen strawberries, Germany 2012”
Authors: H Bernard, M Faber, H Wilking, S Haller, M Höhle, A Schielke, T Ducomble, C Siffczyk, S S Merbecks, G Fricke, O Hamouda, K Stark, D Werber