But local officials say the outbreaks point to the need for increased education for food handlers.
It was discovered that the British food handlers were the least likely to wash their hands after using the restroom.
Ministers are empowered to require hygiene training for food handlers.
A frequent cause is a food handler who does not wash his or her hands with soap after using the bathroom.
In addition, a state-certified "food handler" must be on staff at all times.
Foods other than shellfish may be contaminated by infected food handlers.
Some experts recommend that food handlers be tested for the presence of the bacteria after they recover.
The government has announced that it is planning to launch a training programme for all food handlers.
I suggest you check your kitchen and your food handlers.
However, no food handler has been identified as a potential source of transmission.