Simon,
Food poisoning are normally classified into several categories. It may not necessarily mean that the workers may not be able to work.
Assuming that the food poisoning attack is mild and he is medically certified fit to work except for the occasional need to "take a break", you may want to remove him from the production line and transfer him to work in a low risk area.
However, if he is medically found to be unfit to work, I guess evidence is needed to convince Management that his sickies should be given. That will depend on how you deal with your panel of doctors. As long as a valid Medical Certificate is provided by the worker, there is no dispute.
Most organizations have sick-pay schemes and Management relies entirely on the integrity of their panel doctors to make and do the right thing, professionally. Of course, trending of doctors giving Medical Certificate freely warrants attention and that includes the workers track records as well. This is why there is always an annual limit to the number of payable sicky days OR the value of the sick pay whichever is lower.
Many ways to skin this cat. That depends on how the relationship is valued between Management and the Workers.
Charles Chew