Healthy people get sick all the time from bacteria, viruses, fungi... you do not even need a compromised immune system to become ill from salmonella, why do you think healthy people come down with " food poisoning" all the time?
They wouldn't necessarily be able to track it back to a beard, they would record it as "foodborne" unless they specifically tested the persons beard, which is highly unlikely. They usually do not even find how someone became infected, they more often than not just treat the symptoms unless they have reason to believe there was widespread contamination involved that needed a recall, then they may come back and ask questions later, and not about beards. LOL
Hell we don't even keep track of whether or not a patient even has a beard the vast majority of the time. Then again, maybe after this study they will have reason to.