Do you feel confident in your product and cooking processes? Are you certified and are your managers? If so, kindly advise the customer that you are going to ask for an emergency inspection and ask the health dept. to test the product.
Also, advise them that your supplier and your attorney will be contacting them as part of the investigation and you WILL get to the bottom of it for both your sake and theirs.
Finally, kindly ask them to go to the hospital and have their stool tested.
NOW…if it is a legitimate complaint…they WILL NOT go to the hospital because they are afraid of being caught. If they do, and it comes out positive…the hospital test will tell you the who, what where when.
Lastly, APLOGIZE if it is true and this is why you have Liability Insurance.
Happened to me twice…and neither of the two went to the hospital and BOTH still order…but there is a little note in their file incase they think we forgot.
GOOD LUCK and believe in your product.