One foodborne illness complaint is almost always survivable with the right response. A cluster of complaints from one service date is an emergency. Listen without arguing — get the customer name, phone, what they ate, what time, symptoms. Thank them and say you will investigate. Do not say "we never get complaints" or "must be something else you ate". Inside 24 hours: notify your general liability insurance carrier; pull any remaining product from the same lot in a labeled sealed container in the freezer; review prep and temperature logs; check staff for recent illness. If the health department contacts you, cooperate fully. Your insurance carrier may also assign defense counsel — let them lead communications with the complainant. Document everything in writing. A clean record of prompt investigation is your strongest defense.