How should restaurants effectively respond to a customer report of food poisoning?

a functional Crisis Management system should be in place . An establishment should be able to develop an organized and systematic handling of incidents of such kind. Food poisoning is a very serious issue that if not carefully handled, it could result to legal actions, fines/penalties, payment of damages (especially if it resulted to fatality) and worse loss of reputation. As what Mr. Arnido and Yassin have mentioned it should first start on the determination of "Who is the customer?" , a quality root cause analysis is very important in this stage as it  is where you will conclude if your establishment is liable because of negligence done from your establishment  or it might be there are other contributing factors that leads to such incident to happen which might get you out of the hook. Proper coordination to the victim, authorities and media is cruicial at this stage that is why the company should assign someone who is competent to do the task. All staff of the establishment should also know these procedures (they should know who should talk first to govt. investigators, who should talk to the media, who should talk to the family of the victim and to whom should they report if such incident happen)

First, the restaurant must determined if the customer has eaten in your restaurant on that particular day. If so, ask what time the customer eat in your restaurant and what kind of food he/she had ordered. Please note that the symptoms of a particular food poisoning starts within2 to6 hrs from the time of intake. The restaurant must respond immediately to show concern for the customer during the incident. The customer must not be sidelined in order settle the issue. Thanks.

all the above are totally right, but we can manage that case by case, i am not talking about basics and steps that we learn in school and collage as its one of the most complicated issues at restaurant , reality and facing the problem face to face are two different things. means you have to know your guest wants and what his looking after? is he right or wrong? is that happened in the restaurant or not.? are not a matter. the matter is to understand his needs and to limit the damages. some customers wants to be sure that will not happen again and we should strongly promise him and work to do our promise, some will file a case then its a lawyer work not your work( we all know about restaurants was closed or payed a millions because of such mistake) and some other will ask for some benefits where it solved it self. however a good manager should not let it reaches that point. strong manager and team leader has no food poisoning at his restaurant.

Just like mr arnido mentioned you first should determine the timing of order and specify what kind he has ordered, In the meanwhile you should act serious with carefully listening and paying attention's as well in order to act immediate with the incident.

Hygiene and continuous monitoring of the quality