Confirming the cause of a food-borne illness is devilishly difficult, public health officials say, especially without a cluster of cases. Consequently, many sickened patrons don’t even bother to report incidents, and many chefs struggle with how to respond when they do.

The CDC estimates that Americans experience 76 million food-borne illnesses a year, with very few of those incidents reported, and even fewer confirmed by laboratory tests. The symptoms are typically similar to those that accompany the flu: diarrhea, vomiting, stomach cramps.

Most people never go to a doctor with their complaint because their symptoms quickly subside, reports Jane Fletcher for the San Francisco Chronicle. Those who do see a physician are rarely tested for food-borne illness because the lab tests are expensive, and the patient probably will have recovered by the time the results come back.

Since 2000, California law has required at least one employee in every restaurant to be certified as a safe food handler. Many restaurants send more than one employee for training and certification. In the eyes of public health officials, the training appears to be working.

Health officials suggest consumers be prepared to tell the restaurant exactly what they ate and drank, what time they dined, and whether anyone who ate with them also experienced symptoms. It’s best not to be demanding or accusatory – there is no proof, after all — or expect the restaurant to confess wrongdoing. But they should receive a sympathetic hearing, an assurance that the restaurant will review its procedures, and a genuine thank-you for taking the trouble to call.