Several people came down with an illness caused by a type of bacteria in seafood  Health officials traced the history of each person who became ill to the same restaurant and date  Careful testing showed that most people who ate seafood at the restaurant on that date had not come in contact with the bacteria in question
Despite this finding, health officials remained confident that contaminated seafood from this restaurant caused the cases of illness
All and only those who ate contaminated seafood at the restaurant on that date were allergic to the monosodium glutamate in a sauce that they used.