Though food history information did confirm a link between illness and eating a school lunch, we were unable to identify a particular food item based on this information. The above table presents information from all students - a similar table based on information from 1st and 2nd graders was not helpful because all children in those groups who ate the school lunch became ill. Although epidemiologic studies of this type are an integral part of an outbreak investigation, the reality is that they do not always provide the answer. In this instance, the effectiveness of this method was influenced by difficulties in getting valid information from young children, the absence of well persons in the most highly exposed groups (1st and 2nd graders). Results were also influenced by the fact that the involved food item was consumed by virtually all persons who ate the school lunch but contamination of that food item was not uniform.