A case of gastrointestinal illness was defined as illness in a student or staff member who reported nausea, vomiting, or diarrhea and who was present at the school any time during February 2-18. A questionnaire was developed to use in a cohort study of all staff members and students. Because no food was served at the school other than lunches that students brought from home and prepackaged snacks served in prekindergarten classes, foodborne transmission was not suspected; questions focused on illness onset, symptoms, school grade,
classroom, special classes (e.g., art), ill contacts, and use of certain facilities or equipment (e.g., library computers) or participation in certain programs (e.g., after-school programs). Questionnaires were sent home by the school principal with all staff members and students the afternoon of February 9. The school nurse identified additional cases beginning February 9 by visiting each classroom daily;
she interviewed persons who became ill during school and interviewed absent ill persons or a family member by telephone regarding grade,
classes, illness onset, and symptoms. Information regarding ill contacts,
facility and equipment use, and participation in programs was unavailable from the participants enrolled by the nurse.