Outcomes
The primary outcome was incident diarrhea,defined as 3 or more loose or watery stools in 24 hours.We did not consider individuals who reported an episode of diarrhea or vomiting in the 3 days before enrollment at risk. Secondary outcomes for attributable risk calculations included incident gastrointestinal illness, defined consistently with previous studies as (1) diarrhea, (2) vomiting, (3) nausea and stomachache, or (4) nausea or stomachache and missed regular activities as a result of illness; days of missed work, school, or vacation owing to any gastrointestinal illness;days of missed paid work owing to gastrointestinal illness; and medical consultations associated with gastrointestinal illness, including telephone consultations,inpatient or outpatient care, and emergency room visits.