For over a decade it has been recognized that hospital outbreaks of infantile diarrhea due to enteropathogenic Escherichia coli (EEC) can be potentiated by the introduction of EEC serotypes into a nursery population of susceptible newborn or young infants.1Nursery epidemics have appeared to follow either 1 of 2 clinical patterns: There may be a smoldering period of varying duration before the outbreak reaches epidemic proportions,2,3or the outbreak may be explosive with no advance warning.4 Wheeler1has pointed out that the smoldering period may represent a build-up of environmental contamination in the absence of overt diarrhea in the nursery. Indeed, there have been a number of reports concerning the incidence of EEC in asymptomatic infants which have led to several views regarding the predisposition of such infants to overt diarrhea or their role in potentiating an outbreak.3,5-10However, studies of incidence of EEC and