Evidence of Multiple Infections in Cases of Diarrhea Due to Enterotoxigenic Escherichia coli

In a surveillance study of diarrhea due to heat-labile toxin-producing Escherichia coli , three E. coli colonies from each patient were tested for their ability to produce heat-labile toxin. The phage sensitivity pattern (phage pattern) of E. coli was also tested to identify the different strains of enterotoxigenic E. coli (ETEC), based on the assumption that colonies giving an identical phage pattern belonged to the same strain. Although all three colonies were toxigenic, they had different phage patterns in about one-third of the cases, a result suggesting simultaneous infection with more than one type of ETEC. The authors examined whether this occurrence could be further verified by parallel variability using other criteria.