The relationship of Esch. coli 0.26, 0.55 and 0.111 to the incidence and spread of infantile gastro-enteritis in a defined area has been studied over a period of 5 years in the Public Health Laboratory, Southampton.

In the main, the study was concerned with infants up to 1 year of age suffering from gastro-enteritis, and from this age group faecal specimens from 1234 individuals were examined for three sero-types of Esch. coli (0.55 and 0.111 from the autumn of 1949 until September 1954 and 0.26 from May 1953 until September 1954). Esch. coli O.111 was isolated from 66 infants of whom 56 had enteritis, type 0.55 from 159 infants of whom 126 had acute symptoms, and type 0.26 from 14 infants all but two of whom had enteritis.

During widespread outbreaks there were sometimes multiple foci of infection. The determination of the H-antigen carried by the O sero-types showed, for instance, that the 0.55 outbreak in 1952 was almost entirely due to subtype 0.55 H.2, but that a second subtype 0.55 H.7 was also incriminated. Similarly, an 0.111 outbreak in 1953 was due to a mixture of two subtypes (0.111 H. 2 and 0.111 H. 12), but in 1954 the former subtype was not seen and only O. 111 H. 12 was identified.

During epidemic times Esch. coli 0.55 was isolated from 37·2% of the infants examined, whereas in non-epidemic periods the figure was only 1·2%. In the case of type 0.111 the figureswere 26·9 and 1·4% respectively.

Symptomless excreters were found throughout the period of the study and at all ages, but the proportion as compared with cases was significantly higher in children over 1 year of age. Nevertheless, there were several symptomless excreters less than 4 weeks old. While there was some evidence to suggest that the young child who was a symptomless excreter might be responsible for maintaining a low-grade infection in a community, there was no indication that the rare adult-carrier played any significant part in this.

The specific types of these coliform organisms can survive for long periods outside the body. Naturally infected dust contained viable organisms 12 days after it was first found to be so contaminated; the dust was maintained in a cool shady room.

There is great variety in the clinical severity of the disease as seen in comparable groups of infants, from a very grave illness to the very mildest of diarrhoeas. The very young and those with some other complicating illness are always at a greater risk.

The pattern of the outbreaks as seen in this study suggests a gradual enhancement of virulence of the two main types of Esch. coli with local spread at first and then wide dispersal throughout the district followed by a reversion to the poorly invasive type.