Epidemiological tracing of Escherichia coli by O antigen typing in a geriatric ward

The nosocomial spread of Escherichia coli in a geriatric ward was analyzed with sampling at intervals of 2 weeks for 1 year. Specimens were obtained from patients, staff, and hospital environment and 5 239 E. coli colonies were O grouped into 49 O antigens. About 29% of the patients acquired bacteriuria during the hospitalization. In 75% of the bacteriuric strains the same O antigen was found in urinary and faecal samples from the same or the previous sampling round. Nosocomial spread of E. coli could be shown. Cross-infection as well as auto-infection were considered to be the modes of spread.