Acquisition of nonmaternal Enterobacteriaceae by infants delivered in hospitals.

To determine whether Escherichia coli strains that colonize the intestinal tract of newborn infants in hospitals are of maternal origin or come from the environment, plasmid profiles of E. coli strains isolated from the stools of infants were compared with those from the stools of their mothers. Twenty-nine mother-infant pairs were studied in three different hospitals. In only 4 of 29 pairs, plasmid profiles of E. coli or other Enterobacteriaceae were shared by infant and mother; vertical transmission seemed to be uncommon, unlike findings in previous reports. In one hospital, 8 of 10 infant fecal E. coli strains shared a single plasmid profile, strongly suggesting nosocomial acquisition. In another, 7 of 9 neonate strains also shared a unique profile, and additionally carried K1 capsular antigen, a known virulence factor. Two other infants from the latter nursery acquired a urinary tract infection with E. coli K1 carrying the same plasmid profile. This study indicates that nosocomial acquisition of hospital strains of E. coli by neonates may be common in some hospitals and that the clinical implications are potentially serious.