Properties of Escherichia coli isolates from urinary tract infections in boys.

Fifty-five isolates of Escherichia coli from urine of boys younger than three years of age with urinary tract infection (UTI) were compared with strains from girls of the same age range who had UTI. The frequency of P fimbriae, hemolysin, and type 1C fimbriae, previously described as associated with pyelonephritis (PN) in girls, was also high (76%, 60%, and 31%, respectively) in UTI-associated strains from boys. However, in contrast to isolates from girls, strains from lower UTI in boys did not differ from PN-associated strains regarding these three characteristics. In contrast, aerobactin production was significantly associated with PN compared with lower UTI in both sexes. Serotypes O4 and O6 were overrepresented among all UTI-associated strains from boys and PN-associated strains from girls. This overrepresentation was largely accounted for by three clones, one of which was a new clone identified among the UTI-associated strains from boys.