Untreated asymptomatic bacteriuria in girls: I--Stability of urinary isolates.

OBJECTIVE: To assess the frequency of spontaneous changes of bacterial strains in patients with untreated asymptomatic bacteriuria. DESIGN: Retrospective analysis of samples from all patients with renal scarring and random sample of patients with normal kidneys. SETTING: Outpatient clinic for children with urinary tract infections. PATIENTS: 54 Girls aged 3.3-15.5 years with untreated asymptomatic bacteriuria caused by Escherichia coli. INTERVENTION: None. END POINT: Change in bacterial strain. MEASUREMENTS AND RESULTS: Serotyping and electrophoretic analysis of sequential bacterial isolates, representing 151 patient years of untreated asymptomatic bacteriuria. A total of 24 changes of strain were identified. Eleven were related to medical interference such as treatment of other infections with antibiotics. CONCLUSIONS: Spontaneous changes of strain were uncommon, one change in 11.6 patient years, and thus are not a characteristic feature of the course of asymptomatic bacteriuria.