Cranberry and cranberry-lingonberry juice prevented urinary tract infections in children and in adults in our earlier clinical trials. The preventive effect was, however, observed late in the follow-up and the next recurrence was not prevented in children. The investigators hypothesize that cranberry-lingonberry juice should be started already during the antimicrobial treatment of acute urinary tract infection in order to maximize the preventive efficacy of the juice. In addition, the investigators aim to find the explanation for the efficacy of cranberry-lingonberry juice by analyzing the concomitant changes in the chemical composition of urine and feces as well as the changes of gut microbiota.

Inclusion Criteria:

• Recent confirmed urinary tract infection, diagnosed in Oulu University Hospital or Oulu Health Care Center
• Age 1-16 years

Exclusion Criteria:

• Continuous antimicrobial prophylaxis
• Age < 12 months or > 16 years
• Severe congenital kidney or other urinary tract anomaly in ultrasound