Urinary tract infection (UTI) is a frequently suspected cause of fever in young children, justifying urine cultures. Sampling procedures are decisive for the reliability of UTI diagnosis. Even though official guidelines recommend clean catch method, catheterization or suprapubic aspiration, urine bag collection remains widely used. In our experience, the rate of contaminated bag-obtained cultures reaches 30.2 %. In a recent study, the investigators have noticed that the rate of contaminated urine cultures was lower when children were kept in an upright position at the time of urine collection. The upright position could explain this decrease, perineum being less in contact with urine. These results are borderline significant, the investigators would like to confirm them with a specific study.

Inclusion Criteria:

• Children aged 2 - 36 months
• Non-toilet-trained children
• Indication to bag urine collection with the following criteria :
• fever ≥ 38.5 °C
• unexplained fever
• and at least 1 of the following criteria for girls and uncircumcised boys, at least 2 criteria for circumcised boys :
• age ≤ 12 months
• fever ≥ 48 hours
• poorly tolerated fever (chills ± cyanosis ± pronounced weakness…)
• preceding episode of tract urine infection

Exclusion Criteria:

• Parents opposed to the participation of their children in the study
• Diarrhea
• Current antibiotic treatment or during the 8 preceding days of the urine collection
• Genitals / perineal anomaly