The PED at Queen Silvia Children’s Hospital is the only PED in the Gothenburg metropolitan area, serving nine municipalities. With approximately 60,000 annual visits, it is the largest PED in the Nordic countries. All infants younger than 3 months presenting with fever between October 1, 2022, and November 11, 2023, were eligible if they had a negative dipstick test. To explore whether routine urine cultures may be unnecessary in carefully selected low-risk cases, infants with previous UTI or increased susceptibility to UTI (e.g., urinary tract reflux or other anomalies) were excluded.

At our PED, clean-catch urine is the first-line method for UTI screening. If the clinical history or symptoms suggest UTI, or if the initial sample indicates UTI, suprapubic aspiration is performed for culture. For participants in this study, who had neither a history nor a dipstick suggestive of UTI, most cultures were based on clean-catch samples.

This was a prospective, single-center observational study. Medical chart review included data on age, sex, temperature, symptoms, systemic inflammatory markers (C-reactive protein [CRP], interleukin-6), length of hospital stay, antibiotic treatment (agent and duration), urine culture results, and follow-up within 3 months.

Fever was defined as ≥ 38.0 °C measured at any site (rectal, ear, axillary, or forehead), either at home or in the PED. A dipstick was defined as negative if all of the following were absent: leukocytes, nitrite, erythrocytes, protein, glucose, and ketones. Strict criteria for clinically relevant febrile UTI were applied. Cultures were deemed clinically irrelevant if any of the following were present: growth of 1000 cfu/ml, mixed bacterial growth, negative inflammatory markers combined with spontaneous resolution of fever without antibiotics, or identical bacterial growth with the same resistance pattern in an asymptomatic period within 3 months.

Categorical variables were presented as counts and percentages. Continuous variables were presented as medians with interquartile ranges (IQR). Categorical comparisons were performed using chi-square or Fisher’s exact test, and continuous variables using the Mann–Whitney U test. A two-tailed p < 0.05 was considered statistically significant. Analyses were performed with SPSS Statistics version 29 (IBM Corp., Armonk, NY, USA, 2025). The study was approved by the Swedish Ethical Review Authority (DNR2024-05919-01), which waived the requirement for informed written consent.