Fever Severity and Urinary Tract Infection Risk in Well-Appearing Febrile Infants Aged 61-90 Days.

To analyse the relationship between fever severity and the rate of urinary tract infection (UTI) among well-appearing febrile infants aged 61-90 days with fever without a source (FWS). We conducted a sub-analysis of a multicentre retrospective study between 2011 and 2022. 239 (21.4%) were diagnosed with UTI. UTIs were more common in males (odds ratio [OR]: 2.5; 95% confidence interval [CI]: 1.7-3.3), in infants with a longer fever duration (OR: 1.02; 95% CI: 1.01-1.03), and higher temperature (OR: 1.6; 95% CI: 1.2-2.2). The AUC for predicting a UTI based on fever degree was 0.59 (95% CI: 0.54-0.63). The prevalence of UTI was 22.3% (95% CI: 18.8%-26.1%) in infants with a temperature < 38.5°C, 12.5% (95% CI: 9.2%-16.4%) in infants with temperature 38.5°C-38.9°C, and 32.3% (95% CI: 26.5%-38.5%) in infants with temperature ≥ 39°C. The prevalence of invasive bacterial infection among patients diagnosed with UTI was 3.8% (95% CI: 1.7-7.0), with no significant differences across temperature categories. A urine dipstick test should be recommended for all well-appearing infants aged 61-90 days with FWS regardless of the degree of fever. Blood culture should also be considered in infants with abnormal urine dipstick results, irrespective of fever severity.