If no institutional guideline is available, we will apply a standardised definition of low-risk (box 1).1 2 For the purposes of inclusion in the study database, the standardised definition will use only those laboratory values that are consistent across all institutional and national guidelines from the study time period. This is intentionally broad so as to maximise sensitivity in identifying all infants potentially considered low-risk during ED evaluation.

Negative urine leucocyte esterase

AND

Negative urine nitrite

AND

Urine white blood cells<10/hpf

AND

White blood cell count>5000 cells/µL and <15 000 cells/µL