Background and Aim Diagnosis of a serious bacterial infection (SBI) in young children can be challenging. Clinical features at presentation are used to guide investigation and management. We aimed to determine whether tachycardia is associated with a higher risk of SBI.

Methods Prospective cohort study of children < 6 years old referred to a children’s acute assessment unit with documented or reported temperature (July 2011 - February 2012). We examined the association between maximum heart rate during admission (Heart rate: ≥90^th percentile for age corrected for temperature) and confirmed SBI (defined as per NICE guidelines).

Results 120 children participated. 37 children were tachycardic. 21 children had a confirmed SBI.

Conclusions In this cohort of young children referred to an acute assessment unit with fever, the presence of tachycardia did not predict reliably SBI, but absence of tachycardia excluded SBI in 95% of children.