Pyrexia in a young infant - is height of fever associated with serious bacterial infection?

Febrile infants ≤ 90 days old make up a significant proportion of patients seeking care in the emergency department (ED). These infants are vulnerable to serious bacterial infections (SBIs) and early identification is required to initiate timely investigations and interventions. We aimed to study if height of an infant's temperature on presentation to the ED is associated with SBI.

We performed a retrospective chart review on febrile infants ≤ 90 days old presenting to our ED between 31^st March 2015 and 28^th February 2016. We compared triage temperature of febrile infants with and without SBIs. We presented sensitivity, specificity, positive and negative predictive values (PPV and NPV) of fever thresholds at triage. A multivariable regression was performed to study the association between height of temperature and the presence of SBI, and presented the adjusted odds ratio (aOR) with corresponding 95% confidence intervals (CI).

Among 1057 febrile infants analysed, 207 (19.6%) had a SBI. Mean temperature of infants with a SBI was significantly higher than those without (mean 38.5 °C, standard deviation, SD 0.6 vs. 38.3 °C, SD 0.5, p < 0.005). For temperature ≥ 39 °C, sensitivity, specificity, PPV and NPV for SBI was 15.5% (95%CI 10.8-21.1%), 90.4% (95%CI 88.2-92.3%), 28.1% (95%CI 21.1-36.3%) and 81.4% (95%CI 80.5-82.4%) respectively. The height of fever was consistently associated with SBI after adjusting for age, gender and SIS (aOR 1.76, 95% CI 1.32-2.33, p < 0.001). However, 32 (15.5%) infants with SBIs had an initial triage temperature ≤ 38 °C.

A higher temperature at triage was associated with a higher risk of SBI among febrile infants ≤ 90 days old. However, height of temperature must be used in conjunction with other risk factors to identify SBIs in young infants.