A Comparison of Temperature Thresholds to Begin Laboratory Evaluation of Well-Appearing Febrile Infants

Young infants who develop fever are at an increased risk for serious infection. It is unclear, however, what temperature cutoff would be optimal to begin evaluating these infants because some criteria use different thresholds. We sought to determine the percentage of infants presenting to the Emergency Department (ED) with a temperature less than 38.2°C who develop serious infection compared with those with higher temperatures.

We used a publicly available dataset from the Pediatric Emergency Care Applied Research Network. Patients were included if they were aged 60 days or younger, had a documented rectal temperature of 38.0°C or higher in the ED or a history of fever within 24 hours before presentation to the ED, and were being evaluated for serious infection. We used the same exclusion criteria as the original Pediatric Emergency Care Applied Research Network study but further excluded those who were ill-appearing (Yale Observation Score > 10). Serious infections included any of the following: urinary tract infection, bacteremia, bacterial or herpes meningitis, bacterial pneumonia, or bacterial enteritis. Data were described using frequencies (percentages) and compared between groups using χ 2 test.

Of the 4619 eligible infants, 1311 (28.4%) had a temperature lower than 38.2°C. Infants with temperatures lower than 38.2°C were significantly less likely to have a serious infection compared with those with higher temperatures (97 [7.5%] vs 365 [11.2%], P < 0.001). Of the infants with temperatures lower than 38.2°C who were tested, 67 (5.8%) had a urinary tract infection, 10 (0.8%) had bacteremia, 3 (0.4%) had bacterial meningitis, 3 (2.9%) had herpes meningitis, 17 (4.5%) had bacterial pneumonia, and 2 (4.8%) had bacterial enteritis.

In this study, we found that infants with temperatures lower than 38.2°C were significantly less likely to have a serious infection than those with higher temperatures. Using an evaluation cutoff of 38.2°C, however, would likely miss a clinically important number of well-appearing infants with serious infections.