Hyperpyrexia among infants younger than 3 months.

OBJECTIVE: To determine the prevalence of serious bacterial infection in infants younger than 3 months with fever > or =40 degrees C.

METHODS: We retrospectively identified all infants younger than 3 months with fever who presented to a pediatric emergency department. The medical records were reviewed. The prevalence of serious bacterial infection (SBI) among those patients with hyperpyrexia was compared with febrile infants with lower fever.

RESULTS: 5279 infants younger than 3 months with fever were reviewed. Ninety-eight patients (1.7%) had triage temperature > or =40 degrees C rectally. Median age, temperature, and white blood count for those with hyperpyrexia were 58 days (interquartile range [IQR] 36-78 days), 40.2 degrees C (IQR, 40.0-40.4 degrees C), and 10,800/mm3 (IQR, 7900-14,600/mm3), respectively. Diagnostic studies included blood culture (100%), urine culture (100%), lumbar puncture (100%), chest radiographs (34%), and stool cultures (11%). SBI was found in 38% infants with hyperpyrexia: urinary tract infection was the most common SBI (71%). Among patients with hyperpyrexia, patients with SBI had similar mean white blood cell counts (14,000 vs. 10,200 cells/mm3) and age (54 vs. 53 days) as those with hyperpyrexia but no SBI. The prevalence of SBI among febrile infants with temperatures > or =40.0 degrees C was 38% (95% CI 27-48%) compared with those with fever < or =40 degrees C: 8.8% (95% CI 8.1-9.5%).

CONCLUSION: Hyperpyrexia is rare among febrile infants younger than 3 months. One-third of infants with temperature > or =40.0 degrees C had SBI. Future management algorithms might include hyperpyrexia as a risk factor for serious infection.