Does extreme leukocytosis predict serious bacterial infections in infants in the post-pneumococcal vaccine era? the experience of a large, tertiary care pediatric hospital

Extreme leukocytosis, defined as a peripheral white blood cell count greater than 25,000/mm³, may alarm clinicians and prompt extensive evaluation in infants with fever, especially in the pediatric emergency department. Methods We reviewed data from children aged 3 to 36 months with extreme leukocytosis, fever and the risk of serious bacterial infections (SBI) at our institution from July 2010 to December 2012, a period after the universal introduction of pneumococcal vaccine. Results Serious bacterial infection was recorded in 57 (39%) of the 147 infants. The most common SBI were segmental or lobar pneumonia, in 28 (19%) patients, and urinary tract infection in 16 (10.9%) patients. Three patients had positive blood cultures, corresponding to a bacteremia rate of 2%. C-reactive protein was significantly higher in the SBI group than in the non-SBI group. Conclusions All well-looking febrile infants with white blood cell greater than 25,000/mm³ should undergo a chest radiograph unless there are clear physical findings that indicate a different etiology. Urine culture should be considered in women. C-reactive protein can have an added value in the differential diagnosis.