Does extreme leukocytosis predict SBI in infants?

White blood cell (WBC) count, even extreme leukocytosis, does not predict serious bacterial infection (SBI), according to authors of a recent study. These investigators conducted a retrospective chart review of 147 well-appearing children aged 3 to 36 months with a fever higher than 38°C and a WBC count above 25,000mm³. The children were seen in the emergency department of an Israeli hospital after pneumococcal vaccines had been universally introduced. Investigators then compared rates of SBI in their study population with those found in studies conducted before the introduction of Haemophilus influenzae type B (Hib) and the 7 serotype pneumococcal (PCV7) vaccines.

Next: Docs spread out vaccines despite concerns

Children in the study group had blood cultures drawn, and most had chest radiography, along with urine cultures in 56 (38%). An SBI was diagnosed in 57 patients (39%). 

Investigators found the 2% rate of SBI in this study, conducted after Hib and PCV7 vaccinations began for  all infants, is similar to the 2.3% to 2.7% of SBI in children with extreme leukocytosis found in 2 studies conducted in the post-Hib vaccine era but before the introduction of PCV7 vaccine. These rates of SBI compared with 19% found in a study conducted in the pre-Hib era.

The authors recommend that all febrile infants with extreme leukocytosis undergo a chest radiograph and that urine culture be considered in females (Danino D, et al. Pediatr Emerg Care. 2015;31[6]:391-394).

Commentary: In their discussion, these authors state that a markedly elevated WBC does not predict SBI, “as shown by the fact that only 39% of our children with extreme leukocytosis actually had SBI.” Well, 39% is enough to make me sit up and pay attention! Most children with these numbers don’t have SBI, and perhaps even fewer do now with the subsequent introduction of PCV 13. However, we should still think twice when we see WBCs in this range, and when we do, acknowledging that common things are common, we should follow the authors’ advice regarding chest x-rays and urine cultures. -Michael G Burke, MD

Ms Freedman is a freelance medical editor and writer in New Jersey. Dr Burke, section editor for Journal Club, is chairman of the Department of Pediatrics at Saint Agnes Hospital, Baltimore, Maryland. The editors have nothing to disclose in regard to affiliations with or financial interests in any organizations that may have an interest in any part of this article.