Leucocytosis and Risk for Serious Bacterial Infection in Young Children

When infants and toddlers present with fever, the differential diagnosis can range from insignificant viral illness to serious bacterial infection (SBI). White blood cell (WBC) counts >15,000/mm³ (moderate leucocytosis) have been associated with increased risk for occult bacteremia, but less is known about WBC counts >25,000/mm³ (extreme leucocytosis). To examine the association between extreme leucocytosis and SBI, investigators in Israel conducted a retrospective case-control study involving young children (age range, 3–36 months) who were admitted to a single emergency department in January 2007 through June 2008 with fever (temperature >38°C) and who underwent complete blood count as part of their evaluation for fever. Overall, 164 chil…