Lack of usefulness of an abnormal white blood cell count for predicting a concurrent serious bacterial infection in infants and young children hospitalized with respiratory syncytial virus lower respiratory tract infection

Background: There continues to be controversy on the most appropriate way to manage infants and young children with fever and documented RSV lower respiratory tract infection (LRTI). The objective of this study was to determine the usefulness of an abnomial white blood cell (WBC) count for predicting a concurrent serious bacterial infection in patients admitted with RSV LRTI. Methods: The medical records were reviewed of patients discharged with RSV LRTI during the 5 RSV seasons from July 1, 2000 through June 30, 2005. Data were collected on age and gender as well as temperature, complete blood count with manual differential and bacterial cultures obtained at admission. Results: The inclusion criteria was met by 1920 patients. There were 672 febrile patients who had a complete blood count and a bacterial culture. One (5.0%) of 20 patients with a WBC < 5000 had a positive culture, 23 (4.7%) of 492 patients with a WBC 500014,999 had a positive culture, 5 (4.8%) of 105 patients with a WBC 15.000-19,999 had a positive culture, 2 (5.7%) of 35 patients with a WBC 20,000-24,999 had a positive culture, none of 11 patients with a WBC 25.000-29,999 had a positive culture and 3 (33%) of 9 patients with a WBC > 30,000 had a positive culture. Overall, cultures were positive in 34 (5.1%; 95% CI: 3.4-6.8%) of the febrile patients tested and almost all (32; 94%) showed positive urine cultures. Conclusion: The probability of an abnormal WBC count < 5000 and 15,000-30,000 being associated with a concurrent serious bacterial infection was very low and no different from that of a normal WBC count in febrile patients admitted with RSV LRTI.