An abnormal white blood cell count is not a useful marker for predicting concurrent serious bacterial infection in infants and young children hospitalized with respiratory syncytial virus lower respiratory tract infection, results from a large single-center study demonstrated.
The finding is important because although there is a guideline for treating infants and young children with fever without a source (Pediatrics 1993;92:1–12), there is no guideline that addresses the treatment of febrile infants and young children with clinical evidence of viral infection, Dr. Kevin Purcell and Dr. Jaime Fergie said.
The researchers studied the medical records of 1,920 infants and young children admitted to Driscoll Children's Hospital in Corpus Christi, Tex., with respiratory syncytial virus (RSV) lower respiratory tract infections between July 1, 2000, and June 30, 2005 (Pediatr. Infect. Dis. J. 2007;26:311–5).
They defined fever as having a temperature of 100.4° F or higher before admission. The WBC count was considered abnormal if it was lower than 5,000/mcL of blood or it reached or exceeded 15,000/mcL of blood. The median age of the 1,920 patients was 142 days, and 672 had a complete WBC count and bacterial culture.
Overall, only 34 of the 672 patients (5.1%) had a positive bacterial culture. The probability of a WBC less than 5,000/mcL and a level between 15,000 and 29,999/mcL being associated with a concurrent serious bacterial infection ranged from 0% to 5.7%. This was no different from the rate of a normal WBC in febrile and afebrile patients, which ranged from 3.9% to 4.7%. However, patients with a WBC of 30,000/mcL or greater were about six times more likely to have a concurrent serious bacterial infection than those who had lower levels.
“Applying the guideline for treatment of infants and young children with fever without a source to patients with RSV lower respiratory tract infection is of no use in predicting the presence of a concurrent serious bacterial infection. However, we believe [one should] obtain blood cultures in infants with RSV lower respiratory tract infection that have a WBC count of 30,000 per mcL or greater or are toxic-appearing,” they wrote.