Hospitalizations Due to Respiratory Syncytial Virus Outside of the Typical Season

Objective: Respiratory Syncytial Virus (RSV) is the most common cause of bronchiolitis and viral lower respiratory tract infections in children. It is associated with annual winter epidemics across the United States, typically October through April. Our objective is to describe the clinical characteristics of children hospitalized outside the typical RSV season and to compare them with those admitted during the season. Methods: A retrospective chart review was conducted of all patients who were hospitalized at Children's Hospital of Austin from May 2000 to September 2006 and had a positive RSV antigen test. Descriptive statistics, tests of differences, and associations between patients diagnosed in the off-season versus typical season were conducted. Results: A total of 850 charts of RSV-positive cases were reviewed. Of these, 45 patients (5.3%) were admitted during the off-season. The following variables were statistically significantly associated with diagnosis in the off-season versus typical season: mean birth weight (2704 g vs. 3204 g respectively, p =0.0001); gestational age at birth less than 36 weeks (OR=4.35; 95% CI: 2.2, 8.6); history of neonatal intensive care unit (NICU) admission at birth (OR=6.04; 95% CI: 2.9, 12.5); and multiple birth (OR=3.38; 95% CI: 1.2, 9.2). Conclusions: Infants with RSV infection outside of the typical season were more likely to have been premature, of lower birth weight, the products of multiple births, and admitted to the NICU at birth.