Predictors of a normal chest x-ray in respiratory syncytial virus infection

Respiratory syncytial virus (RSV) accounts for the majority of lower respiratory tract infections (LRTI) in infants and young children. A chest x-ray is frequently performed in infants with LRTI caused by RSV. The aim of this study was to develop and validate a prediction model to estimate the probability for a normal chest x-ray in children with RSV infection. For this purpose, easy obtainable diagnostic parameters were used. This prediction model may be applied to decide which patients do not require a chest x-ray. The data of 287 children admitted with RSV infection or diagnosed as such in the outpatient department of the Sophia Children's Hospital between 1992-1996 were studied. The derivation set comprised 232 patients (1992-1995), and the validation set contained 55 patients (1995-1996). A chest x-ray was designated as normal when atelectasis, hyperinflation, or pulmonary infiltrates were absent. In order to develop a prediction model, patient history and clinical and laboratory variables were consecutively entered into a logistic regression model according to the diagnostic workup that was practiced at the time. Variables with P ≤ 0.10 were retained in the model. The predictive accuracy of the multivariable models was examined using the area under receiver operating curve (ROC-area). In 202 (87%) patients from the derivation set, a chest x-ray was performed. A normal chest x-ray could be predicted by increasing age, increasing birth weight, presence of rhinitis, absence of retractions, and increasing arterial oxygen saturation. The ROC-area was 0.80 in the derivation and validation sets. This prediction model was transformed into a score chart. In conclusion, a normal chest x-ray can accurately be predicted, using a model including easily obtainable patient characteristics, and clinical and laboratory variables. This model may be a useful tool in deciding whether or not to perform a chest x-ray in patients with RSV infections.