What finding would best aid in the confirmation of a respiratory viral infection in the infant with wheezing?

The rapid antigen test for respiratory syncytial virus (RSV) is particularly valuable in confirming a respiratory viral infection in infants who present with wheezing. RSV is a common cause of bronchiolitis and other respiratory illnesses in young children, especially infants under one year of age, and can lead to wheezing and difficulty breathing.

This test is designed specifically to detect the presence of RSV antigens in a nasal swab specimen quickly, allowing for timely diagnosis and management. Early identification of RSV can help guide treatment options and parental education regarding the illness.

Other tests listed, such as the sweat chloride test, are used to diagnose cystic fibrosis and are not relevant for confirming viral respiratory infections. Complete blood count (CBC) with differential may assess for signs of bacterial infection or immune response, but it is not specific for viral infections. Chest ultrasound is not typically employed for diagnosing respiratory infections in this context; it is more useful for evaluating structural abnormalities or complications related to respiratory issues. Therefore, the rapid antigen test for RSV is the most appropriate choice for confirming a respiratory viral infection in an infant with wheezing.