Bronchiolitis is usually diagnosed from the history given by the mother about their child's clinical signs and symptoms.

Most children will start their illness with an upper respiratory tract infection (runny nose, low-grade fever, cough, and poor feeding). One or two days later they may start breathing faster and have a wheeze (a high pitched musical sound heard with the breath). This is due to inflammation and narrowing of the small airways in the lung.

What medical investigations/tests are needed?
Children with a clear clinical diagnosis of bronchiolitis will not normally need a chest X-ray, and blood tests are also not needed for most children.

Testing nasal secretions for the virus (nasopharyngeal aspirate, NPA) should also not be done routinely, as identifying the virus adds little to usual treatment.