Respiratory syncytial virus, known as RSV, is a respiratory virus that infects the lungs and breathing passages, according to the CDC. It's a mild, cold-like illness for most healthy people, but can be dangerous for infants and a cause of bronchiolitis and pneumonia. It can spread through coughing and sneezing and can survive on hard surfaces, such as crib rails, for hours.
Croup is caused by a virus and causes swelling in the trachea and larynx. It's most common in children 1 to 3, according to the American Academy of Family Physicians, and can be spread through coughing, sneezing, through unwashed hands, shared toys or utensils. Among symptoms, it's known for a barking cough.