Respiratory viruses occur frequently during the winter season. One virus that affects adults and children but can cause complications for babies under one year of age is respiratory syncytial virus or RSV. In adults and older children, this virus usually causes a cold. In younger children it can cause a cold or something more severe called bronchiolitis. Children with bronchiolitis have wheezing and my have difficulty breathing. They need to be evaluated because they sometimes need extra oxygen or IV fluids to treat dehydration. Contact your doctor if your child has a cold and is breathing very fast, working hard to breathe or having difficulty swallowing. Also, any infant with a cold how is two months old or younger and develops a fever needs to be evaluated promptly.