ST. LOUIS - Local doctors are warning parents of young children to be on the lookout for Respiratory Syncytial Virus or RSV.

There have been 51 confirmed cases at Cardinal Glennon Hospital this month and 118 cases at St. Louis Children’s Hospital this week. That number can be even higher because a lot of times doctors treat the symptoms without even testing. Doctors expect the numbers to climb as we get deeper into winter.

One of the babies on the mend at Cardinal Glennon is Seamus Grinnan. He spent his first Christmas in the hospital recovering from the respiratory virus.

"We were steaming him in the bathroom and starting to break up some mucus with the hot shower steam," his mother Jessica Grinnan said.

Nothing worked, so she brought him in to Cardinal Glennon thinking he was suffering from a really bad cold only to find out Seamus was battling RSV.

Dr. David Wathen at Cardinal Glennon said RSV inflames children’s airways.

"They start to look like they are working really hard to breathe,” Dr. Wathen said. “Their oxygen saturations start dropping. You see the stomach sucking in. In between the ribs, the ribs become defined when they breathe."

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The symptoms are similar to a common cold: runny nose, chest congestion and coughing.

The best way to prevent it is to wash your hands often and keep babies away from second-hand smoke. Dr. Wathen said the virus makes babies want to feed less.

“If they have less than one diaper every eight hours, that's a sign they are becoming dehydrated," he said.

Because of his treatments, Seamus can’t feed normally.

"He thinks he's hungry this whole time, he does his little hungry cries,” his mother said. “All you can is give him his sweeties to calm him down so he goes back to sleep."

RSV typically lasts two weeks and primarily affects babies under the age of 2.

If you think something’s wrong, get your child checked out, especially this time of year, Grinnan said.

There is a vaccine available, but it's reserved for the most vulnerable babies. The vaccine is called Synagis. According to the vaccine's website, "SYNAGIS gives babies who are born prematurely (at or before 35 weeks, and who are 6 months of age or less at the beginning of RSV season) the infection-fighting antibodies they lack, helping protect their vulnerable lungs from RSV."