SIOUX FALLS, S.D. (KELO) — Little Reagan Gruis is doing well today, but it was a different story late last year.

“When we went to the ER for fluids, she wasn’t able to keep anything down,” mother Kristen Gruis said. “It seemed like she was constantly dry-heaving, every time we tried to feed her, she was throwing everything up, and she just didn’t look right. Her color wasn’t right.”

Gruis explains that her little one had RSV at the age of eight months.

“Knowing her oxygen wasn’t where it was supposed to be was kind of the scariest part of it all,” she said.

“Just the aspect of her oxygen levels being low and having to be hospitalized for five days was a lot to deal with,” father Brandon Gruis said.

Regan was hospitalized in Worthington, Minn. An advisory on the CDC’s website says health care workers should watch for more cases of respiratory viruses. RSV, which stands for respiratory syncytial virus, is among these.

“The symptoms are going to be consistent with a lot of other viral infections, cough, congestion, irritability, fussiness, eating less, sleeping less,” said Dr. Justin Kane, who practices emergency medicine for Sanford Health in Worthington.

Kane says that age and symptom severity are linked.

“You can see it at all ages, right, but definitely the younger the child, the more the severe the symptoms,” Kane said.

According to the National Institute of Allergy and Infectious Diseases, across the country almost every child has had RSV by the time they reach their second birthday. If someone is healthy, symptoms typically aren’t bad. But for the vulnerable, like an infant or someone who’s elderly, the illness can be a big problem. Reagan is now making a toddler’s small talk and enjoying a colorful book. Her mom says to put faith in the experts.

“Just trust your health care providers,” she said. “They’re definitely going to be the right ones to diagnose you, and they’re also going to be the ones there to take care of you when something happens.”