Hospitals and health departments are struggling to respond to an early and surprising surge of cases of RSV — respiratory syncytial virus — which is striking children across the country. 

RSV is described as a very common respiratory virus that usually causes mild, cold-like symptoms, according to the Centers for Disease Control and Prevention (CDC).

Most people recover within two weeks — but RSV can be serious, especially for the very young or very old and those with compromised immune systems. 

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"Hospitals from New York to Connecticut to Illinois to California to here in Texas and Oklahoma — we are seeing cases of RSV surge beyond what is expected for this time of year," reported Dr. Laura Romano of Cook Children’s Medical Center in Fort Worth, Texas, a pediatric hospital at which patients are arriving from surrounding states. 

"It is not uncommon for me to see a child from Oklahoma, New Mexico, Louisiana, who has been sent to Cooks because the hospitals in their state do not have any more beds for them," the same doctor said. 

The Connecticut National Guard confirms the organization sent a representative to a site feasibility meeting to discuss a potential "mobile field hospital" at Connecticut Children’s Medical Center in Hartford. 

The planning is viewed as "pre-decisional."

At M Health Fairview Masonic Children’s Hospital in Minneapolis, Minnesota, the swiftness of care is being impacted, Fox News is told. 

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"All of a sudden our volumes have gone way up, and so we are very busy in the emergency room, which is increasing wait times," said Dr. Marissa Hendrickson, a pediatric emergency medicine physician. 

"We are sometimes caring for people in the waiting rooms, hallways, wherever we can squeeze them in."

About RSV, Dr. Janette Neshewiat, a Fox News medical contributor who is based in New York City, said, "This is a virus that can cause inflammation in the lungs. It can cause infection in the lungs like pneumonia."

She added, "And what we're seeing now is it's causing about 60,000 hospitalizations in children every year. For every three children that are hospitalized with COVID, we're seeing up to 30 hospitalized with RSV."

Many experts in the health field believe the surge in cases may be related to COVID-19 mitigation efforts. 

"Because of the pandemic and people isolating themselves from each other, several of these young children did not develop an immune response to … ordinary, common, everyday viruses," said Dr. Sankaran Krishnan, a pediatric pulmonologist at Maria Ferari Children’s Hospital in Valhalla, New York. 

While many cases of RSV resolve without advanced medical care, children who show signs of breathing trouble should seek immediate care. 

"If your child starts developing respiratory distress, breathing faster than usual, that belly going in and out with every breath, the skin between their ribs being sucked in with every breath — that's when they need to be seen by a provider as soon as possible," said Dr. Romano. 

"Take them to an urgent care. Take them to an emergency room," she added. "If at any point it looks like your baby is not breathing well at all, just bring them right to an emergency room."

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Doctors advise a variety of measures to help avoid illness, from handwashing to mask wearing — with concerns for a difficult winter and the potential for another COVID-19 surge combined with flu season. 

"Every child, especially this season, needs to be up-to-date on all their vaccines, getting their flu vaccine and especially getting their COVID vaccine," Romano advised. 

Fox News' Maria Paronich and Molly Line, as well as several Fox News affiliates, contributed reporting to this article.