The United States is witnessing a surge in respiratory illnesses among children which has led to a strain on hospitals in several states as they continue to tackle new patients.

Cases of the respiratory syncytial virus, or RSV – a common cold virus associated with severe disease in young children and older adults – have spiked, according to the latest real-time surveillance data from the US Centers for Disease Control and Prevention (CDC).

The data shows that cases detected by PCR (polymerase chain reaction) tests have more than tripled in the past two months. Cases have spiked, especially in the Northeast and South.

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“RSV admissions have skyrocketed at Connecticut Children’s. October has been like never before for this virus,” Monica M. Buchanan, senior director of strategic and enterprise communications for Connecticut Children’s Hospital, told CNN.

Dr. Juan Salazar, executive vice president and physician-in-chief at Connecticut Children’s, told CNN’s Kate Bolduan that beds are filled to capacity.

“I’ve been doing this for a long time, I’ve been at Connecticut Children’s for 25 years, and I have never seen this level of surge – specifically of RSV – coming into our hospital,” he said.

However, hospitals are yet to expand to a field tent, “but we have to be prepared in case the numbers continue to increase. So if RSV increases further and it hits us with influenza at the tail end of this … we will need additional capacity for our hospital.”

“Why so much in September and October? We don’t know,” Salazar said. “We have theories: herd immunity, immune suppression, and everyone getting it at the same time — it’s the perfect storm at our emergency departments.”

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At Yale New Haven Children’s Hospital, RSV cases in the emergency department nearly doubled in the last week. Thirty children are admitted every day.

RSV in the US typically circulates during fall, winter and spring. However, this year, the cases have gone up earlier than doctors expected.

“We used to have kind of a seasonality to different viruses,” Dr. Thomas Murray, a pediatric infectious disease specialist and associate professor at Yale University School of Medicine, told CNN affiliate WFSB. “Like the one right now, respiratory syncytial virus or RSV would come in December, it would go away followed by influenza, it would go away and another one. What seemed to happen with Covid is that now they’re all circulating at the same time.”

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The CDC recommended that everyone age 6 months and older get a flu vaccine.

“Here we are in the middle of October – not the middle of November – we’re already seeing scattered influenza cases, even hospitalized influenza cases, around the country,” Dr. William Schaffner told CNN.