Officials from Maine’s largest health care networks are warning that the surge in respiratory infections in children, especially of the highly common respiratory syncytial virus, or RSV, is pushing hospitals to  capacity.

“RSV, first of all, is one of the most common childhood illnesses,” Dr. Joe Anderson, a pediatric hospitalist at Central Maine Medical Center in Lewiston, said this week.

“Almost all kids get it by the time they’re 2 years old,” and some do get sick enough that they need to go to an emergency room or admitted to a hospital, he said.

But so far this year, RSV infections among children have exploded and more children end up in an emergency department or admitted for care, Dr. Jonathan Wood, a pediatric intensivist at Eastern Maine Medical Center in Bangor, said Friday at a joint news conference with leaders from MaineHealth and Northern Light Health.

“We are seeing numbers like we’ve not seen in quite a number of years,” Wood said.

It’s not yet clear if the virus itself is more severe, “but I do believe that the numbers are extraordinary,” he said.

It’s also not yet clear why RSV is circulating so highly this year, or why cases are popping up much earlier in the cold and flu season than usual.

Anderson said it’s highly unusual to see any RSV cases from May until October. In the Northeast, cases typically reach a peak in January.

But about a month ago, cases began to spike among children under the age of 5.

“And that’s probably got to do with the fact that it hasn’t circulated much in the last three years,” Dr. Dora Anne Mills, the chief health improvement officer for MaineHealth, said at the Friday conference.

“And it’s not because we were all wearing masks because COVID circulated the last two and a half to three years,” she said. Rather, it’s likely because COVID “crowded it out” and because a lot of children under the age of 5 haven’t gotten it before.

Plus, “the spike is bigger than what we usually have. It’s the biggest that most of us have seen,” Anderson said. “And it’s really starting to overwhelm pediatric floors and pediatric hospitals.”

The pediatric inpatient floor at CMMC typically hovers around 10 beds, though it can fluctuate based on need. CMMC has so far mostly been spared from a huge influx of pediatric patients with RSV — but only because the children who are admitted require an intensive level of care that CMMC does not offer, Dr. John Alexander, Central Maine Healthcare’s chief medical officer, said Friday afternoon.

“Luckily, we haven’t seen that many cases yet. But that is the big difference, that, you know, we haven’t really had a challenge in terms of our inpatient units simply because the severity of illness in these children warrants a higher level of care,” Alexander said.

The same has been true for Lewiston’s other hospital, St. Mary’s Regional Medical Center. The hospital does not have a dedicated pediatric unit and instead, like CMMC, shares a floor with the adult inpatient unit, Dr. Douglas Smith, the chief medical officer, said Friday.

Also like CMMC, the more acute cases are transferred to a pediatric unit that can provide a higher level of care, typically Maine Medical Center in Portland or EMMC in Bangor.

“But we have been faced with some delays in terms of getting patients there simply because of the number of children requiring admission,” although delays are mostly limited to a number of hours, not days, Alexander said. CMMC has had to send some children to Boston Children’s Hospital.

Dr. James Jarvis, Northern Light Health’s COVID-19 response leader, repeated the challenge they’re facing in transporting patients.

“This is extremely important when we talk about children as there are a few hospitals that can take care of pediatric patients and even less beds for us to take care of those who are severely ill,” he said. “And so being able to transport them in a timely fashion is incredibly necessary but when our ambulances are going to so many different places, oftentimes it makes it difficult for us to manage that.”

On Friday, all 87 beds at Barbara Bush Children’s Hospital at Maine Medical Center in Portland were occupied,” MaineHealth officials said. Only one of EMMC’s 37 pediatric beds was open, Northern Light officials said. Both hospitals have had to keep some children in the emergency department.

“It’s kind of like a double-edged sword because while we want everyone to know how stretched the health care system is right now, we also don’t want parents to panic,” Dr. Mary Ottolini, the pediatrics chairperson at Barbara Bush Children’s Hospital, said.

This is a reminder to take preventative measures, such as keeping up to date on vaccinations, and taking other precautions, like staying home when sick or even reconsidering attending large holiday gatherings to protect vulnerable members of a household, the doctors said.

“I can’t reiterate this enough: It is important for those of us who are eligible to be vaccinated against influenza and COVID that we do so,” Jarvis of Northern Light Health said. “We cannot have an issue where we are seeing so many patients with influenza and COVID being admitted to our hospitals that we can’t care for our most vulnerable children who are infected with RSV or other respiratory viruses.”

“We need to keep our emergency rooms open for emergencies,” he said. “And we need to keep our hospital beds open for those who are in need. So please help us in limiting the spread of respiratory viruses.”