On Sunday night, 4-month-old Aesop Light was happy and alert. By Monday morning, he was struggling to breathe.
Aesop's parents, Corey and Tara Light, took him to an emergency room near their home in the Chicago suburbs, but it didn't have a children's wing, so Aesop was rushed by ambulance to another hospital an hour away. He tested positive for respiratory syncytial virus, or RSV, a common virus that causes lung infections.
Aesop's condition "went downhill really fast," Tara said.
Hospitals across the country have reported a surge in RSV cases over the last three to four weeks. The virus began circulating in the summer, to doctors' surprise, since it usually peaks in winter.
For many kids, RSV symptoms look like a common cold. But for others — young babies or children with lung diseases or weakened immune systems — symptoms can be more severe.
"The ones who tend to get the most sick are the infants below four months. And then the ones who are older who tend to get most sick are those who have some other medical conditions," said Dr. Sameer Kamath, chief medical officer for Duke Children's Hospital and Health Center.
RSV can lead to bronchiolitis, an infection that causes airways to become inflamed and clogged with mucus, making it difficult to breathe. If the infection travels to the lung sacs, it can result in pneumonia.
According to the Centers for Disease Control and Prevention, RSV results in around 58,000 annual hospitalizations and 100 to 300 deaths among children under 5.
Aesop was moved to a pediatric ICU on Tuesday after his heart and breathing rates soared. Tara has been staying with him in the hospital, since she still breastfeeds. Meanwhile, Corey has been driving back and forth to take care of their three other kids.
NBC News spoke with six doctors across five states — California, Illinois, Massachusetts, North Carolina and Rhode Island — all of whom said pediatric hospital bed capacity has been strained due to an influx of RSV patients.
"We're really having a capacity problem like I've never seen before," said Dr. Charlotte Boney, pediatrician-in-chief at Baystate Children's Hospital in Springfield, Massachusetts.
The CDC said it does not keep a national count of RSV cases, hospitalization or deaths, but it tracks changes in the virus' spread.
"We have observed a rise in RSV in multiple U.S. regions, and some regions are nearing seasonal peak levels," a CDC spokesperson said.
Last week, nearly 5,000 tests came back positive, according to CDC data. That's not far from the number in the same week of October 2021 but far higher than in October 2020.
Boney said her hospital experienced a higher volume of patients in September than ever recorded, many of whom had RSV. Her pediatric ICU was closed to new patients on Wednesday because no beds were available.
During a normal winter, her emergency room might see around 100 children a day, Boney said. It's now seeing about 130 to 150. Many RSV patients in Massachusetts are being transferred to nearby states, she added.
Dr. Michael Koster, director of pediatric infectious diseases at Hasbro Children's Hospital in Providence, Rhode Island, said his hospital has been treating some RSV patients from over 100 miles away.
Kamath said that in the area around Raleigh, Durham and Chapel Hill, "there have been nights when there has been one bed available between three institutions, which is very scary."
At Comer Children's Hospital in Chicago, hospital and ICU beds have been full for over a month. Dr. John Cunningham, the hospital's physician-in-chief, said the emergency room is seeing a 150% higher volume than its usual for October. He said the hospital is treating around 10 to 30 RSV patients at a given time, so they occupy a large share of its 30 ICU and 60 emergency beds.
Cunningham's hospital is directing some patients to other facilities, but it can take 24 hours for a transfer, and a child's condition could easily deteriorate in that time.
"Depending on the severity, it's not an exaggeration to say minutes, hours matter," said Dr. Benny Joyner, medical director of the pediatric ICU at UNC hospitals in Chapel Hill, North Carolina.
In San Diego, 50 patients have tested positive for RSV over the last few days at Rady Children's Hospital, according to Dr. John Bradley, the hospital's medical director of infectious diseases. He said the volume of RSV patients is "two to three times what we've ever experienced."
"In mid-October, an epidemic of RSV is basically unheard of in San Diego," Bradley added.
What a severe RSV case looks like
Doctors said RSV is spreading earlier this year and resulting in more severe illness in some kids because many children weren't exposed to respiratory viruses earlier in the pandemic due to masking and social distancing.
"All those infection control measures protected us from all these viruses. Now everyone has relaxed those measures and these viruses are back with a vengeance," Boney said.
Doctors said they've seen many young kids who contracted RSV from an older sibling, who in turn was infected at school or day care. That's how the Light family thinks Aesop got sick: They have a daughter in first grade, a son in pre-kindergarten and a 2-year-old daughter at home. The entire family had cold-like symptoms last week.
"It's very much a contact illness," Cunningham said. "Hand hygiene is really the key thing. The major way that it disperses is actually by direct contact, rather than by somebody coughing on you."
Doctors said parents shouldn't worry about every cough or runny nose, but they should look out for signs that a child is lethargic or breathing hard or fast.
"If your child, especially under the age of 2, is flaring the nostrils, grunting, head bobbing or you're seeing sucking in around the collarbones or ribs, that's much more concerning," Koster said.
Kamath said many children who show up to the hospital aren't able to eat or drink because they're breathing so rapidly. If your child can't consume liquids, Joyner said, "that's a harbinger that you need to bring them in and get them evaluated."
Aesop Light showed many of those warning signs, Corey said. Doctors told the Lights that their son needed oxygen support and tubes inserted into his nostrils to suction the mucus from his airways.
On Thursday, Aesop was finally able to breathe on his own.
Children hospitalized with RSV typically recover within two to three days, though "a small minority do end up in the ICU, and then sometimes even on the ventilator," Kamath said.
ICU patients tend to recover within a week, according to Joyner.
RSV vaccines and treatments are on the horizon
Aside from breathing tubes, ventilators and supportive care like steroids or fluids, doctors don't have many ways to treat RSV.
"There is no Paxlovid-like drug for RSV. There is no Tamiflu drug like we have for influenza," Boney said.
One drug, a monoclonal antibody called Synagis, is approved for babies at high risk of severe RSV, such as those born premature or with chronic heart or lung problems. But doctors said they give that treatment sparingly.
However, Bradley said his San Diego hospital is set to participate in a clinical trial of an RSV antiviral from Pfizer later this year.
"I've already told Pfizer, 'Hurry up, get the study up and running,'" he said. "We're being overwhelmed with RSV, so it'd be easy to study the drug right now."
Pfizer is also testing an RSV vaccine candidate, which was found to be nearly 86% effective in preventing severe illness in a late-stage trial of older adults. Another RSV vaccine candidate, from pharmaceutical company GSK, was found to be around 94% effective against severe disease among adults ages 60 and up, according to data released Thursday.
Bradley predicted it will like take another few years for an RSV vaccine to become available. In the meantime, he said, oxygen support is highly effective.
"It's purely a lung infection. This virus doesn't go anywhere else in the body the way influenza does," he said, adding that "once they get oxygen and the lungs work, the kids actually feel OK."