Why has October been so bad for a virus known as RSV?

October is usually a quiet month for Dr. Julie Kim and her colleagues at their pediatrics practice in Los Gatos, after the summer rush for physicals.

But this October? “It’s just crazy,” she said. “We’re double capacity.”

The main culprit is a respiratory bug known as RSV that can be especially difficult on infants and young children, and is responsible for a rise in pediatric hospital visits across the country. Kim said she has been seeing up to 50 kids in a day for a range of respiratory illnesses, but especially RSV.

And while the virus usually ramps up during the heart of the winter, “this year it is coming abnormally early, hitting health care systems and hospitals hard,” said Dr. Peter Chin-Hong, a UCSF professor of medicine who specializes in infectious diseases.

With COVID-19 precautions relaxed this year, young children who haven’t been exposed to RSV in recent years are being exposed now and getting infected in high numbers. And with influenza and new COVID variants lurking, experts say infection dangers could be even worse in the months to come.

RSV, or respiratory syncytial virus infection, often presents as a common cold in adults and older children but can be extremely dangerous for infants and young children, especially medically vulnerable ones. The symptoms can be similar to other viral diseases, so the only way to know for sure whether your child is suffering from the flu, a cold, COVID or RSV is to get tested, experts say.

RSV is a well-known threat in the world of pediatrics, but even pediatricians are surprised by the severity of this recent outbreak.

Kim says there are several factors at play, but she is concerned some of the worst outcomes she’s seeing now could be the downstream consequences of previous COVID infections, even ones that may have seemed mild at the time. “I have to think there’s a correlation,” Kim said. “Kids are recovering from COVID infections and then they get another virus on top of it.”

She said it is normal for a particularly bad RSV season to follow a light season, but that by any standard this year’s RSV outbreak is remarkable.

While most kids recover just fine, hospitalization is sometimes required. According to data from the CDC, the overall weekly hospitalization rate for RSV nationwide reached 2.2 per 100,000 the week ending Oct. 15, more than it’s been in October in recent years. For infants under 6 months, the rate reached nearly 100 per 100,000.

In the year before the pandemic, 11 children died in California from RSV. In 2020, the first year of the pandemic, only one child died from RSV, which spread much less that year because schools were closed and social distancing and masking prevented the spread of all respiratory viruses.

This year, just three weeks into the season, one child in California has died from RSV, and there have been 59 non-ICU hospitalizations and 17 ICU admissions, mostly among children, according to the California Department of Public Health’s weekly respiratory virus report.

And the data show the positivity rate for RSV specimens, a proxy for RSV activity, has reached 15.3% in the week ending on Oct. 22, the highest it has been at this point in the year in at least the past five years.

If a child is sick with RSV, parents should watch out for difficulty breathing and dehydration and should seek medical care if they notice signs of either.

“Particularly for infants, parents can watch for danger signs like nasal flaring, wheezing,” Chin-Hong said. “That means they’re having problems breathing.”

With severe RSV infections, children sometimes need to have their airways cleared of excess mucus and phlegm.

Niko Lecco, 32, who lives in Pleasanton, feels like his family’s experience this month with RSV was mild, compared to other stories he’s heard. His 3-year-old and 8-month-old daughters both had high fevers and had to go to urgent care several times over the past two weeks. His wife was also diagnosed with the virus, although her symptoms were mild. Their younger child was the sickest.

The symptoms they noticed? “Some labored breathing, fevers, lots of coughing, and congestion,” he said.

So what can parents do to help keep their kids and others safe and healthy?

“If your kids are sick, don’t send them to school, don’t send them to day care,” said Kim. “It’s just common sense.”