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Virus associated with polio-like muscle weakness is spreading among kids, CDC warns

The CDC has detected 260 cases of enterovirus D68, which most commonly leads to respiratory illness among kids but can also cause acute flaccid myelitis in rare cases.
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The Centers for Disease Control and Prevention is warning about the spread of a common childhood virus that can cause muscle weakness or paralysis in rare cases.

According to a report released Tuesday, the CDC recorded 260 cases of enterovirus D68, which most commonly leads to respiratory illness among kids, from March 1 to Sept. 20.

That's more than in the last three years combined. The CDC identified six cases in 2019, 30 in 2020 and 16 in 2021.

Kids who have gotten EV-D68 this year are under 3 years old, on average. Cases been detected across seven pediatric medical centers affiliated with the CDC’s New Vaccine Surveillance Network — in Nashville, Tennessee; Houston; Kansas City, Missouri; Cincinnati; Seattle; Pittsburgh; and Rochester, New York.

During the week of Aug. 8, 56% of children and adolescents who required emergency care or hospitalization for acute respiratory illness at those seven sites tested positive for EV-D68.

The enterovirus family is large, and polio falls within it; both EV-D68 and poliovirus can invade the nervous system and cause muscle weakness.

Occasionally, EV-D68 can result in a condition called acute flaccid myelitis, or AFM, which is characterized by inflammation in the neck region of the spinal cord. Some people who experience AFM have difficulty moving their arms, while others experience weakness in all four extremities.

During a large outbreak in the U.S. in 2014, around 10% of people diagnosed with EV-D68 went on to develop AFM, but the condition is likely rarer than that, since not everyone gets tested for EV-D68.

Full recovery from AFM is uncommon. Most patients improve to some extent, but the process is often difficult and requires rehabilitation.

As of Sept. 21, 15 cases of AFM had been confirmed this year across 10 states, according to the CDC. The agency is investigating 30 additional cases.

Why are EV-D68 cases rising this year?

In the past, the CDC has recorded spikes in EV-D68 cases every other year. Before the coronavirus pandemic, that was in 2014, 2016 and 2018. Dr. Benjamin Greenberg, a neurologist at UT Southwestern’s O’Donnell Brain Institute who treats patients at Children’s Health in Dallas, said the pattern most likely appears because kids develop immunity to the enterovirus when it spreads, leading to "off" years with higher population immunity. Once the immunity wanes, case numbers tick up again.

Dr. Sarah Hopkins, a pediatric neurologist at Children’s Hospital of Philadelphia, said experts thought there would be a spike in 2020, following the pattern.

"But then with mask-wearing and social distancing and all those things that limit the spread of a respiratory virus, we didn’t have that expected spike," she said.

Greenberg said cases are most likely rising again this year because children are back in school and other public spaces.

"We have a group of kids now who’ve never seen the virus, because they weren’t having school exposures. So we think the at-risk population is bigger than in 2020," he said.

The CDC is asking health care providers to be on the lookout for EV-D68 cases among kids and to strongly consider AFM as a potential diagnosis for patients with limb weakness.

But it can be hard to distinguish EV-D68 symptoms from those of other respiratory viruses, Greenberg said. Like the common cold, EV-D68 can cause a runny nose, sneezing, body aches or muscle aches. Children who require hospitalization tend to have coughs, shortness of breath, wheezing and — in about half of cases — fever.

The most common symptoms among this year's EV-D68 cases so far have been shortness of breath or rapid shallow breathing, wheezing, cough and nasal congestion, according to the CDC.

AFM could also be confused with a severe case of polio, which results in a similar condition called acute flaccid paralysis. The U.S. recorded one polio case in July, and it has detected the virus in wastewater across several New York counties.

Greenberg said the polio detection calls for "raised awareness among health care providers so that they can send appropriate testing."

"It’s really important to know which virus is causing the paralysis in patients,” he added.

What is enterovirus D68?

Scientists first identified enterovirus D68 in 1962. At the time, the virus wasn't circulating much, and it resulted in milder illness than it does today, Greenberg said.

The CDC started doing more testing for EV-D68 in 2014, when scientists noticed a shift in how the virus behaved.

"The virus changed over time in order to acquire the ability to kill neurons to damage the spinal cord," Greenberg said.

This year's case total is lower than 2018's. From July to November of that year, the U.S. had 382 cases of EV-D68 among children with acute respiratory illness.

"I’m hopeful that at least there’s not a tidal wave of new neurologic cases as of yet," said Dr. Keith Van Haren, an assistant neurology professor at Stanford University.

But the CDC report suggested that health care facilities prepare for an increase in severe illnesses associated with EV-D68. Most EV-D68 cases happen around this time of year, from August to November, Van Haren said, and it takes one to four weeks for an EV-D68 case to progress to AFM.

"The outcomes are everything from just a little bit of slight shoulder weakness to difficulty moving all extremities and sometimes even needing prolonged respiratory support," Hopkins said.

Patients usually start to recover from their respiratory symptoms before neurologic symptoms set in, according to Van Haren.  

"When the neurologic symptoms begin, they can begin pretty suddenly. They can peak within the course of hours in a way that can be a little bit startling," he said.

Children who develop AFM usually require hospitalization. For reasons scientists haven’t quite figured out, kids at greatest risk include those with histories of asthma.

There are no specific treatments for AFM. Doctors may provide antibody therapy to improve a patient’s immune response or administer supportive care, like ventilators or fluids.

The best way to protect yourself or your kids from EV-D68, experts said, is to be diligent about hand-washing and to wear a mask in public.