(CNN) Parents and pediatricians need to be on the lookout in the coming months for a rare, paralyzing condition that affects young children, the Centers for Disease Control and Prevention said Tuesday.
The polio-like condition, called acute flaccid myelitis or AFM, tends to peak every other year, and the last surge of cases was in 2018, when 238 cases were diagnosed across the US, the CDC said.
This year is likely to see another upsurge but things will be complicated by the coronavirus pandemic.
"AFM is a priority for CDC as we prepare for a possible outbreak this year," Dr. Thomas Clark, deputy director of CDC's Division of Viral Diseases, told reporters.
"We are concerned that, in the midst of a Covid pandemic, that cases might not be recognized as AFM, or we are concerned that parents might be worried about taking their child to the doctor if they develop something as serious as limb weakness," Clark added.
The CDC released results of a study done after the last outbreak in 2018. It put almost all the affected children into the hospital. Patients were 5 years old on average.
Most had a fever, respiratory illness or both a few days before they started showing the muscle weakness that is the most telling symptom of AFM.
"In addition to weakness, common symptoms at clinical evaluation were gait difficulty (52%), neck or back pain (47%), fever (35%), and limb pain (34%)," the CDC said in its report.
"Overall, 98% of patients were hospitalized, 54% were admitted to an intensive care unit, and 23% required endotracheal intubation and mechanical ventilation."
The CDC is following up with families now to see how the children have fared in the two years since they were affected. Some may be permanently affected, the CDC said.
Clark said parents and doctors need to act quickly if children show any symptoms of limb weakness or pain after an infection and should not hesitate to get them to the hospital, even in the middle of the coronavirus pandemic. An evaluation can tell doctors if AFM is possible and quicker treatment might help children recover better, the CDC said.
"Enteroviruses, particularly EV-D68, are likely responsible for the increase in cases every two years since 2014. AFM is a medical emergency and patients must be hospitalized and monitored in case they progress to respiratory failure," the CDC said.
Another virus called EV-A71 is also suspected of causing some cases of AFM. "Multiple viruses, including West Nile virus, adenovirus, and nonpolio enteroviruses, are known to cause AFM in a small percentage of infected persons," the CDC said.
Enteroviruses are common. They cause about 10 million to 15 million infections a year in the United States, according to the CDC. Although they're around all year long, they're most common in the summer and fall, which is also when AFM peaks.
Typically, enteroviruses cause cold-like symptoms such as fever, runny nose and body aches, and people recover easily.
"We don't yet know why certain kids develop AFM when the great majority who have a respiratory illness recover without neurological symptoms," Clark said.
Dr. Robert Redfield, the CDC's director, said his agency is watching to see how the coronavirus pandemic will affect the expected circulation of the viruses linked with AFM.
"It is not known how the COVID-19 pandemic and the social distancing measures may affect the circulation of viruses that can cause AFM, or if COVID-19 will impact the health care system's ability to promptly recognize and respond to AFM," Redfield said in a statement.
"If social distancing measures decrease circulation of enteroviruses this year, AFM cases may be fewer than expected or the outbreak may be delayed."
But he said parents need to be alert.
As the parent of six children and grandparent of 11, Redfield said he understands the instinct to hope symptoms just go away on their own. But limb weakness should be taken seriously. "We want parents to realize it is a potentially serious sign," Redfield told the briefing.
Whatever parents do to reduce the risk of coronavirus infection will also help prevent the infections linked with AFM, the CDC said. That includes careful hand hygiene, cleaning surfaces, mask use and physical distancing.
Acute flaccid myelitis first started causing concern in 2014, when it was diagnosed in 120 patients in 34 states. Since then, the number of cases has risen in an every-other-year pattern. The CDC confirmed 22 cases in 2015, 149 cases in 2016, 35 cases in 2017 and 238 in 2018.