A rare neurological condition that mostly affects children and mysteriously returns every two years is likely to flare up in the coming weeks and months, US health authorities warned Tuesday.

The US Centers for Disease Control and Prevention said that it "anticipates that 2020 will be another peak year for cases of acute flaccid myelitis (AFM)."

The disease, which is likely caused by a virus, can lead to permanent paralysis and life-threatening complications from respiratory failure, the CDC said.

"AFM is a medical emergency that requires immediate medical care and monitoring, as this condition can progress rapidly to respiratory failure," CDC Director Robert Redfield said Tuesday in a call with journalists.

He warned parents not to hesitate to hospitalize their child despite the COVID-19 pandemic if they show symptoms.

Most patients develop sudden arm or leg weakness, with the disease affecting the nervous system, specifically the area of the spinal cord called the gray matter, he said.

AFM has peaked every two years from August to November since 2014. In 2018, 238 cases were identified in the United States, with patients having an average age of five.

Doctors remain fairly helpless to treat the disease, which can cause paralysis within hours or days and has no known treatment.

"Unfortunately, many kids with AFM will have permanent disability," said Thomas Clark, pediatrician and CDC deputy director of viral diseases.

"It's really important that kids get into rehabilitation" such as aggressive physical therapy and occupational therapy, he added.

Authorities are recontacting the families of children who contracted AFM in 2018 to find out how the disease has progressed as well as details on their current state of paralysis.

Early AFM warning signs include fever and respiratory symptoms, and after six days, weakness of arms and legs sometimes accompanied by gait difficulty, neck or back pain, and limb pain, according to a study of 2018 cases.

In addition to permanent paralysis, AFM can also cause serious respiratory complications, with nearly a quarter of patients needing mechanical ventilation for help breathing.

Enteroviruses are the main suspect for the cause of AFM, particularly enterovirus-D68, which was found in about 30 patients.

CDC experts however said they could not rule out the involvement of other viruses in the disease.

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