The "season" for a polio-like illness that mainly strikes children is about to begin, so public health officials sent out an early warning to doctors on Tuesday.
The largest recorded outbreak of acute flaccid myelitis (AFM) occurred last year, with the illness debilitating 233 people in 41 states across the nation, according to the U.S. Centers for Disease Control and Prevention.
AFM cases typically spike between August and October, so the CDC is alerting medical professionals around the United States.
"Doctors and other clinicians across the United States play a critical role," CDC Principal Deputy Director Dr. Anne Schuchat said during a media briefing Tuesday. "We ask for your help with early recognition of patients with AFM symptoms, prompt specimen collection for testing, and immediate reporting of suspected AFM cases to health departments," she added.
"When specimens are collected as soon as possible after symptom onset, we have a better chance of understanding the causes of AFM, these recurrent outbreaks, and developing a diagnostic test," Schuchat explained.
AFM is a rare but serious disease that attacks the spinal cord, causing the muscles and reflexes in the body to become weak.
The disease mainly affects the arms and legs, causing serious limb weakness, but it can endanger a person's ability to breathe by weakening the muscles of the respiratory system.
One out of four confirmed AFM patients in 2018 required respiratory support, and most often they were put on a ventilator, the CDC said.
The average age of a confirmed AFM patient in 2018 was 5, the CDC reported.
Currently, there are no proven ways to either treat or prevent AFM. And at least half of patients do not recover from the illness, CDC officials have said. Officials continue to track the long-term progress of patients.
The CDC began tracking AFM in 2014, following an initial outbreak of 120 cases.
The disease has since settled into an every-other-year pattern, with major outbreaks recurring in 2016 and 2018. In 2016, 149 cases were reported.
All told, there have been 570 AFM cases in 48 states since 2014, the CDC said.
But Schuchat warned against complacency.
"I want to say that we cannot assume that it's a long-term pattern [outbreaks every other year], because we've really only been tracking this since 2014," she said. "We want clinicians and parents to be ready for a possible significant outbreak this year."
Experts aren't sure what causes AFM, but they are beginning to suspect that viruses might play a role, the agency noted. In nine out of 10 cases in 2018, respiratory symptoms or fever consistent with a viral infection preceded the onset of limb weakness.
The CDC detected enteroviruses and rhinoviruses in nearly half of respiratory and stool specimens gathered from confirmed cases in the 2018 outbreak, the agency added.
Doctors are being urged to look for early signs of limb weakness, and to gather a wide array of samples from patients as soon as possible, the CDC said.
The U.S. Centers for Disease Control and Prevention has more about acute flaccid myelitis.