Acute flaccid myelitis (AFM) typically spikes in the late summer to early fall "season," but federal health officials are already warning clinicians to be on high alert for the paralyzing disorder, which has struck 11 young children so far this year.
"I urge physicians to look for symptoms and report suspected cases so that we can accelerate efforts to address this serious illness," CDC Director Robert Redfield, MD, said in a news release.
"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," CDC Principal Deputy Director Anne Schuchat, MD, said during a press briefing.
Recognizing AFM is challenging, the CDC acknowledges. The condition is rare, and no diagnostic laboratory test is currently available. The main cause of the condition remains elusive. In the majority of cases, AFM patients are otherwise healthy young children who experience a mild respiratory illness or fever consistent with a viral infection. They then develop AFM.
The CDC began tracking AFM in 2014, when the first outbreak, involving 120 cases, occurred. Another outbreak, which involved 149 cases, occurred 2 years later, in 2016. An outbreak occurred again 2 years later, in 2018. That outbreak, which involved 233 cases in 41 states, has been the largest so far. In 2019, 11 confirmed cases have been reported in eight states; 57 cases are under investigation.
AFM has so far followed a seasonal and biennial pattern, with cases spiking between August and October every other year.
"The every-other-year pattern is intriguing," said Schuchat. The pattern points to viruses as a potential player, "but we cannot assume that it's a long-term pattern because we've really only been tracking this since 2014. But we want clinicians and parents to be ready for a possible significant outbreak this year."
"Delay Hampers Our Ability to Understand"
In a report published today, CDC researchers updated clinical, laboratory, and outcome data for the 233 confirmed cases that were reported to the CDC in 2018.
As in the first two outbreaks, the average age of AFM patients was about 5 years. Most had respiratory symptoms or fever within 4 weeks of developing limb weakness.
"Patients were severely affected by AFM," Tom Clark, MD, deputy director, Division of Viral Diseases, told the briefing; 98% of patients were hospitalized, 60% required care in the intensive care unit, and 27% required mechanical ventilation. "They quickly received medical care," he noted.
On average, patients were hospitalized within 1 day after onset of limb weakness. Specimens were collected for testing within 2 to 7 days on average. However, suspected cases were reported to the CDC from 18 to 36 days after symptom onset. "This delay hampers our ability to understand the causes of AFM," said Clark.
In 44% of confirmed cases, laboratory testing revealed multiple enterovirus and rhinovirus types, primarily in respiratory and stool specimens. Virus types included enterovirus D68 (EV-D68) and enterovirus A71 (EV-A71).
Of the 74 cases for which a cerebral spinal fluid specimen was available, only two were found to be positive for enteroviruses — one with EV-A71, and one with EV-D68. No stool specimen tested positive for poliovirus, a related enterovirus that can cause AFM.
Since 2014, the CDC has tested spinal fluid of most patients with AFM. In only a few such tests has a pathogen been identified. "When a virus is found in the spinal fluid, this is good evidence that this is the cause of the patient's illness," said Clark.
The CDC is continuing to monitor AFM trends and clinical presentations. They are conducting research to identify possible risk factors, using advanced laboratory testing and research to understand how viral infections may lead to AFM. They are also tracking long-term outcomes of AFM patients.
Clark noted that since the first outbreak in 2014, 70% to 80% or more of children with AFM have experienced ongoing limb weakness several months after the onset of symptoms. There is some evidence that "early and aggressive rehabilitation" is helpful, he said. The CDC has published interim considerations for clinical management on its website.
