Acute flaccid myelitis (AFM) has stricken 90 patients in the United States this year and another 252 cases are being investigated, according to new data from the Centers for Disease Control and Prevention.
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The number of confirmed cases is triple that seen in 2017.
Nearly all of the patients (90%) were children aged 2-8 years, and 99% experienced a fever and /or respiratory illness 7-10 days before the onset of symptoms. But although the prodrome and seasonality of AFM suggest an infective process, only 54% of the patients tested positive for the virus, Nancy Messonnier, MD, said during a briefing held by CDC officials. The most common findings were the enteroviruses EV-A71 (29%) and EV-D68 (37%); other viruses were recovered in the remaining pathogen-positive cases.
It’s not at all clear that these were causative agents, said Dr. Messonnier, director of the National Center for Immunization and Respiratory Diseases.
“At this time of year lots of children have a fever and respiratory infections,” she said. AFM may be caused by one of the identified viruses, a still-undetected pathogen, or a pathogen hiding in untested tissue. “Or, it could be an infection that’s kicking off an immune process,” attacking gray matter in the spinal cord.
The reported increase in cases must be viewed cautiously, Dr. Messonnier said. Physicians are becoming more aware of AFM, so the spike could represent an increase in reporting as well as actual incidence.
It’s not clear why the disease manifests almost exclusively in children, Dr. Messonnier said. Nor do health officials have much of a grasp on AFM’s long-term sequelae.
“We know that patients can recover fully, but at least half don’t, and some of those have serious sequelae. Unfortunately, we have not been following every patient, so this is a gap in our knowledge.”
A newly created national task force will examine AFM’s long-term effects, Dr. Messonnier said. The task force will also look at mortality; health departments across the country will examine mortality records to identify any past deaths preceded by AFM-like symptoms.
“One of the reasons we have convened this task force is to think about this hypothesis [of an autoimmune syndrome]. We have not backed off on the idea of an infectious organism causing it, but we are thinking more broadly,” Dr. Messonnier said.
Some anti-immunization groups are blaming vaccines for the disease, noting that several childhood vaccines list encephalomyelitis and transverse myelitis as possible adverse events.
“We are investigating every one of the cases in this and prior years and have a list of hypotheses based on the epidemiology,” Dr. Messonnier said. “I would say toxins are low on that list. Many of the children may have been vaccinated [before developing AFM] and that is something we will look at, but for now we recommend that all children should be vaccinated” according to the recommended schedule.
Additional details were published on 80 of the cases. Patients’ mean age was 4 years; 59% were male. Symptoms suggesting a viral illness occurred in 99%; these included fever (81%), cough, rhinorrhea, and congestion (78%), and vomiting and diarrhea (38%).
AFM symptoms varied; 47% had only upper limb involvement, 9% only lower limb, 15% two or three upper, and 29% all four limbs. All the patients with confirmed AFM were hospitalized, and 59% treated in intensive care units. There were no deaths (MMWR. 2018;ePub:13 November. DOI: http://dx.doi.org/10.15585/mmwr.mm6745e1).
AFM remains extremely rare, Dr. Messonnier said. But physicians should be alert for any signs of sudden limb weakness in children and report those immediately. The workup should include questions about recent fever with or without respiratory or gastrointestinal symptoms. Prompt collection of viral testing samples (cerebrospinal fluid, serum, respiratory, and stool specimens) is critical.
Additional information for health care professionals is available on the CDC AFM web page.