The Centers for Disease Control and Prevention this week issued a warning about a disease known as acute flaccid myelitis (AFM), an illness it says it knows very little about but can cause arm or leg weakness and paralysis, particularly in children. According to a Tuesday press briefing, there have been 62 confirmed cases across 22 states in 2018.
AFM is an extremely rare but serious disease that affects the nervous system and results in polio-like symptoms, though the CDC says that all confirmed cases of AFM have tested negative for poliovirus. One death of a child diagnosed with AFM occurred in 2017.
“AFM can be caused by other viruses, such as enterovirus and west nile virus, environmental toxins and a condition where the body’s immune system attacks and destroys body tissue that it mistakes for foreign material. While we know that these can cause AFM, we have not been able to find a cause for the majority of these AFM cases,” Nancy Messonnier, director of the National Center for Immunization and Respiratory Diseases, said during the media teleconference. “The reason why we don’t know about AFM—and I am frustrated that despite all of our efforts we haven’t been able to identify the cause of this mystery illness—we continue to investigate to better understand the clinical picture of AFM cases, risk factors and possible causes of the increase in cases.”
“Despite extensive laboratory testing, we have not determined what pathogen or immune response caused the arm or leg weakness and paralysis in most patients,” Messonnier added.
Messonnier said that the CDC has neither a clear idea of who might be at higher risk of developing the disease nor why. Additionally, it doesn’t know what long-term effects of the illness could look like. Ninety percent of people diagnosed with AFM are under 18, with the average age of children in confirmed cases being about 4.
The CDC began tracking the illness in 2014 and has seen a spike in reports in August and September every 2 years, according to data on its website. It has received 127 reports of patients under investigation (PUIs) for AFM this year, though it notes that figure includes the 62 confirmed cases. The CDC received reports of 33 confirmed cases of AFM across 16 states in 2017, down from 149 confirmed cases in 39 states in 2016. In total, there have been 386 confirmed cases since 2014.
Despite the recent spike in reported cases of AFM, Messonnier underscored that the disease is “incredibly rare” and has been diagnosed annually at a rate of less than one in a million since 2014.
“Parents need to know that AFM is very rare, even with the increase in cases that we are seeing now,” Messonnier said. “We recommend seeking medical care right away if you or your child develop sudden weakness of the arms or legs. As we work to better understand what is causing AFM, parents can help protect their children from serious diseases by following prevention steps like washing their hands, staying up to date on recommended immunizations and using insect repellent.”