The condition, called acute flaccid myelitis or AFM, has so far sickened 127 people, according to the Centers for Disease Control and Prevention. Of these cases, 62 have been confirmed in 22 states — and there appears to be no geographic clusters in the outbreak so far.
Since the CDC began tracking AFM in 2014, they’ve detected between 22 and 149 cases every year. But this year’s AFM outbreak is notable because there are 127 suspected cases so far — and we still have two-and-a-half months to go. The current number is also significantly higher than the 33 cases confirmed last year, and the CDC hasn’t been able to figure out what’s driving the uptick.
AFM affects the nervous system — specifically, the area of the spinal cord called gray matter — and causes muscle weakness and paralysis in the arms and legs. Sometimes these symptoms are temporary, sometimes they persist, and doctors don’t understand why or who is most at risk.
The condition can be brought on by viruses, including the enterovirus and West Nile, as well as environmental toxins, explained Dr. Nancy Messonnier, CDC’s National Center for Immunization and Respiratory Diseases, in a press briefing Tuesday. So people may become infected with these viruses or exposed to certain toxins, then experience the polio-like symptoms of AFM.
“We understand that people particularly parents are concerned about AFM,” she said. “I am frustrated that despite all of our efforts we haven’t been able to identify the cause of this mystery illness.”
That’s just one of the mysteries surrounding this year’s increase in cases. Here’s what we know and don’t know so far.
What we know
- Between August 2014 through September 2018, there were 386 confirmed cases of AFM across the US.
- In 2014, 2016, and this year, more people were sick with AFM than in 2015 and 2017 — but the trends are difficult to interpret since the CDC only began tracking AFM in 2014, and doctors aren’t required to report cases to the agency.
- The condition is rare, affecting less than one in a million people — even in years like this one, with more cases.
- Most of the patients are children under the age of 18, with the average age of 4 years old.
- Common symptoms include sudden weakness and loss of muscle tone in your arms or legs, as well as difficulty swallowing, facial or eyelid drooping, and slurred speech.
- All of the AFM cases so far have tested negative for poliovirus.
- The last major uptick in AFM cases happened in 2014 and coincided with an outbreak of enterovirus D68 (EV-D68). A respiratory illness, it spreads from person to person by coughing or sneezing, and typically manifests with cold-like symptoms — but can also lead to sudden paralysis and infections in the heart and brain.
- One child died of AFM in 2017.
- Parents can protect their kids from serious illnesses like AFM by washing their hands, making sure vaccines are up to date, and using insect repellent to prevent mosquito bites.
What we don’t know
- Peaks of the disease happen every late summer and early fall — but health officials haven’t been able to figure out what’s causing the seasonal variation.
- In the past, rhinovirus and enterovirus have been culprits. This year, they’ve ruled out poliovirus.
- They don’t know who is at higher risk of AFM.
- There’s no particular treatment for the conditon.
- The specific course of illness isn’t clear, either. As Messonnier said, “We know that some patients diagnosed with AFM have recovered quickly and some continue to have paralysis and require ongoing care.”
- It’s not clear if certain parts of the country are most at risk, since AFM has been reported in many states with no state being particularly hard hit.
- Whether the outbreaks are related to the anti-vaccine movement is also unclear.