By Jamie Ducharme
Updated: January 23, 2019 9:48 AM ET | Originally published: December 4, 2018

The Centers for Disease Control and Prevention (CDC) has confirmed a record number of cases of the rare, polio-like illness acute flaccid myelitis (AFM).

The agency has so far confirmed 201 cases in 40 states for 2018, topping the 149 recorded in 2016. The CDC put another 165 patients under investigation in connection with the disease, which typically strikes young children and results in muscle weakness and possible paralysis, respiratory failure and even death.

Despite those inflated numbers, the CDC announced in December that AFM cases had likely peaked for the year. The CDC said the rate of reported cases has slowed, and that it recently received increased reports of patients who became sick in August, September and October, suggesting that fewer new illnesses were emerging.

While there’s still a lot experts don’t know about AFM — including, most importantly, what causes it and how best to treat it — health officials have noted distinct seasonal patterns associated with the condition. Its case count has spiked every-other year since an outbreak in 2014, and in each of those years, the majority of cases were reported from August through October, before slowing significantly in November. The 2018 outbreak appeared to be in keeping with those trends.

The CDC in November assembled a task force of medical and public health officials to better understand the mysterious condition. That group may be especially crucial, given recent research findings around AFM.

In November, a small retrospective study found that what looked to be a promising treatment for AFM did not, in fact, significantly improve disease outcomes. And in December, a small paper published in JAMA Pediatrics found that about a fourth of 45 children who met the CDC’s criteria for AFM between 2012 and 2016 had alternate neurologic conditions, pointing to the difficulty of accurately diagnosing and assessing AFM.

Write to Jamie Ducharme at jamie.ducharme@time.com.

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