Cases have increased since 2014, mostly among children. 

By Amanda MacMillan
November 14, 2018

The U.S. Centers for Disease Control and Prevention (CDC) has received an unusually large number of reports of polio-like illnesses in people—mostly children—across the United States in recent months, according to an agency telebriefing held yesterday. So far in 2018, 90 cases of the rare disease, called acute flaccid myelitis (AFM), have been confirmed in 27 states, with an additional 252 reports currently under investigation.

AFM is a serious condition that affects the nervous system, causing sudden weakness, and sometimes pain or paralysis, in the arms and legs. It can also cause drooping eyelids, slurred speech, and difficulty swallowing. In recent weeks, news reports and home videos of children afflicted with these symptoms have circulated online, adding to the country’s growing concern.

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“We know this can be frightening for parents,” said Nancy Messonnier, MD, director of the CDC’s National Center for Immunization and Respiratory Diseases, said in a briefing in October. “I know many parents want to know what the signs and symptoms are that they should be looking for in their child.” Here are a few takeaways about AFM, including what to look for and how worried experts really are.

AFM has been on the rise since 2014

Dr. Messonnier said that the CDC has been testing for and monitoring reports of AFM since 2014, when an increase in cases was first noted. Since that time, most confirmed AFM cases have been among children.

Among AFM patients confirmed so far this year, the average age is 4. More than 90% of cases have been in patients 18 and younger. Often, patients experience a mild illness—which can include a fever, headache, and stiff neck—before developing a sudden onset of muscle weakness.

Most cases occur around this time of year

Based on previous years’ reporting, AFM strikes most patients in late summer and fall. This year is no different: “The data we are reporting today is a substantially larger number than in previous months this year,” said Dr. Messonnier, due to an increase in reports of patients whose symptoms started in August and September.

That doesn’t mean that we’re in the midst of an unprecedented outbreak, however. “The number of cases reported in this time period in 2018 is similar to what was reported in the fall of 2014 and 2016,” Dr. Messonnier said, although she added later that it's still too early to know how this year will ultimately measure up. It’s not unheard of for a number of cases to be reported all at once, either: In 2016, eight children were diagnosed with the condition in Washington State within the same week.

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The cause is unknown, but it’s definitely not polio

The CDC has tested stool samples from every confirmed AMF patient, and none have tested positive for poliovirus. Other viruses (like enterovirus, rhinovirus, and West Nile virus) and environmental toxins can cause AFM, but so far the CDC has not been able to identify a cause for most of the cases diagnosed this year. “[I]f you are having the peaks of disease every late summer and early fall, you would think we are finding a single agent,” Dr. Messionnier explained. “That is what we are not finding.”

Dr. Messonnier also said that she's frustrated “that despite all of our efforts we haven’t been able to identify the cause of this mystery illness." The CDC is continuing to investigate these illnesses, she added, to better understand its risk factors and possible causes of the increase in recent years.

Since the October briefing, the CDC has begun to suspect a virus is causing AFM. "Clinical, laboratory, and epidemiologic evidence to date suggest a viral association," according to a November 13 Morbidity and Mortality Weekly Report. 

Some patients recover quickly, while others have long-term damage

“We don’t fully understand the long-term consequences of AFM,” Dr. Messonnier said. “We know that some patients diagnosed with AFM have recovered quickly and some continue to have paralysis and require ongoing care.” In the most serious cases of AFM, patients can experience respiratory failure when the muscles that affect breathing become weakened. In 2017, one child died from AFM.

There is no specific treatment for AFM, but doctors may prescribe immunosuppressant drugs, steroids, and blood-replacement procedures. They may also recommend physical or occupational therapy to help patients get their strength and mobility back after experiencing muscle weakness or paralysis.

Parents shouldn’t freak out—but they should take basic precautions

“Parents need to know that AFM is very rare, even with the increase in cases that we are seeing now,” said Dr. Messonnier. (Overall, since 2014, the risk of developing the illness is less than one in a million.) Nevertheless, she added, “we recommend seeking medical care right away if you or your child develop sudden weakness of the arms or legs.”

Until more is understood about what’s causing these cases, Dr. Messonnier said in October that parents can help protect their children from pathogens by washing their hands and staying up to date on vaccines. "As a mom, I know what it’s like to be scared for your child, and I understand parents want answers," she said in yesterday's briefing. "CDC is a science-driven agency.  Right now the science doesn’t give us an answer.  That’s why we at CDC, along with all our partners, will keep looking for answers."

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