Number of Cases of Polio-Like Virus Spike in US Kids, CDC Says

Megan Brooks

October 16, 2018

There is growing concern about a spike in cases among US children of acute flaccid myelitis (AFM) — a rare condition that causes a polio-like paralysis characterized by sudden weakness or loss of muscle tone in the arms or legs.

As of October 16, the US Centers for Disease Control (CDC) has received reports of 127 patients under investigation for AFM in 22 states, of which 62 cases have been confirmed as AFM. The average age of confirmed cases is about 4 years old.

"The case count reported today is a substantially larger number than in previous months this year," Nancy Messonnier, MD, director of the CDC's National Center for Immunization and Respiratory Diseases, noted during a media briefing. "With enhanced efforts and working with state and local health departments and hospitals, we were able to confirm a number of new, suspected cases faster," she explained.

As of September 30, there were 38 confirmed AFM cases, as reported by Medscape Medical News.

Going forward, the CDC announced today that it will report updated case counts every Monday afternoon on their website.

The CDC has been actively investigating AFM, testing specimens, and monitoring the disease since 2014, when an increase in cases was first detected. In 2014, there were 120 confirmed cases in 34 states, and in 2016, 149 confirmed cases in 39 states.

So far, in 2018, said Messonnier, "we are generally on track to have the number of cases similar to what we saw in 2014 and 2016 but it would be premature to say that we are confident that we know what is going to happen because we are early in this." Based on previous years, as well as in 2018, most AFM cases occur in the late summer and fall.

Messonnier emphasized that AFM remains "incredibly rare. Overall, the rate over the years that it's been diagnosed since 2014 is less than one in 1 million."

Cause Remains a Mystery

Messonnier said it remains unclear what causes AFM. "We know that poliovirus is not the cause of these cases. CDC has tested every stool specimen from AFM patients. None of the specimens has tested positive for poliovirus," she said. AFM may be caused by other viruses, environmental toxins, or genetic disorders.

"There is a lot we don't know about AFM, and I am frustrated that despite all of our efforts we have not been able to identify a cause of this mystery illness," said Messonnier. "Despite extensive laboratory testing, we have not determined what pathogen or immune response causes the arm or leg weakness or paralysis in most of these patients. We don't know who may be at higher risk for developing AFM or the reasons why they may be at higher risk," she added.

"We also don't fully understand what the long-term consequences of AFM are or why some patients diagnosed with AFM have recovered quickly while others continue to have paralysis and require ongoing care," said Messonnier.

The CDC has developed a toolkit for healthcare professionals that includes information about AFM and instructions for reporting patients under investigation to the health department.

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