Medical researchers across the country have formed an informal network to figure out what's causing an outbreak of acute flaccid myelitis (AFM) cases.

So far this year, state health departments have referred 155 potential AFM cases to the CDC.

AFM, a polio-like disease, can cause paralysis and mostly affects young children.

Doctors and researchers who have been treating patients with AFM say they believe a virus called EV-D68 may be responsible for the recent uptick in cases.

Doctors and medical researchers believe a relatively harmless virus is to blame for the recent outbreak of acute flaccid myelitis (AFM) cases in the United States, according to a new report from NBC News.

AFM is a disease that affects mostly young children, and causes polio-like symptoms. It usually starts with cold-like symptoms, and progresses to causing paralysis in the limbs. AFM can prove deadly if the patient loses the ability to breathe for themselves.

So far this year, state health departments have referred 155 potential AFM cases to the CDC, which has confirmed 62 of those cases so far.

While the CDC won't say what is causing the new outbreak, NBC News spoke to doctors and researchers treating patients, and they believe the uptick in cases is likely due to a virus called enterovirus D68, or EV-D68.

According to the CDC, EV-D68 is a non-polio enterovirus that commonly circulates around the US during summer and fall. EV-D68 usually causes mild symptoms including sneezing, a runny nose, cough, body aches, and muscle aches. In severe cases, it can cause respiratory issues.

The above graphic shows how AFM affects the nervous system. CDC

A reappearing issue

The first time that AFM caused a public concern was back in 2014, when there was an outbreak of 120 cases that coincided with an outbreak of EV-D68 as well.

Similar spikes in both have been seen about every two years since then, the experts told NBC.

While the CDC says there hasn't been enough evidence to link the two, the doctors interviewed say many of their AFM patients presented with EV-D68.

"It does seem that enterovirus D68 has been present every other year," Dr. Gregory Storch of Washington University in St. Louis told NBC. "Each of those times, there has been an increase in acute flaccid myelitis that occurred at the same time as the EV-D68 activity."

The number of Acute flaccid myelitis (AFM) appear to spike in August and September every two years, and researchers aren't sure why. CDC

Dr. Ken Tyler, a neurologist at the University of Colorado School of Medicine, says he and his colleagues have been studying the way EV-D68 affects mice, and found that it can impact the nervous system.

"We know that enterovirus D68 in mice can produce an illness very much like what you see in children," Tyler said. "You can see enterovirus particles in the motor neurons."

But Tyler admits that's still not enough to blame EV-D68 for this most recent AFM outbreak, and that more research needs to be done.

What this means for parents

Since AFM typically affects young children, with the average age of patients this year being 4, parents are being told to make sure their kids wash their hands frequently and to protect them from mosquito bites to lower the risk of spreading disease.

If their child starts to present with cold-like symptoms, parents should closely monitor their symptoms to see if they develop any paralysis. If they do, they should bring them to the hospital immediately.

While AFM doesn't have a cure, early detection appears to be helping children recover faster.