(CNN) Researchers found evidence of what might cause acute flaccid myelitis, known as AFM, a rare polio-like illness that affects children. According to a study published Monday in the journal Nature Medicine, a virus seems to be the culprit.

Since the first cases were documented in 2012, scientists have debated how children get AFM, which can cause weakness and paralysis. Some thought the cause was an autoimmune disorder, while others suspected a virus. Until recently, evidence of a virus was only circumstantial and couldn't be found in 98% of AFM patients who had their spinal fluid tested, according to the study.

Using a virus hunting tool called VirScan, scientists were able to examine the spinal fluid of patients for an immune response to enterovirus and to thousands of other viruses simultaneously. Using this method, the team confirmed the presence of antibodies for enterovirus strains D68 and A71 in nearly 70% of the 42 AFM patients that they tested. They did not find antibodies against any other virus.

"When there's an infection in the spinal cord, antibody-making immune cells travel there and make more antibodies. We think finding antibodies against enterovirus in the spinal fluid of AFM patients means the virus really does go to the spinal cord. This helps us lay the blame on these viruses," Dr. Ryan Schubert, a clinical fellow in neurology at the University of California, San Francisco and an author of the new study, said in an emailed statement.

Enteroviruses are common; they cause about 10 million to 15 million infections a year in the United States, according to the US Centers for Disease Control and Prevention. Typically, enteroviruses cause cold-like symptoms such as fever, runny nose and body aches, and recovery is easy.