Researchers say as many as 25 children in California who have developed a mysterious polio-like illness since 2012.
Dr. Keith Van Haren at Lucile Packard Children's Hospital says, "it can affect one or more limbs, and the prognosis that we've seen so far is not good, most of the children we've seen have not recovered use of their arm or leg."
Some of the children first had symptoms of a cold. But health experts still don't know if the illness is caused by a virus or something else.
According to CBS News Medical Contributor Dr. Holly Phillips, "even though it's acting like polio, where the paralysis develops suddenly over 48 hours, it's definitely not polio. In fact, all of the children who have been confirmed to have the illness, were vaccinated against it and tested negative for it."
Doctors say the illness is serious, but very rare. Dr. Amesh Adalja, an emergency and infectious disease specialist at UPMC says "early evidence shows it is caused by virus related to polio." Dr. Adalja says he's never seen a case. But the enterovirus which apparently causes it, also leads to the common cold, and is everywhere.
"I would like to know what proportion of people that are infected with this virus get paralytic disease because just like in polio, it's likely to be a minority of patients that develop paralysis," he says. "Most people probably have a self-limited type of viral illness where they get sick for a couple of days, then they're better."
Dr. Adalja also calls the five confirmed cases and 20 probable cases in California, over two years, a trickle, not an outbreak.
In an interview with WTAJ, he said, "I don't think it's the start of anything. I think that enteroviruses are a very common class of viruses. Most people have been infected by them. What we're seeing is a rare complication of a specific enterovirus infection."
"The discovery of these cases really reinforces the fact that surveillance of infectious diseases and syndromes are really essential for us to assess what threats we face and how to combat them. The fact these cases were uncovered by doing meticulous review of cases of paralysis shows that actually chasing down mysterious illnesses and not allowing things to be settled without finding a definitive cause is the right way to go."
"I don't think this is something the general public should be worried about. These types of viruses are everywhere in the environment and they're actually not avoidable."