Since last summer, public-health officials have been trying to figure out why more than 100 children in dozens of states have suffered from a polio-like weakness in their limbs.

And while authorities have not found a direct link to the severe respiratory illness that affected children across the country last year, they are exploring whether that nationwide outbreak may be tied to this mysterious situation.

There have been 103 confirmed reports of children who have developed the illness, which is called “acute flaccid myelitis,” according to the Centers for Disease Control and Prevention. These cases, which span 34 states, have almost all led to the hospitalization of the affected children, with some of them put on breathing machines. 

Last fall, the CDC began testing cases that occurred after Aug. 1. They had tested 88 cases by mid-November and found some possible trends, but the ultimate cause of the illnesses were still unclear. A handful of cases involved children who had been affected by the enterovirus D68 outbreak, but the CDC cautioned that no causal relationship between the illness could be confirmed by that time. There are also other viruses that can cause illnesses with symptoms like the ones currently being seen, the CDC noted.

The possible tie to the enterovirus D68 (or EV-D68) outbreak is particularly worrisome, given how widespread this virus became. More than 1,100 people — again, most of them children — have been affected since last August. This number is likely severely underestimating how many were infected, as the CDC says there were presumably “millions” of mild infections in people who did not get tested. The virus was ultimately confirmed in 49 states and the District of Columbia.

In September, as the enterovirus outbreak continued, health officials in Colorado explored a cluster of nine children suffering from weakness and paralysis. Some of these children tested positive for the enterovirus.

Still, another concern in this latest illness is how many children have not seen any improvement since developing symptoms. Two out of three have said they had some improvement, compared to one in three who showed none. So far, only one child with the illness had fully recovered, the CDC says.

Nearly a year ago, another polio-like illness may have affected up to 25 children in California, leading to some limb paralysis. Enterovirus D68, which at that time was still considered a rare virus and had not become as widespread as it was later in the year, was cited as one possible factor.