Toronto's Hospital for Sick Children has now identified six children with unexplained muscle weakness, one of whom has tested positive for enterovirus D-68, a previously rare strain of virus that doctors across North America are investigating as a possible cause of several clusters of partial paralysis in children.
Two of the six children have tested negative for enteroviruses. One has tested positive for rhinovirus. Test results are pending for the last two.
The results so far at SickKids mirror what hospitals and public health authorities elsewhere in Canada and the United States have found after testing young patients with sudden and mysterious neurological problems. Some have EV-D68 and others do not, leaving doctors baffled as to the cause of symptoms that in some cases have been likened to polio.
"I think, to be honest, at the moment it's pretty early in this whole scheme of things to really have a full understanding," said Jeremy Friedman, the associate pediatrician-in-chief at SickKids. "So I think what's happening at the moment is all the centres across North America are closely collaborating and communicating and comparing results and trying to find the answer to that question."
British Columbia has reported two patients with unexplained neurological symptoms, both of whom tested positive for EV-D68. Alberta has identified four children with similar symptoms, two of whom have tested positive for EV-D68 and two negative. Four patients in Hamilton have muscle weakness, one of whom has tested positive for EV-D68.
Dr. Friedman would not share details of the cases in Toronto, citing patient confidentiality. But he said all the children are under the age of 10. Their symptoms range from muscle weakness in a single limb to partial paralysis and some have recovered enough to leave hospital, Dr. Friedman added.
There are more than 100 serotypes of enterovirus, including polio. Until this year, EV-D68, which was first identified in California in 1962, was considered rare. It is difficult to say exactly how rare because doctors usually see no need to identify precisely what strain of virus is behind common cold symptoms, especially since there is no vaccine or anti-viral treatment for EV-D68.
SickKids, like other hospitals that have seen a spike in the number of children with severe respiratory issues or muscle weakness, started testing for EV-D68 in some patients in August. The hospital has diagnosed seven children with the strain so far, including the one with muscle weakness.
Late this summer and early fall, waves of children in the U.S. midwest began showing up to hospitals with severe respiratory illnesses that sent some to intensive care units. EV-D68 was linked to those serious respiratory problems, which proved worse in children with pre-existing problems like asthma.
Dr. Friedman said parents should not be too worried.
"Certainly we know that enterovirus D-68 in the vast majority of children is a very mild illness," he said. "Most children will just have some pretty mild cough and cold symptoms. So I don't see any reason for undue concern."