In his 16 years as a pediatric neurologist, Brandon Meaney has never seen a situation like the one unfolding now at McMaster Children's Hospital in Hamilton, Ont.
In the space of two weeks, four children have turned up with polio-like symptoms that doctors cannot explain. All have been vaccinated against polio and none had contact with each other before arriving at the hospital.
Although Dr. Meaney, the head of pediatric neurology at McMaster, said his hospital sees an average of four to six patients every year with sudden muscle weakness and partial paralysis, the cause of their illness is usually swiftly diagnosed as something like Guillain-Barré syndrome, an immune disorder.
"But the polio-like presentation?" he said. "I haven't seen a case in over 10 years."
So far this month, nine other cases of patients with similar polio-like symptoms have been reported elsewhere in Canada: two in British Columbia, four in the Calgary area and three at the Hospital for Sick Children in Toronto.
It's too early to determine the ultimate prognosis for these patients, though some have begun to recover the movement they had lost.
Dr. Meaney and his counterparts across Canada and the United States are trying to figure out if these cases of out-of-the-blue partial paralysis are caused by enterovirus D-68 [EV-D68], a previously rare strain of cold virus that has spread more widely in North America this year, causing severe respiratory illness in some children.
Clusters of children with unexplained neurological symptoms and sudden paralysis have also emerged in Colorado recently, and in California between June of 2012 and June of this year.
"There is a mystery here," Dr. Meaney said. "With all the darn cases and all the attention and the [U.S. Centers for Disease Control and Prevention] and everyone focused on it, we've got to at some point be able to pin it down."
Linking the muscle weakness and partial paralysis cases to EV-D68 is no straightfoward task. In B.C., the two afflicted patients have tested positive for EV-D68, but in Hamilton only one has. Two other Hamilton patients have tested negative for EV-D68, while tests on the fourth patient are pending. Results are also still pending for the three patients in Toronto and the four in Calgary.
Meanwhile, plenty of Canadian children have tested positive for EV-D68 late this summer and in early fall without developing any polio-like symptoms. Hamilton, for instance, has diagnosed 139 cases of EV-D68; Alberta has found 50 so far.
"Of those 50 cases none of the ones we've confirmed with EV-D68 have had any neurological issues," said Gerry Predy, senior medical officer of health for Alberta Health Services.
There are more than 100 types of enterovirus. Polio is one of them. However, the vast majority of enteroviruses cause symptoms no worse than the common cold.
EV-D68 was first identified in California in 1962. In the U.S., a national system for monitoring enteroviruses received only 79 reports of EV-D68 between 2009 and 2013. The Public Health Agency of Canada has confirmed 82 cases in the last decade, prior to the recent rash of cases.
Marek Smieja, an infectious diseases specialist and the head of virology at the Hamilton Regional Laboratory Medicine Program, said that while it's too early to pin the blame for the polio-like cases on EV-D68, health officials are right to further investigate a link.
"These clusters are very unusual," he said. "I think there is more and more evidence that this virus has been associated in several of these clusters with this."