Enterovirus D68: Explaining Hamilton's 139 cases

Health officials across the country have been releasing numbers of children diagnosed with Enterovirus D-68 (EV-D68), the polio-like disease that begins as a respiratory condition, but has caused some muscle weakness, paralysis and even deaths. A 4-year-old boy in New Jersey died after contracting the virus, despite showing no symptoms.

In Manitoba, three tested positive. Saskatchewan has reported 13 cases so far. In B.C., nine cases have been in reported, while in Alberta, 50 cases have been confirmed. 

So, why have there been 139 cases in Hamilton?

And they're still testing for more. Which is exactly the reason doctors here say the number is too high. 

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"We do a lot more testing for routine admission to hospital," said Dr. Marek Smieja, head of virology at Hamilton Regional Laboratory Medicine, the lab that has handled testing out of McMaster Children's Hospital. "We simply test an awful lot more."

Early testing, delayed symptoms and a short window

There have been no deaths in Canada, although it's been reported that the Centre for Disease Control and Prevention (CDC) has confirmed four deaths since the respiratory virus broke out in mid-August. 

The CDC reported 538 cases of EV-D68 across 43 states in the U.S. 

Smieja explained three factors as to why Hamilton has so many cases: early testing, delayed onset of symptoms, and a short window to test for. 

Hamilton tests roughly 6,000 to 7,000 kids a year for enterovirus, Smieja said. Other hospitals are "not usually looking," he added, saying many hospitals do not have the capability of Hamilton, and can only test for more common things like influenza. 

Smieja also said that by testing at admission, they're catching the cases that others may miss. Symptoms typically start out like the common cold. In extreme cases, muscle weakness and even paralysis have been reported. Hamilton only has four of such cases, and only half of the children with a respiratory problem showing muscle weakness have tested positive for EV-D68 -- it's not that doctors have ruled it out, it's a problem that EV-D68 may only be detectable for between three and seven days. 

Meaning if they child recovered, EV-D68 could have been missed. 

Smieja: 'We likely have peaked'

Smieja called the statistical anomaly a cases of testing "much more and much sooner," even adding that as the fall sets in, the enterovirus season dwindles. 

"We likely have peaked," Smieja said of the EV-D68 breakout. 

While it may bring comfort to some, the disease is still very much an unknown. EV-D68 works on a "similar mechanism" to polio, a respiratory condition which leads to damage of the spinal cord which causes paralysis. Whether that damage is permanent, has yet to be determined. 

"We don't know," Smieja said, speaking about the paralysis. "This particular neurological system is incredible rare … It's something we're all very puzzled by."