Last year’s enterovirus D68 outbreak more widespread than first thought: study

TORONTO – What a difference a year makes.

In late summer and fall of 2014, doctors were reporting clusters of children across the U.S. and Canada being hospitalized with severe respiratory distress due to enterovirus D68, a bug that hadn’t caused an outbreak in North America for years.

This year, it appears EV-D68 has disappeared from the mix of cold viruses giving people runny noses and congested lungs — but how long it will stay quiescent is anybody’s guess.

“I think we’re not going to see it this year,” said Dr. Danuta Skowronski, an infectious disease specialist at the B.C. Centre for Disease Control, who is involved in the tracking of pathogens like EV-D68.

“We found no enterovirus D68 detections between Aug. 1 and the end of September this year,” she said, referring to testing of patients with respiratory illnesses. Last year at this time, B.C. had already recorded 18 patients with EV-D68, 13 of whom needed to be hospitalized.

“I don’t say it’s been eliminated, but I don’t think it’s going to circulate at the kind of widespread epidemic levels” seen last year, Skowronski predicted.

And widespread it was — even more so than initially thought, suggests a study led by Skowronski and published online Thursday in the journal EuroSurveillance.

While most studies of the 2014 outbreak looked at only cases requiring hospital admission to determine incidence and prevalence rates, the B.C. study included both hospital- and community-based patients to get a more accurate picture of EV-D68’s effect on the population, using surveillance data from B.C., Alberta and Quebec.

Overall, researchers found an eight-fold increase in detections of the virus from October to December 2014, compared to the same period a year earlier.

They also found that an equal proportion of children and young adults who saw a community-based doctor for a respiratory illness tested positive for EV-D68, suggesting that a wide range of age groups was susceptible to the virus — not just children.

However, children infected with the virus were admitted to hospital at a rate 15 to 20 times higher than adults, Skowronski said. As well, kids under age 10 had a four- to five-fold higher rate of hospitalization related to EV-D68 than did those age 10 to 19.

“There were also interesting differences based on sex,” she said. “So boys had higher rates of hospitalization than girls, among children, but that wasn’t seen in adults.”

“And that might be tracked to one of the risk factors, which is asthma, and asthma rates are higher in pre-pubescent boys than in girls.”

During the outbreak, doctors found that patients with asthma who contracted EV-D68 had a higher risk of hospitalization, including care in the ICU and sometimes assisted ventilation.

“It may be that children are at higher risk for severe disease because they lack the kind of pre-existing immunity that adults have acquired from other enterovirus infections that may attenuate adult illness,” she said.

A frightening aspect of last year’s outbreak was that some patients developed neurological symptoms, including a condition called acute flaccid paralysis, which causes muscle weakening.

Of more than 200 EV-D68 cases confirmed in B.C. alone between Aug. 28 and Dec. 31, 2014, five patients developed neurological deficits which had not completely resolved nine to 11 months later, Skowronski said. Three other patients, all with underlying health complications, died after contracting the virus.

While national statistics from the 2014 outbreak aren’t available for Canada, the U.S. Centers for Disease Control reported more than 1,150 confirmed cases in 49 states and the District of Columbia from mid-August 2014 to Jan. 15, 2015, most of them among children.

“Additionally, there were likely millions of mild EV-D68 infections for which people did not seek medical treatment and/or get tested,” the CDC says on it website.

Skowronski said ongoing surveillance in both community and hospital settings is needed so researchers can learn more about EV-D68’s incidence, who’s most at risk of contracting the disease, and why some people develop neurological symptoms and others don’t.

“We shouldn’t let it go. We shouldn’t forget about it because we’re not experiencing it this year,” she said. “There may be several years between the last and the next cyclical peak and so we want to be ready to be able to address some of those why-type questions when we get another wave.”

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