Enterovirus D68, the virus linked to rare deaths and paralysis of children in Canada and the U.S. in 2014, is stronger than other respiratory infections but doesn't seem to increase the risk of death, a new study suggests.

Last fall, hospitals in the U.S. and then Canada reported hundreds of cases of severe respiratory illness caused by enterovirus D68 (EV-D68).

To find out more, researchers at McMaster Children's Hospital in Hamilton, Ont. compared the severity of illness of 87 children who tested positive for EV-D68 with controls the same age who did not have the virus.

"Enterovirus D68 seems  to be a more virulent pulmonary pathogen than rhinovirus [a common cold virus] or non-EV-D68 enterovirus, but we did not find a significant difference in death or need for critical care," Dr. Dominik Mertz of McMaster University and his co-authors said.

Patients with EV-D68 were more likely to have respiratory distress and more likely to be admitted to hospital and treated with certain medications, the researchers found.

They noted the U.S. Centers for Disease Control and Prevention documented 12 deaths under investigation in 1,152 confirmed cases for an estimated mortality of one per cent, which isn't far above the expected mortatlity associated with rhinovirus or other enterovirus infection.

In those study, those with EV-D68 admitted to hospital were also more likely to have a family history of allergies or asthma, known as atopic disease.

Dr. Michelle Science and Dr. Upton Allen of Toronto's Hospital for Sick Children wrote a journal commentary published with the study.

"It seems reasonable to hypothesize that EV-D68 may be a more virulent pulmonary pathogen in patients with pre-existing atopic disease when compared with rhinoviruses and other enteroviruses," the pair wrote.

They said the likely explanation for why infants, children and teens were predominantly affected in the outbreak is these age groups do not yet have immunity from past exposures.

More studies are needed to define whether EV-D68 is truly a more severe pathogen than other enteroviruses and rhinoviruses for all patients, or whether there are certain people are at increased risk of severe disease.

The study was not funded.