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TORONTO - The cold-causing bug, enterovirus D68, that's been making some children severely ill across the U.S. and now in parts of Canada has been around for decades, but doctors acknowledge there may be something different about the strain circulating this year.

The virus — also known as EV-D68 — tends to cause symptoms in the lower part of the respiratory system, putting children with asthma or wheezing at greater risk of developing more acute illness from the infection; most cold viruses typically affect the upper airways.

"At this time, we don't know why this virus has a predilection for the lower respiratory tract, why it's causing more severe respiratory illness," said Dr. Danuta Skowronski, an infectious diseases specialist the BC Centre for Disease Control.

"Those sort of secrets have yet to be found out," she said Monday from Vancouver, noting that studies need to be completed on EV-D68's genetic profile to tease out anything that might be unique to the strain.

There are more than 100 enteroviruses, the second most common cause of the common cold after rhinoviruses. But Skowronski said EV-D68 acts more like a rhinovirus than an enterovirus — it doesn't replicate in the acid-rich environment of the gastrointestinal tract and prefers temperatures around 33 C, unlike its namesake cousins.

EV-D68 typically starts with garden-variety cold symptoms — runny nose, sneezing and coughing — and most children infected with the virus have mild to moderate symptoms that resolve on their own.

But in some cases, the lower airways become compromised, leading to wheezing and difficulty breathing that requires prompt action, doctors advise parents.

"Certainly, if their children are developing signs of respiratory distress, with more laboured breathing, more rapid breathing, losing their appetite, then they really should be seeking medical attention, particularly going to the emergency department," said Dr. Upton Allen, chief of infectious diseases at Toronto's Hospital for Sick Children.

While there is no direct treatment against the virus, children may receive medications to ease airway constriction and be admitted to a ward for observation.

"The ones that come to hospital generally represent the more severe end of the spectrum," Allen said. "If they are among the most severely ill who require help with their breathing, then they would be admitted to an intensive care unit where they get ventilated."

As of Friday, the U.S. Centers for Disease Control said there were 160 confirmed cases of EV-D68 in 22 states, with many more possible or suspected cases being investigated.

Sick Kids recently admitted a dozen children to the ICU and all were on ventilators to help them breathe. But results of testing released Monday showed only one of the young patients was infected with enterovirus D68. The others had respiratory infections caused by other common cold viruses. The patient with EV-D68 has recovered and been discharged home, a spokeswoman said.

In B.C., Skowronski said there have been seven lab-confirmed cases of EV-D68, four in children aged under 10 and three aged between 10 and 19.

It's difficult to say how common it is for EV-D68 to send a child to the ICU and treatment with a ventilator. Most children who come down with a respiratory illness, even if they end up in the ER, aren't tested to see what virus is causing their infection, she said.

In previous EV-D68 outbreaks — there were at least six between 2008 and 2010 — about 20 per cent of the 100 cases described in the medical literature required ICU admission, Skowronski said. In Kansas City in mid-August, where the current outbreak was first identified, all of 19 confirmed cases were admitted to the ICU, while 90 per cent of the 11 cases in Chicago were given intensive care.

"Since we don't test everyone for enterovirus when they have symptoms, mild symptoms for instance, it may be that all of our surveillance is being skewed towards the more severe end of the spectrum," Skowronski said. "And children may be having more severe symptoms because of the combination of lack of immunity and smaller airways."

Immunity is a key issue: enterovirus D68 was first identified in 1962, and it may be that young children are more susceptible to the bug than adults because they have not been exposed to the virus before and therefore have no antibodies to fight it off.

That doesn't mean that adults can't contract EV-D68, said Allen, and those with existing lung diseases such as COPD could be at risk for more severe symptoms.

"It really is children with underlying conditions, and in particular those who have a history of asthma or wheezing, who are having the most difficult time with this virus," said Skowronski.

"So children who have that history, if they do develop a respiratory illness and it's worsening, with difficulty breathing, (parents) should seek medical care promptly or urgently, without delay in order to get the supportive care needed," she said, stressing that parents should trust their instincts.

Otherwise, kids should be kept home from school and get lots of rest and fluids until symptoms abate. "That is likely all that is needed for the vast majority," she said, adding that frequent hand-washing and other infection-control measures should be practised to prevent transmission of the virus to others.

Although EV-D68 caused three deaths in previous outbreaks, Allen said dying is not a "major feature" of the disease, and that if a patient were to sadly die, it "would not necessarily indicate a worsening of the outbreak, because that type of scenario can happen in any year."

To put the summer-fall spate of cases in context, Skowronski said enteroviruses generally pale in comparison with such respiratory microbes as, say, seasonal influenza, which kills thousands around the world each year, especially among the very young and very old.

"In part, we've created a scenario of outbreak by virtue of our diagnostic testing, both in terms of who we're testing and how we're testing that may have created this sense of alarm that's somewhat artificial," she said of widespread news reports on the outbreak.

"Having said that, since we have recognized this and since there are certain people who may be at higher risk, we ought to profit from that information and make sure that they get the care that they need.

"But the sky is not falling."

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News from © The Canadian Press, 2014