Investigation into teen’s bird flu case concludes in B.C. with source still unknown

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British Columbia has closed its investigation into the first known human case of avian influenza contracted in Canada despite having been unable to determine the source of the infection, Provincial Health Officer Bonnie Henry says.

A teenager, whose age and gender are not being released by the province, remains in critical condition after contracting a highly pathogenic version of H5N1 known as clade 2.3.4.4b. in early November. Dr. Henry said Tuesday that the young person is unable to breathe on their own but that “we remain hopeful as they have made some progress in the last few days.”

The extensive public-health investigation involved contact tracing with dozens of health care workers, family and friends who had been in contact with the teen, in addition to the testing of more than 25 animals and 10 environmental samples, including sediment and wastewater, Dr. Henry said during a news conference. All tested negative for avian flu.

However, she said genetic sequencing found that the case is likely connected to wild birds, not farmed poultry. The closest match was related to two geese from Fraser Valley that were tested in early October, but it was not a direct link. Dr. Henry said this signals that there may have been another bird or animal that spread the virus between the infected geese and the teen.

“In the absence of being able to talk directly to this teen, we may not ever know for certain where they were exposed and where it came from,” she said, adding that there are many unknowns regarding whether the adolescent will recover and to what extent. “There are no further leads right now and there’s no further indication of transmission, so our investigation has come to a close.”

Dr. Henry said the investigation could be reopened should new details become known.

Here’s what you need to know about avian flu

Provincial and federal officials have stressed that human-to-human transmission of avian influenza is rare and that the risk to the general public is low although widespread infections have been detected in domestic and wild birds, in addition to some mammals.

However, public-health officials are concerned that the risk to humans is increasing as the virus mutates. Dr. Henry said the B.C. case is a “warning sign.”

She said there is an awareness of the “pandemic potential” of H5N1, particularly as more humans and other animals, particularly mammals, are exposed to the virus. The detection of the virus in pigs is “particularly worrisome” because they can carry both the animal and human strain, added Dr. Henry. She said the province is focused on surveillance to detect cases early on.

The previously healthy B.C. teen was diagnosed with avian flu on Nov. 8, which prompted a small army of health and veterinary officials to investigate the exposure. The teen first presented with pink eye but quickly developed a severe lung infection.

One potential culprit was the family dog that was sick and euthanized around the same time as the teen became ill. Dr. Henry said there have only been two known cases of canine H5 in the world. One such case occurred last year in Oshawa, Ont., where a domestic dog died after chewing on a wild goose.

The pet dog was “thoroughly investigated with every test possible” and colleagues were consulted across Canada and in the United States, said Dr. Henry, but it was determined the pet was negative for avian flu. Investigators then tested humans and other animals from the dog’s veterinary clinic and former home. Again, all tests came back negative.

Genetic sequencing helped B.C. officials narrow down the source but still fell short. This was always a possibility, said Dr. Henry, but shouldn’t be cause for concern.

“I am very confident that there are no additional cases out there right now,” she said. “It reminds us that there is always that risk, and we need to be vigilant for that and we need to take those measures that protect us individually and as a community.”