Provincial Health Officer Dr. Bonnie Henry steps away from the podium after speaking during a news conference in Vancouver, on Jan. 30, 2023.DARRYL DYCK/The Canadian Press
A British Columbia teenager was presumed to have pneumonia when they were admitted to hospital late last week, but after a series of tests the teen was found to have contracted a highly pathogenic version of avian influenza known as clade 2.3.4.4b. The teen remains in critical condition and is the first known human case of the potentially lethal virus in Canada.
Determining the source of the unusual infection has required investigative work by a small army of health and veterinary professionals. This group retraced the teen’s every step in the 10 days before the onset of their symptoms, interviewing any person they had come into contact with, visiting the places they had been and collecting samples from pets and other animals in the area.
The culprit remains unknown, so the work is continuing, including a more detailed postmortem on the family’s dog. The animal was euthanized around the same time the investigation began because of a “number of serious health issues,” said Provincial Health Officer Bonnie Henry during an interview Wednesday.
Earlier reports from Dr. Henry noted that all the people and pets the previously healthy teen had recently spent time with, including the family dog when it was sick, tested negative for avian flu.
“Every little piece of information helps us put the puzzle together over time,” Dr. Henry said.
She added, however, that the source may never be determined.
Provincial and federal officials have stressed that the risk of an average person becoming sick with bird flu remains low. But there are concerns about how the highly pathogenic strain of H5N1, which has decimated farmed and wild birds across North and South America, may evolve.
Data from the World Health Organization show 904 human cases of avian flu have been reported in 24 countries between January, 2003, and Sept. 27 of this year. About 51 per cent of those were fatal. People who work on poultry farms or who have sustained contact with sick wild animals are most at risk of falling ill with avian flu. Recent human cases in the U.S. related to animal outbreaks on cattle and poultry farms have been mild.
The B.C. teen has no connection to poultry farms, making their case especially rare.
The province has declined to provide the age and gender of the patient.
On Nov. 8, Dr. Henry, after learning of the teen’s diagnosis, jumped on a call with about 15 people, including hospital clinicians, laboratory technicians, provincial officials and occupational health and safety staff, to kick-start their investigation. There are now 50 people working at any given time to uncover the source, she said.
Close family members and friends who had contact with the teen during the infectious period were contacted over the following days, in addition to two-thirds of the health care staff who had cared for the patient. Site visits to the teen’s home in a suburban neighbourhood in the Fraser Valley, the family’s veterinarian’s office and friends’ houses were also completed, with samples taken for examination.
On Wednesday, Nov. 13, Canada’s top laboratory confirmed that the teen was indeed infected with clade 2.3.4.4b. Dr. Henry said the working group can now compare the genomic information of the patient with tests done on infected wild birds in B.C. to see how closely they are connected.
“This can help us narrow our focus again on potential places where they might have been exposed,” she said.
Theresa Tam, Canada’s Chief Public Health Officer, said in an interview Wednesday that human cases in which the source of the infection cannot be identified are “rare and sporadic,” pointing to individual cases in Missouri and Mexico earlier this year. In both instances, the infected person had no history of exposure to poultry, dairy cows or other animals.
Dr. Tam added that investigators have been unable to speak with the B.C. teen because of their medical condition, which adds to the difficulty of pinpointing a source. She said the increasing number of animals, and particularly mammals, contracting avian flu is intensifying the risk of irregular human infection, but there is no evidence of sustained human-to-human transmission.
She noted, however, that the virus continues to evolve and could pose greater risks in the future.
The Canadian Food Inspection Agency currently tests milk for the presence of H5N1 but has not found any traces of avian influenza virus in retail or unprocessed milk samples. The federal government is not yet monitoring for the H5N1 subtype in wastewater, Dr. Tam said, but is watching jurisdictions such as the United States to determine the usefulness of such monitoring.
Matthew Miller, Canada research chair in viral pandemics and director of the Michael G. DeGroote Institute for Infectious Disease Research at McMaster University, said Canada must do more to prevent human cases of avian flu.
He said biosecurity measures need to be enhanced in high-risk environments, adding that safety measures must be bolstered among hunters, pet owners and others who may come across infected animals. He said Canada’s almost exclusive focus on responding to cases of avian flu rather than preventing them is misguided.
“Getting hit by lightning is really rare, and yet, every time there is a thunderstorm, we clear golf courses and we stop recreational youth games,” he said. “I find it frustrating that there seems to be this sense of complacency for infectious diseases, where you know the possible consequences are enormous because the risk is not an individual risk, the same way it is for a lightning strike – it’s a population-level risk.”
With a file from Kelly Grant in Toronto