Cause of B.C. teen's H5N1 avian flu infection still unknown, health officials say

B.C. health officials say they still don't know how a teenager became infected with the H5N1 strain of avian flu but say no further cases have been identified.

Earlier this month, health officials announced they were investigating what was believed to be the first human case of H5N1 avian influenza caught in Canada.

The teenager is still in critical condition, the province said Tuesday. 

The Ministry of Health says the teen is from the Fraser Health region, which includes several of Vancouver's eastern and southern suburbs and the Fraser Valley. 

According to the ministry, avian influenza — also known as bird flu — is a virus that primarily affects birds but can occasionally spread to humans through contact with infected animals or contaminated environments.

While human infections with avian influenza are rare, Health Canada says symptoms can range from mild to severe, potentially leading to pneumonia, organ failure and even death.

Provincial Health Officer Dr. Bonnie Henry said her thoughts are with the teen and their family.

"I am confident in the extensive public health investigation that was led by the Fraser Health team in partnership with the [B.C. Centre for Disease Control's] Public Health Laboratory, our partners at B.C. Children's Hospital and the chief veterinary officer," she said in a statement Tuesday.

In the time since B.C. announced the case, the U.S. Centers for Disease Control confirmed the first case of a child with H51N1 bird flu, in California. In that case, the centre said, the child experienced mild symptoms and is successfully recovering from the illness. An investigation into the source of that exposure is ongoing.

 In total, 55 confirmed cases of H5 bird flu have been reported in the United States in 2024, where the disease has been detected in cattle, poultry flocks, wild birds and mammals and more, including isolated reports of infections in goats and one pig.

The B.C. Centre for Disease Control says it has been working with the Canadian Food Inspection Agency and other Canadian and U.S.-based agencies to monitor the spread of the disease.

The investigation of the case of the teenager in B.C. with H5 avian flu included testing of pets, birds and other animals from nearby premises as well as environmental testing of soil and water, according to the province.

The investigation determined that the strain the teen contracted closely matches the strain found in wild birds in the Fraser Valley area in October and was not directly related to outbreaks at poultry farms in B.C.

It also found no additional cases or evidence of human-to-human transmission.

Since early October, the H5N1 virus has been detected in animals at numerous sites in B.C., including 22 poultry farms and in a variety of wild birds and small mammals such as foxes and skunks.

Millions of birds infected

In 2004, two poultry farm workers in the Fraser Valley fell ill with the H7N3 strain of avian flu. According to Public Health Canada, H7N3 typically presents with mild symptoms, while H5N1 typically presents as severe.

Since 1997, over 900 human cases have been reported globally, primarily in Asia and Africa, with about half of them resulting in death, according to Health Canada. However, the government cautions this fatality rate may be overestimated, as mild infections can often go undetected and underreported.

The Canadian Food Inspection Agency says that as of Nov. 20, 54 sites were actively dealing with avian flu infections in B.C — the highest number among provinces.

Over 6.8 million birds in B.C. are estimated to have been affected.

In light of the confirmed cases among animals in B.C., officials are recommending that residents avoid direct contact with sick or dead animals, keep pets away from affected wildlife and report any dead or ill birds or mammals to provincial authorities.