Health officials in British Columbia, Canada, have closed their investigation into how a teenager there became infected with the H5N1 bird flu for now because they have run out of leads to follow, the province’s public health officer said Tuesday.
Bonnie Henry said an extensive investigation into the people and pets the unnamed teen had contact with does not shed light on how the teen became infected. The virus was also not detected in environmental samples from locations in the area where he or she lives. The investigation also suggests there was no further transmission from the teen to anyone else, she said.
“I am confident that there are no new cases at this time, but we still need to be careful and we need to look and think about how we can prevent this from happening to anyone else,” Henry said at a news conference.
“Our detailed public health investigation is closed for now unless something new emerges.”
The teen is in serious condition in the hospital, on a ventilator and currently unable to breathe on his own. However, Henry noted that the teenager had shown some signs of progress in recent days, and there is hope for a recovery.
The teen initially sought medical attention on November 2 for conjunctivitis – infection of the lining around the eye. On November 8, the child was admitted to BC Children’s Hospital in Vancouver.
Genetic sequencing of the teenager’s virus, conducted at Canada’s National Microbiology Laboratory in Winnipeg, revealed it to be an H5N1 virus of clade 2.3.4.4b and genotype D1.1. This is not the same genotype of the virus spreading among dairy cows in the United States. It is a version of the virus isolated from wild birds that has caused 54 ongoing H5N1 outbreaks at poultry farms in British Columbia, mainly in the Fraser Valley, the area in southwest Vancouver where the teen lives.
However, Henry said a comparison of the teenager’s virus with other H5N1 virus sequences shows it is not closely related to the viruses isolated from affected poultry farms. Instead, the closest — though not perfect — match came to viruses recovered from two cackling geese found dead in the Fraser Valley in early October.
“So that tells us… that there may have been an intermediary, another bird or animal, between the detected geese and this young individual,” Henry said.
Analysis of the virus also showed signs that it was mutating in a way that made it easier to infect people. But the teenager is no longer viremic and therefore that mutated virus is extinct.
All people who had contact with the teenager while he or she was contagious – 34 healthcare workers and 16 close relatives and friends – tested negative for the virus. They all completed the 10-day incubation period during which flu symptoms would develop if an infection had occurred.
Twenty-five animals – birds, rodents, dogs, cats and reptiles – were tested for the virus; none were positive. Extensive testing was performed on a dog that was sick before the teen became ill, but again, none of those tests came back positive, Henry said. “We may never know exactly where they were exposed and where it came from,” she said, noting that earlier this year a person in Missouri tested positive for the virus and the source of the infection has never been determined.