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Canadian public health officials closed their investigation into the teenager who became critically ill with the H5N1 bird flu virus, with no source of infection identified.

It’s not clear whether the teenager recovered or was released from the hospital. Andy Watson, director of communications for the Office of the Provincial Health Officer in British Columbia, said in an email to MedPage Today that the office does not provide patient status updates due to privacy.

The office “won’t be providing any updates on the status of the teenaged patient or this now complete investigation unless there is a need from a public health perspective to do so,” Watson said in the email.

During a press briefing 2 weeks ago, Provincial Health Officer for British Columbia Bonnie Henry, MD, MPH, said the teenager remained in critical care at BC Children’s Hospital in Vancouver. While the individual was stable, they were “still very sick.”

“Our thoughts remain with them and their family and we remain hopeful as they have made some progress in the last few days that they will recover from this very severe infection,” Henry said during the briefing.

Henry said the patient was young and healthy, with no underlying conditions. The infection started with conjunctivitis and progressed over several days to a severe lung infection.

Henry noted that among the 900 cases of H5N1 globally, young people tend to have more severe illness. “It may be that as we get older, we have some exposure to different influenza viruses, particularly with the N1 component, that might give us some protection from severe illness,” she said.

The investigation revealed no additional cases of H5N1 and no evidence of human-to-human transmission, and all testing on human, animal, and environmental samples were negative for H5N1. Public health officials assessed the 60 healthcare workers who had contact with the patient, along with 16 close family and friends, none of whom developed any illness.

A pet dog had been sick at the time of the patient’s onset of illness, but a thorough investigation of the dog turned up no evidence of H5N1 infection, Henry said.

Genetic testing showed the patient was infected with the same H5N1 strain seen in wild birds in British Columbia — clade 2.3.4.4b, genotype D1.1 — and that it most closely matched that of wild birds found in the Fraser Valley area in October. It was not related to outbreaks at poultry farms in British Columbia, Henry added.

However, investigators did see some changes in the genetic sequence that may signal adaptation to humans, and there were some mutations that were particularly concerning, including one that may have led the virus to more easily bind to receptors deep in the lung, causing more severe illness, she said.

Henry said the fact that a source of infection wasn’t found isn’t unusual, as there have been three cases in the U.S. — one in an adult in Missouri, and two in children in California — that don’t have an apparent source of infection.