The fate of a Canadian teenager who was infected with H5N1 bird flu in early November, and subsequently admitted to an intensive care unit, has finally been revealed: She has fully recovered.
But genetic analysis of the virus that infected her body showed ominous mutations that researchers suggest potentially allowed it to target human cells more easily and cause severe disease — a development the study authors called “worrisome.”
The case was published Tuesday in a special edition of the New England Journal of Medicine that explored H5N1 cases from 2024 in North America. In one study, doctors and researchers who worked with the Canadian teenager published their findings. In the other, public health officials from across the U.S. — from the Centers for Disease Control and Prevention, as well as state and local health departments — chronicled the 46 human cases that occurred between March and October.
There have been a total of 66 reported human cases of H5N1 bird flu in the U.S. in 2024.
In the case of the 13-year-old Canadian child, the girl was admitted to a local emergency room on Nov. 4 having suffered from two days of conjunctivitis (pink eye) in both eyes and one day of fever. The child, who had a history of asthma, an elevated body-mass index and Class 2 obesity, was discharged that day with no treatment.
Over the next three days, she developed a cough and diarrhea and began vomiting. She was taken back to the ER on Nov. 7 in respiratory distress and with a condition called hemodynamic instability, in which her body was unable to maintain consistent blood flow and pressure. She was admitted to the hospital.
On Nov. 8, she was transferred to a pediatric intensive care unit at another hospital with respiratory failure, pneumonia in her left lower lung, acute kidney injury, thrombocytopenia (low platelet numbers) and leukopenia (low white blood cell count).
She tested negative for the predominant human seasonal influenza viruses — but had a high viral loads of influenza A, which includes the major human seasonal flu viruses, as well as H5N1 bird flu. This finding prompted her caregivers to test for bird flu; she tested positive.
As the disease progressed over the next few days, she was intubated and put on extracorporeal membrane oxygenation (ECMO) — a life support technique that temporarily takes over the function of the heart and lungs for patients with severe heart or lung conditions.
She was also treated with three antiviral medications, including oseltamivir (brand name Tamiflu), amantadine (Gocovri) and baloxavir (Xofluza).
Because of concerns about the potential for a cytokine storm — a potentially lethal condition in which the body releases too many inflammatory molecules — she was put on a daily regimen of plasma exchange therapy, in which the patient’s plasma is removed in exchange for donated, health plasma.
As the days went by, her viral load began to decrease; on Nov. 16, eight days after she’d been admitted, she tested negative for the virus.
The authors of the report noted, however, that the viral load remained consistently higher in her lower lungs than in her upper respiratory tract — suggesting that the disease may manifest in places not currently tested for it (like the lower lungs) even as it disappears from those that are tested (like the mouth and nose).
She fully recovered and was discharged sometime after Nov. 28, when her intubation tube was removed.
Genetic sequencing of the virus circulating in the teenager showed it was similar to the one circulating in wild birds, the D1.1 version. It’s a type of H5N1 bird flu that is related, but distinct, from the type circulating in dairy cows and is responsible for the vast majority of human cases reported in the U.S. — most of which were acquired via dairy cows or commercial poultry. This is also the same version of the virus found in a Louisiana patient who experienced severe disease, and it showed a few mutations that researchers say increases the virus’ ability to replicate in human cells.
In the Louisiana case, researchers from the CDC suggested the mutations arose as it replicated in the patient and were were not likely present in the wild.
Irrespective of where and when they occurred, said Jennifer Nuzzo, director of the Pandemic Center at Brown University in Providence, R.I., “it is worrisome because it indicates that the virus can change in a person and possibly cause a greater severity of symptoms than initial infection.”
In addition, said Nuzzo — who was not involved in the research — while there’s evidence these mutations occurred after the patients were infected, and therefore not circulating in the environment “it increases worries that some people may experience more severe infection than other people. Bottom line is that this is not a good virus to get.”
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