(CNN) — The first person to have a severe case of H5N1 bird flu in the United States has died, according to the Louisiana Department of Health. This is the first human death from bird flu in the US.
The person, who was over 65 and reportedly had underlying medical conditions, was hospitalized with the flu after exposure to a backyard flock of birds and to wild birds.
Louisiana health officials said that their investigation found no other human cases linked to this patient’s infection.
Flu experts have been warning that the H5N1 virus would bare its teeth as infections spread.
“We’ve been studying the family tree of this virus for 25 odd years, and this is probably the nastiest form of the virus that we’ve seen. So the fact that it finally did cause a fatal infection here is tragic but not surprising,” said Dr. Richard Webby, who directs the World Health Organization Collaborating Center for Studies on the Ecology of Influenza in Animals and Birds at St. Jude’s Children’s Research Hospital.
Since 2003, there have been roughly 900 human bird flu infections reported globally, and about half of those people have died, according to the World Health Organization. That would give the virus a 50% case fatality rate, making it extraordinarily lethal – but experts don’t actually think it kills half the people it infects.
Because severe cases are more likely to be reported than mild ones, mild illnesses probably aren’t being factored into that figure.
But even if the actual case fatality rate were 10 times lower – about 5% – it would still be a serious virus to contend with. The case fatality rate for the ancestral strain of Covid-19 was estimated to be around 2.6%, for example.
A recent study by scientists from the US Centers for Disease Control and Prevention on the first 46 human cases of H5N1 in the US last year found that they were nearly all mild and, except one, happened after exposure to infected farm animals.
The Louisiana patient was infected with the D1.1 clade of the bird flu virus, a strain that is circulating in wild birds and poultry. It’s different from the variant that’s circulating in dairy cattle.
Scientists don’t know whether it is associated with more severe disease in people. D1.1 also infected a critically ill teenager who was hospitalized in Canada. The teen, a 13-year-old girl, received intensive care and recovered, but investigators don’t know how she was exposed.
D1.1 infections have also been identified in poultry farm workers in Washington. Those cases appear to have been milder.
The CDC reported in late December that a genetic analysis of the virus that infected the Louisiana patient found changes expected to enhance its ability to infect the upper airways of humans and help it to spread more easily from person to person. Those same changes were not seen in the birds the person had been exposed to, officials said, indicating that they had developed in the person after they were infected.
CDC officials are continuing to investigate the case by looking at the virus in “serial samples” or blood tests taken from the patient over time. That will give them more information about how the virus was evolving in the patient’s body.
“The evolution of the virus is concerning but highlights how we need to prevent each possible spillover infection to reduce the risk of onward transmission to others,” said Dr. Seema Lakdawala, a microbiologist and immunologist who studies influenza transmission at the Emory University School of Medicine.
Although the overall risk to the public remains low, people who keep chickens and other birds in their backyards are at higher risk for bird flu, as are workers on dairy and poultry farms.
People who work with animals, or who have been in contact with sick or dead animals or their droppings, should watch for breathing problems and red eyes for 10 days after exposure. If they develop symptoms, they should tell their health care provider about their recent exposure.
Other ways to stay safe include:
- Do not touch sick or dead animals or their droppings, and do not bring sick wild animals into your home.
- Keep your pets away from sick or dead animals and their feces.
- Do not eat uncooked or undercooked food. Cook poultry, eggs and other animal products to the proper temperature, and prevent cross-contamination between raw and cooked food.
- Avoid uncooked food products such as unpasteurized raw milk or cheeses from animals that have a suspected or confirmed infection.
- If you work on a poultry or dairy farm, talk to a health care provider about getting your seasonal flu vaccination. It will not prevent infection with avian influenza viruses, but it can reduce the risk of coinfection with avian and more common flu viruses.
- Report dead or sick birds or animals to the US Department of Agriculture toll-free at 1-866-536-7593.
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