Most human cases of bird flu in North America have been mild, a fact that’s underscored by a new study of the first 46 confirmed human H5N1 infections in the United States this year. But the case of an ill Canadian teen stands out because of its severity and because the source of exposure remains a mystery.
With the number of cases continuing to grow, leaders from the National Institutes of Health are calling for more action to tackle the bird flu outbreak.
The teenager, who was hospitalized with H5N1 infection in November, became critically ill and spent almost two weeks hooked up to machines that took over for her failing heart, lungs and kidneys, according to a report published Tuesday in the New England Journal of Medicine.
The 13-year-old had asthma and obesity but was otherwise in good health before catching H5N1. She recovered after aggressive treatment with a combination of three antiviral drugs, according to the report.
“She had multiorgan failure and was horribly ill,” said Dr. Megan Ranney, an emergency medicine physician and dean of the Yale School of Public Health, who was not involved with the girl’s care.
The teen was treated with extracorporeal membrane oxygenation, or ECMO, in which machines take over the work of the heart and lungs to give the body a chance to recover. She also had continuous dialysis to help remove toxins from her blood because her kidneys weren’t working, as well as plasma exchange, in which machines separate the clear part of the blood from blood cells so harmful substances can be removed.
“Were those extraordinary treatment modalities not available, she likely would not have lived,” Ranney said.
Health officials in British Columbia closed their investigation into the case late last month after being unable to find the virus in any of the household pets, nearby animals, or soil or water samples. Close monitoring of people who were around the teen determined that no one else caught the virus from her. At the time, it wasn’t clear whether she had recovered.
The new report on the teen’s case “clearly shows that a child who was otherwise generally healthy became sick and then got very, very ill in a matter of days. This is a very worrisome outcome that we should be much more concerned about happening with other infections,” said Dr. Jennifer Nuzzo, who directs the Pandemic Center at Brown University. She was not involved in the case.
The teen was infected with a newer variant of the H5N1 virus, D1.1, which is carried by wild birds. This variant has played a role in some infections of poultry workers in Washington, which were mild, and a recent human infection in Louisiana, which was severe.
In both severe infections – the teen’s and the case in Louisiana – the virus has shown changes that mean it might be adapting to humans, a finding that has put infectious disease experts on high alert since it increases the possibility of human-to-human spread.
“For this reason, we should be much more aggressive in conducting environmental surveillance for H5N1 to track the virus and to prevent people from becoming infected,” Nuzzo said.
The report of the first 46 human cases, also published Tuesday in the New England Journal of Medicine by researchers at the US Centers for Disease Control and Prevention, shows that most were exposed to infected animals or to raw milk.
Eye redness, or conjunctivitis, was the most common symptom in these farmworker infections, showing up in 42 of 46 cases (93%). Almost half of the workers had fevers, and more than a third reported respiratory symptoms. The average duration of illness was about four days.
The article also acknowledges that the official number of cases is an undercount. Although the CDC says there have been 66 confirmed cases in the US this year, recent testing on dairy farms found that 7% of workers had evidence of recent H5N1 infection in their blood.
In a commentary that accompanied the two studies, Dr. Jeanne Marrazzo, who directs the National Institute of Allergy and Infectious Diseases, says the mutations found in the virus isolated from the Canadian teen highlight an “urgent need for vigilant surveillance and assessment of the threat of human-to-human transmission.”
Surveillance has been hampered because of incomplete reporting of animal infections, she wrote. The US Department of Agriculture hasn’t been submitting critical details like the exact dates when animals have gotten sick or precise locations that help scientists track the evolution of a virus over time.
Taken together, she writes, the new reports of human cases show that the pace of human H5N1 infections has been accelerating. There have also been an increasing number of people with respiratory symptoms, like breathing problems or coughing, linked to their infections.
Although the overall number of human infections related to H5N1 has been low, the continued drip, drip, drip of human and animal detections is not a good sign.
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She and co-author Dr. Michael Ison, who is chief of the Respiratory Diseases Branch at NIAID, call for better cooperation between human and animal disease investigators, complete reporting of data from animal infections so scientists can better track how the virus is spreading, development of countermeasures like vaccines and antiviral medication, and more precautions to prevent infection, such as increased use of recommended personal protective equipment and education about the risks of being around sick animals.
“The risk is really going to come when this gets better at obviously infecting humans, and then we are faced with potential for human-to-human transmission,” Marrazzo said.