Imagine this: A 15-year-old male presents to an urgent care center with a one-day history of fever, cough, and shortness of breath. He is mildly tachypneic with bilateral scattered crackles on lung exam. A rapid test for COVID-19 and influenza is positive for influenza A — a surprising result in June.
An oxygen saturation of 90% prompts transfer to the emergency department at the local children’s hospital. The emergency medicine fellow is skeptical of the presumptive diagnosis. Influenza in the summer in a boy who had not traveled outside his small hometown in the southeastern United States? A respiratory viral panel also detected influenza A, but the specimen did not type as influenza A H1 or H3. This result prompted the laboratory technician to place a call to the ordering physician. “Does this patient have risk factors for avian flu?” the tech asked.
University of Louisville
Dr. Kristina K. Bryant
Highly pathogenic avian influenza (HPAI) A(H5N1) is not a new virus. It was discovered in waterfowl in China in 1996 and has since evolved into multiple clades and subclades, spreading to every continent on the globe except Oceania. It is called highly pathogenic because it kills a large number of the birds that it infects. In 2021, Clade 2.3.4.4b HPAI A(H5N1) viruses emerged in North America, causing large outbreaks in wild birds and farmed poultry populations, including backyard flocks. Sporadic infections have been identified in a diverse group of mammals, including foxes, raccoons, baby goats, bears, and harbor seals. In March of this year, HPAI A(H5N1) was detected for the first time in United States dairy cattle. As we go to press, the United States Department of Agriculture has detected HPAI A(H5N1) in dairy cattle on 36 farms in 9 states.
Human infections are rare, but often severe. Following a 1997 outbreak of HPAI A(H5N1) in Hong Kong, 18 people were infected and 6 died. Since then, more than 900 cases have been reported in humans and approximately half of these have been fatal. The spectrum of disease includes asymptomatic infection and mild disease, as occurred recently in Texas. A dairy farm worker who was exposed to dairy cattle presumed to be infected with HPAI A(H5N1) developed conjunctivitis and no other symptoms. An individual infected in Colorado in 2022 had no symptoms other than fatigue and recovered.
Human-to-human transmission was not identified with either of these cases, although very limited, non-sustained transmission has been observed in the past, usually in family members of infected people after prolonged close exposure.
Right now, most people in the United States are not at risk for HPAI A(H5N1) infection.
Careful history taking with our illustrative and hypothetical case revealed exposure to farm animals but in a state without known cases of HPAI A(H5N1) in dairy cattle. State health department officials nevertheless agreed with further testing of the patient. Some influenza diagnostic tests cleared by the US Food and Drug Administration (FDA) can detect some novel influenza A viruses such as HPAI A(H5N1) but cannot distinguish between infection with seasonal influenza A or novel influenza A viruses. Molecular assays may give an “influenza A untypeable” result, as in our case. The CDC urges further testing on these untypeable specimens at local or state public health laboratories. When HPAI A(H5N1) is suspected, a negative result on a commercially available test is not considered sufficient to exclude the possibility of infection.
Our patient was admitted to the hospital and droplet, contact, and airborne precautions were instituted along with antiviral treatment with oseltamivir. Preliminary analysis of HPAI A(H5N1) viruses predicts susceptibility to currently available antivirals. The admitting physician confirmed that the boy had received influenza vaccine in the preceding season but, unfortunately, seasonal vaccines do not protect against HPAI A(H5N1) infection.