While most human disease in the current influenza A(H5N1) outbreak has been mild, severe cases have been reported; thus, vigilance is required.
Highly pathogenic avian influenza A(H5N1) viruses have spread across continents since 2021, most recently causing an outbreak in U.S. dairy cattle. Now, CDC investigators describe the clinical characteristics of influenza A (H5N1) infections between March and October 2024 identified in occupationally exposed persons or via routine influenza surveillance. Among 46 patients (median age, 34 years, 80% male, 89% Hispanic or Latino) in six states, the exposure source was dairy cows or poultry in all except one. Conjunctivitis was the most commonly reported symptom (93%), followed by feverishness (49%), sore throat (29%), and cough (18%). Oseltamivir was administered to 87% of patients. No viral transmission occurred to 97 household contacts, and no patient was hospitalized. Viral PCR was positive in 88% of conjunctival swabs and 33% of nasopharyngeal swabs.
In November 2024, a 13-year-old girl was discharged home from an emergency department in Canada after presenting with conjunctival symptoms and fever. Her condition subsequently developed to include respiratory and gastrointestinal symptoms; she was admitted to the hospital 3 days later with hemodynamic instability that progressed to multisystem organ failure requiring ECMO support. She received oseltamivir, baloxavir, and amantadine. Genetic sequencing revealed the virus to be closely related to that circulating in local wild birds. The patient was extubated 24 days after onset of symptoms.