Highly Pathogenic Avian Influenza A(H5N1)

Highly pathogenic avian influenza A(H5N1) viruses have led to significant infections in poultry and dairy cows in the United States, with occasional human cases reported. This study outlines the characteristics of human A(H5N1) cases identified from March to October 2024 in the developed country.

The researchers examined data from individuals with laboratory-confirmed A(H5N1) infections, using a standardized case-report form linked to lab results from the CDC's influenza A/H5 subtyping kit.

The results demonstrated:

• Among 46 affected individuals, 20 had contact with infected poultry, 25 with infected or potentially infected dairy cows, and 1 had no known exposure; this individual was hospitalized with non-respiratory symptoms and was diagnosed via routine surveillance. 
• Of the 45 with animal exposure, the median age was 34 years; all experienced mild A(H5N1) illness, with none requiring hospitalization or resulting in death.
• Symptoms included conjunctivitis in 93% of patients, fever in 49%, and respiratory symptoms in 36%; 33% had only conjunctivitis. 
• The median illness duration for 16 patients was 4 days (ranging from 1 to 8 days). 
• Most patients (87%) were treated with oseltamivir, starting a median of 2 days after symptoms began. 
• No new cases emerged among the 97 household contacts of those with animal exposure
• Commonly used personal protective equipment (PPE) among exposed workers included gloves (71%), eye protection (60%), and face masks (47%). 

To conclude, the identified A(H5N1) cases were generally mild, primarily causing conjunctivitis and occurring in adults exposed to infected animals. Most patients received timely antiviral treatment, and there was no evidence of human-to-human transmission. However, the use of PPE among those in contact with infected animals was inadequate, indicating a need for improved strategies to minimize exposure risk.

Source: Garg S, et al. Highly Pathogenic Avian Influenza A(H5N1) Virus Infections in Humans. 

The New England Journal of Medicine. December 31, 2024. DOI: 10.1056/NEJMoa2414610