CDC: Human Infection with highly pathogenic avian influenza A(H5N1) virus in Chile

April 18, 2023

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On March 29, 2023, Chile reported its first human infection with HPAI A(H5N1) virus. This is the second human case of A(H5N1) ever reported in South America, which includes a January 2023 case reported by Ecuador.

The Chilean patient was a 53-year-old man with symptom onset on March 13. He was hospitalized with severe illness and remains in respiratory isolation under multidisciplinary management, with mechanical ventilation due to pneumonia.

After hospital admission on March 22, the patient received antiviral treatment with oseltamivir and antibiotic treatment. HPAI A(H5) was detected in wild birds and sea lions in the Antofagasta region of coastal northern Chile where the patient lived. Potential contact of the patient with wild birds, marine mammals and/or environmental exposures remains under investigation. Close contacts of the patient have been asymptomatic and have tested negative for influenza viruses, indicating that no known human-to-human transmission occurred.

Viral RNA obtained from a bronchoalveolar lavage specimen from the patient has been sequenced and genetically analyzed by the National Influenza Centre in Chile (Instituto de Salud Pública) and by the Influenza Division/CDC. The virus was identified as having a clade 2.3.4.4b HA and was determined to be the same genotype that has been detected in the majority of wild birds in South America, indicating no evidence for genetic reassortment compared to A(H5N1) viruses predominating in birds in South America. The virus was 99% identical to many viruses identified in A(H5N1) virus-infected wild birds in Chile. Overall, the genomic analysis of the virus in this specimen does not change CDC’s risk assessment related to the avian A(H5) clade 2.3.4.4b viruses. The overall risk to human health associated with the ongoing A(H5) outbreaks in wild birds and poultry remains low.