Description

• Human infection due to avian influenza type A viruses (subtypes H5N1 and H7N9 to date). H5N1 is highly pathogenic; H7N9 has low pathogenicity.
• Presents with influenza-like illness and (primarily) lower respiratory tract symptoms
• High mortality rate in elderly and very young (particularly H5N1)
• Synonym(s): bird flu, H5N1, H7N9

Epidemiology

Incidence

• >860 confirmed human cases A(H5N1) (53% fatality rate); most cases from Egypt and Indonesia
• 1,564 cases and 610 deaths A(H7N9) (mostly from China) since February 2013
• Predominant age: affects all age groups

Prevalence
Rare

Etiology and Pathophysiology

• Infected poultry (domesticated ducks, turkeys, chickens) reservoir
• Low incidence of human-to-human transmission, typically household clusters and health care workers
• Incubation period: 7 days (range 2 to 17 days)

Risk Factors

• Known direct contact with H5N1 or H7N9 virus or infected individual
• Contact with infected poultry
• Recent travel to endemic country (within 10 days of symptom onset)

General Prevention

• Consider isolating any patient with influenza-like symptoms who has had close contact with H5N1, H7N9, or ill poultry.
• Respiratory droplet precautions and N-95 masks
• There is an approved vaccine (H5N1) for adults 18 to 65 years of age.
• Consider antiviral chemoprophylaxis if H5N1 is circulating within the community; no postexposure chemoprophylaxis is recommended for H7N9 if travel exposure criteria are fulfilled.

Commonly Associated Conditions

Severe respiratory distress (common in severe cases)