History and exam

Key diagnostic factors

Can be dry or productive. Blood-tinged sputum has been described but is not common.

Some nonspecific symptoms consistent with influenza-like illness have been reported (including conjunctivitis, rhinorrhea, headache, sore throat, myalgia, and fatigue).

Ranges from mild to severe.

Usually temperature >100.4°F (38°C) occurs early in course of illness and often persists, especially with severe illness.

Auscultatory finding described in highly pathogenic avian influenza (HPAI) H5N1 patients.

Auscultatory finding described in highly pathogenic avian influenza (HPAI) H5N1 patients.

Auscultatory finding described in highly pathogenic avian influenza (HPAI) H5N1 patients.

Usually develops within 5 days of illness onset.

Other diagnostic factors

Several nonspecific primary gastrointestinal symptoms have been reported in children and adults with highly pathogenic avian influenza (HPAI) H5N1 virus infection.

Nonspecific neurologic symptoms have been reported.

Nonspecific neurologic symptoms have been reported.

Risk factors

Direct contact (touching) or close (within ≤1 m) exposure with sick or dead poultry or other birds suspected or confirmed to have highly pathogenic avian influenza (HPAI) H5N1 virus infection.

Most people with HPAI H5N1 virus infection had direct or close unprotected exposure with infected sick or dead poultry before illness onset, but exposure appears to rarely result in HPAI H5N1 virus infection. Every year, many people are exposed to HPAI H5N1 virus but only a very small proportion become infected.

A recent history of travel to an HPAI-H5N1 virus-affected country should also prompt consideration of HPAI H5N1 virus infection in the differential diagnosis of a patient presenting with fever and respiratory symptoms. A traveler who had returned to Canada after visiting China presented with fever, pleuritic chest pain, and abdominal pain, and progressed to lower respiratory tract disease with meningoencephalitis and died of HPAI H5N1 virus infection.[21]

Direct contact (touching) with poultry feces and visiting a live poultry market in highly pathogenic avian influenza (HPAI) H5N1-endemic countries are risk factors for infection.[40][41]

Exposure to pond water in regions where HPAI H5N1 has been widespread among birds has also been suggested as a possible risk factor.[65] Most people with HPAI H5N1 virus infection had unprotected direct or close contact with infected sick or dead poultry before illness onset, but exposure appears to rarely result in HPAI H5N1 virus infection. Every year, many people are exposed to HPAI H5N1 virus but only a small proportion become infected.

The risk is highest among blood-related family members.[45] Rarely implicated risk factor, usually in caregivers of an ill blood-related family member. Risk is defined as prolonged direct or close unprotected contact (within 1-2 m) with ill people suspected or confirmed to have highly pathogenic avian influenza (HPAI) H5N1 virus infection. Nosocomial transmission of HPAI H5N1 virus from a patient to a healthcare worker has been reported.[48] However, serologic surveys of healthcare personnel using no or inadequate personal protective equipment while caring for patients with confirmed HPAI H5N1 virus infection have demonstrated very low risk of transmission.[66][67][68]

Highly pathogenic avian influenza (HPAI) H5N1 virus transmission to laboratory workers using proper techniques and personal protective equipment in appropriate biosafety precautions has not been documented.

Biosafety level 2 practices and procedures are the minimum requirement for handling specimens suspected to contain HPAI H5N1 virus.[69] Biosafety level 3-enhanced containment standards are the minimum requirement for culture of suspected HPAI H5N1 virus.[69] A small serosurvey of laboratory workers exposed to HPAI H5N1 virus with incomplete personal protective equipment use and adherence to biosafety precautions demonstrated no serologic evidence of prior HPAI H5N1 virus infection.[70]

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