Key points
- Most human cases of bird flu, caused by avian influenza A(H5) virus, in the United States have been mild, so far, and most were in people who had known exposure to sick or infected animals.
- The severity of illness associated with bird flu has ranged from mild to severe, including death.
- The reported signs and symptoms of bird flu in humans have varied. Eye redness has been the predominant symptom among recent U.S. cases of avian influenza A(H5) virus infection. Respiratory symptoms and fever were also reported.
- The possibility of human infections with avian influenza virus that result in severe illness remains and underscores the importance of ongoing prevention and surveillance efforts.
Mild symptoms
Mild signs and symptoms of bird flu in people may include:
- eye redness and irritation (conjunctivitis)
- mild fever (temperature of 100ºF [37.8ºC] or greater) or feeling feverish*,
- cough
- sore throat
- runny or stuff nose
- muscle or body aches
- headaches
- fatigue
Eye redness has been the predominant symptom among recent U.S. cases of avian influenza A(H5) virus infection.
Less common symptoms include diarrhea, nausea, or vomiting.
*Fever may not always be present
Signs and Symptoms of Moderate to Severe Disease
Signs and symptoms of moderate to severe disease from bird flu in people may include:
- high fever or other symptoms listed above that limit or prevent usual activity
- shortness of breath or difficulty breathing
- altered consciousness
- seizures
Complications
Complications of bird flu can include but are not limited to:
- pneumonia,
- respiratory failure,
- acute respiratory distress syndrome,
- acute kidney injury
- multi-organ failure (respiratory and kidney failure),
- sepsis, septic shock
- and inflammation of the brain (meningoencephalitis)
Timing
Onset of Symptoms
The time from when a person is exposed and infected with avian influenza A(H5) viruses to when respiratory symptoms begin is about three days but can range from about 2 to 7 days. However, eye symptoms such as redness and irritation can occur one to two days after exposure and infection with an avian influenza A(H5) virus.
Period when people are contagious
- The period of contagiousness for person with mild illness due to bird flu is not well understood but thought to be similar to seasonal flu.
- People are thought to be most contagious during the first few days of their illness.
- People with severe disease (e.g., pneumonia) requiring hospitalization may have high levels of virus in the lower respiratory tract and may be contagious for several weeks.
How long bird flu illness lasts
Bird flu usually lasts a few days to less than two weeks, but how long symptoms last can vary by person. People who are severely ill (for example, intubated for severe pneumonia and respiratory failure) may be sick for several weeks.