Influenza
Prognosis

People who are at least 65 years of age, due to a weakened immune system from aging or a chronic illness, are a high-risk group for developing complications, as are children less than one year of age and children who have not been previously exposed to influenza viruses multiple times. Pregnant women are at an elevated risk, which increases by trimester and lasts up to two weeks after childbirth. Obesity, in particular a body mass index greater than 35–40, is associated with greater amounts of viral replication, increased severity of secondary bacterial infection, and reduced vaccination efficacy. People who have underlying health conditions are also considered at-risk, including those who have congenital or chronic heart problems or lung (e.g. asthma), kidney, liver, blood, neurological, or metabolic (e.g. diabetes) disorders, as are people who are immunocompromised from chemotherapy, asplenia, prolonged steroid treatment, splenic dysfunction, or HIV infection. Tobacco use, including past use, places a person at risk. The role of genetics in influenza is not well researched, but it may be a factor in influenza mortality.
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