Influenza (the flu) is a contagious respiratory illness caused by influenza viruses. It can cause mild to severe illness, and at times can lead to death. It is not the common cold, nor is it the stomach flu.
Coughing or sneezing spreads influenza viruses from person to person. Sometimes people may become infected by touching something with flu viruses on it and then touching their mouth or nose. Most healthy adults may be able to infect others one day before symptoms develop and up to five days after becoming sick. That means that you may be able to infect someone else before you know you are sick, as well as while you are sick.
Some people, such as young children, pregnant women, older people and people with certain health conditions (see below), are at high risk for serious influenza complications. If you have a high risk condition and get flu symptoms, check with your doctor promptly.
Factors known to increase a person’s risk of getting serious complications from influenza:
Blood disorders (such as sickle cell disease)
Chronic lung disease (such as chronic obstructive pulmonary disease [COPD] and cystic fibrosis)
Endocrine disorders (such as diabetes mellitus)
Heart disease (such as congenital heart disease, congestive heart failure and coronary artery disease)
Metabolic disorders (such as inherited metabolic disorders and mitochondrial disorders)
Neurological and neurodevelopmental conditions
People younger than 19 years of age on long-term aspirin therapy
People with chronic obstructive pulmonary disease (COPD)
People with weakened immune systems due to disease or medication (such as people with HIV or AIDS, cancer or those on chronic steroids)
Other people at high risk:
Adults 65 years and older
Children younger than 2 years old
Pregnant women and women up to two weeks from end of pregnancy
American Indians and Alaska Natives