Influenza, commonly known as "the
flu", is an
infectious disease caused by an
influenza virus. Symptoms can be mild to severe. The most common
symptoms include: a high
fever,
runny nose,
sore throat,
muscle pains,
headache,
coughing, and
feeling tired. These symptoms typically begin two days after exposure to the virus and most last less than a week. The cough, however, may last for more than two weeks. In children, there may be
nausea and
vomiting, but these are not common in adults. Nausea and vomiting occur more commonly in the unrelated infection
gastroenteritis, which is sometimes inaccurately referred to as "stomach flu" or "24-hour flu". Complications of influenza may include
viral pneumonia, secondary
bacterial pneumonia,
sinus infections, and worsening of previous health problems such as
asthma or
heart failure.
