|Synonyms||Flu, the flu|
|Influenza virus, magnified approximately 100,000 times|
|Usual onset||Two days after exposure|
|Frequency||3–5 million per year|
|Deaths||~375,000 per year|
Influenza, commonly known as "the flu", is an
Three of the four types of influenza viruses affect people, Type A, Type B, and Type C. Type D has not been known to infect people, but is believed to have the potential do so. Usually, the virus is
Frequent hand washing reduces the risk of viral spread. Wearing a
Influenza spreads around the world in a
Approximately 33% of people with influenza are asymptomatic.
Symptoms of influenza can start quite suddenly one to two days after infection. Usually the first symptoms are
It can be difficult to distinguish between the
The available laboratory tests for influenza continue to improve. The United States
Occasionally, influenza can cause severe illness including primary viral pneumonia or secondary bacterial pneumonia. The obvious symptom is trouble breathing. In addition, if a child (or presumably an adult) seems to be getting better and then relapses with a high fever, that is a danger sign since this relapse can be bacterial pneumonia.
Sometimes, influenza may have abnormal presentations, like confusion in the elderly and a sepsis-like syndrome in the young. Encephalitis due to the flu is rare but not unheard of. One patient and his sibling had a fever, severe diarrhea, and lowering consciousness, followed by seizures and a coma and eventually death without any respiratory disease. One elderly man had confusion, a steadily lowering Glasgow Coma Scale, and soon a coma. He survived, but he had residual neurological symptoms like paraplegia and urinary incontinence.