Influenza, also known as flu, is an infectious disease caused by an influenza virus. Symptoms can be mildly severe. The most common symptoms include: high fever, nasal bleeding, sore throat, muscular pain, headache, cough, sneezing and tiredness. These symptoms usually start two days after exposure to the virus and last for less than a week. However, cough may last longer than two weeks. Children may have diarrhea and vomiting, but they are not common in adults. Diarrhea and vomiting are more common in gastroenteritis, which is an unrelated disease, and sometimes incorrectly known as "stomach flu" or "24-hour flu". Complications of influenza may include deterioration of previous health problems such as viral pneumonia, secondary bacterial pneumonia, sinus infection and asthma or heart failure.
Three out of four types of influenza virus affect humans: type A, type B, and type C. Type D is not known to infect humans, but it is believed that there is the ability to do this. Generally, the virus spreads in the air through cough or sneezes. It is believed that this happens at a relatively short distance. It can also spread by touching the surface contaminated by the virus and then touching the mouth or eyes. A person may be infectious for others before and during the symptoms. The infection can be confirmed by testing the throat, sputum, or nose for the virus. Many rapid tests are available; However, people can be infected even when the results are negative. A type of polymerase chain reaction that detects RNA of the virus is more accurate. Frequent washing reduces the risk of viral spread. Wearing a surgical mask is also useful. Annual vaccination against influenza is recommended by the World Health Organization for high-risk people. The vaccine is mostly effective against 3 or 4 types of flu. It is usually well tolerated.
Since the rapid development of the virus, the vaccine made for one year can not be useful in the next year. Antiviral drugs such as neurominides inhibitor oseltamivir, among others, have been used to treat influenza. The benefits of antiviral medicines that are otherwise healthy do not show more than their risk. People with other health problems have no benefits.