Influenza
| Influenza | |
|---|---|
| Synonyms | Flu, the flu |
 | |
| Influenza virus, magnified approximately 100,000 times | |
| Specialty | Infectious disease |
| Symptoms | Fever, runny nose, sore throat, muscle pains, headache, coughing, feeling tired[1] |
| Usual onset | Two days after exposure[1] |
| Duration | ~1 week[1] |
| Causes | Influenza viruses[2] |
| Prevention | Handwashing, surgical mask, influenza vaccine[1][3] |
| Medication | Antiviral drugs such as oseltamivir[1] |
| Frequency | 3–5 million per year[1] |
| Deaths | ~375,000 per year[1] |
Influenza, commonly known as "the flu", is an infectious disease caused by an influenza virus.[1] Symptoms can be mild to severe.[4] The most common symptoms include: a high fever, runny nose, sore throat, muscle pains, headache, coughing, and feeling tired.[1] These symptoms typically begin two days after exposure to the virus and most last less than a week.[1] The cough, however, may last for more than two weeks.[1] In children, there may be nauseaand vomiting, but these are not common in adults.[5] Nausea and vomiting occur more commonly in the unrelated infection gastroenteritis, which is sometimes inaccurately referred to as "stomach flu" or the "24-hour flu".[5] Complications of influenza may include viral pneumonia, secondary bacterial pneumonia, sinus infections, and worsening of previous health problems such as asthma or heart failure.[2][4]
Three types of influenza viruses affect people, called Type A, Type B, and Type C.[2] Usually, the virus is spread through the air from coughs or sneezes.[1]This is believed to occur mostly over relatively short distances.[6] It can also be spread by touching surfaces contaminated by the virus and then touching the mouth or eyes.[4][6] A person may be infectious to others both before and during the time they are showing symptoms.[4] The infection may be confirmed by testing the throat, sputum, or nose for the virus.[2] A number of rapid tests are available; however, people may still have the infection if the results are negative.[2] A type of polymerase chain reaction that detects the virus's RNA is more accurate.[2]
Frequent hand washing reduces the risk of viral spread.[3] Wearing a surgical mask is also useful.[3] Yearly vaccinations against influenza are recommended by the World Health Organization for those at high risk.[1] The vaccine is usually effective against three or four types of influenza.[1] It is usually well tolerated.[1] A vaccine made for one year may not be useful in the following year, since the virus evolves rapidly.[1] Antiviral drugs such as the neuraminidase inhibitor oseltamivir, among others, have been used to treat influenza.[1] Their benefits in those who are otherwise healthy do not appear to be greater than their risks.[7] No benefit has been found in those with other health problems.[7][8]
Influenza spreads around the world in a yearly outbreak, resulting in about three to five million cases of severe illness and about 250,000 to 500,000 deaths.[1] In the Northern and Southern parts of the world, outbreaks occur mainly in winter while in areas around the equator outbreaks may occur at any time of the year.[1] Death occurs mostly in the young, the old and those with other health problems.[1] Larger outbreaks known as pandemics are less frequent.[2] In the 20th century, three influenza pandemics occurred: Spanish influenza in 1918 (~50 million deaths), Asian influenza in 1957 (two million deaths), and Hong Kong influenza in 1968 (one million deaths).[9] The World Health Organization declared an outbreak of a new type of influenza A/H1N1 to be a pandemic in June 2009.[10] Influenza may also affect other animals, including pigs, horses, and birds.[
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