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Influenza, commonly known as flu, is an infectious disease of birds and mammals caused by RNA viruses of the family Orthomyxoviridae (the influenza viruses). The name influenza comes from the Italian: influenza, meaning "influence", (Latin: influentia). In humans, common symptoms of the disease are fever, sore throat, muscle pains, severe headache, coughing, weakness and general discomfort. In more serious cases, influenza causes pneumonia, which can be fatal, particularly in young children and the elderly. Although it is sometimes confused with the common cold, influenza is a much more severe disease and is caused by a different type of virus. Influenza can produce nausea and vomiting, especially in children, but these symptoms are more characteristic of the unrelated gastroenteritis, which is sometimes called "stomach flu" or "24-hour flu."
Typically influenza is transmitted from infected mammals through the air by coughs or sneezes, creating aerosols containing the virus, and from infected birds through their droppings. Influenza can also be transmitted by saliva, nasal secretions, faeces and blood. Infections also occur through contact with these body fluids or with contaminated surfaces. Flu viruses can remain infectious for about one week at human body temperature, over 30 days at 0 ?C (32 ?F), and indefinitely at very low temperatures (such as lakes in northeast Siberia). Most influenza strains can be inactivated easily by disinfectants and detergents.
Symptoms of influenza can start quite suddenly one to two days after infection. Usually the first symptoms are chills or a chilly sensation but fever is also common early in the infection, with body temperatures as high as 39 ?C (approximately 103 ?F). Many people are so ill that they are confined to bed for several days, with aches and pains throughout their bodies, which are worst in their backs and legs.
Common symptoms of the flu such as fever, headaches, and fatigue come from the huge amounts of proinflammatory cytokines and chemokines (such as interferon or tumor necrosis factor) produced from influenza-infected cells. In contrast to the rhinovirus that causes the common cold, influenza does cause tissue damage, so symptoms are not entirely due to the inflammatory response. Symptoms of influenza may include:
· Body aches, especially joints and throat
· Coughing and sneezing
· Extreme coldness and fever
· Irritated watering eyes
· Nasal congestion
· Nausea and vomiting
· Reddened eyes, skin (especially face), mouth, throat and nose
It can be difficult to distinguish between the common cold and influenza in the early stages of these infections, but usually the symptoms of the flu are more severe than their common-cold equivalents.
Vaccination and infection control
Influenza vaccine is strongly recommended for high-risk groups, such as children and the elderly.
It is possible to get vaccinated and still get influenza. The vaccine is reformulated each season for a few specific flu strains, but cannot possibly include all the strains actively infecting people in the world for that season. It takes about six months for the manufacturers to formulate and produce the millions of doses required to deal with the seasonal epidemics; occasionally, a new or overlooked strain becomes prominent during that time and infects people although they have been vaccinated (as by the H3N2 Fujian flu in the 2003–2004 flu season). It is also possible to get infected just before vaccination and get sick with the very strain that the vaccine is supposed to prevent, as the vaccine takes about two weeks to become effective.
The 2006–2007 season is the first in which the CDC has recommended that children younger than 59 months receive the