The flu, or influenza, is a common and generally harmless viral infection that primarily affects the respiratory system. The flu, which is highly contagious, affects approximately 10% of the population of industrialized countries each winter. It is a significant cause of death in fragile individuals such as the elderly or immunodeficient. Although there is no curative treatment against the flu, vaccination offers good protection if it is renewed each year.
Sore throat, nasal congestion, and runny nose are most often the symptoms of a cold. High fever, stiffness and aching, headaches, and intense fatigue are generally associated with the flu.
Flu-like syndrome, or flu-like state, is a combination of symptoms caused by the flu: fever higher than 104°F (40°C), shivering, muscle and joint pain, headaches, and significant fatigue. It is also manifested in connection with other infectious diseases, most often of viral origin. In the case of the flu, flu-like syndrome appears within 48 hours after contamination by the virus and is accompanied by a generalized inflammation of the respiratory tract (nose, throat, trachea, bronchial tubes) and a dry cough. In general, the flu spontaneously resolves in one week. In people suffering from chronic cardiac or respiratory diseases, a secondary bacterial infection may cause pneumonia.
Drinking plenty of water or other liquids and getting bed rest usually makes it possible to relieve flu symptoms. Drugs such as antipyretics and analgesics may also be used to lower the fever and to relieve stiffness, aching, and headaches.
The flu is caused by the virus Myxovirus influenzae, which has a great ability to mutate. Thus, the flu virus is different each year and the vaccination must be renewed every year in order to be effective. The virus is spread by the microdroplets that come from sneezing and coughing and by direct contact with an infected person. Highly resistant, it is able to survive on objects such as a computer keyboard, a telephone, or a doorknob for at least 24 hours. Frequent washing of the hands in a period of epidemic thus remains one of the effective means of prevention.
Each year, seasonal flu epidemics cause between 250,000 and 500,000 deaths throughout the world. It is one of the most significant causes of death by an infectious disease. New strains of the flu virus, very different from the seasonal flu virus, appear periodically. They may result from the mutation of an existing virus or the combination of a human flu virus with a porcine or avian flu virus. These flus, against which humans are not immunized, are capable of infecting the population and spreading rapidly, causing a pandemic. For an unknown reason, this phenomenon occurs three or four times per century, as in the 20th century, during which there were pandemics of the Spanish flu (1918–1919), the Asian flu (1957– 1958) and the Hong Kong flu (1968–1969). It is difficult to predict the occurrence and the magnitude of a flu pandemic. Its symptoms may be identical to those of the seasonal flu or more severe, presenting a higher risk of death. The virus may also evolve and reappear with greater virulence. Scientists and governments are therefore vigilant when faced with the appearance of these new strains of the flu, as in the case of the avian flu virus of 2003 (H5N1) and the swine flu of 2009 (H1N1).
Faced with the risk of flu pandemic and in order to prepare to fight it, health authorities develop different strategies: implementation by the World Health Organization of a worldwide warning scale consisting of six phases, quarantining infected animals, development of a vaccine (the production of which can take several months). In case of an established flu pandemic and while awaiting a vaccine, it is preferable to limit traveling, particularly by public transportation, to avoid places with large concentrations of people, to wear a protective mask covering the nose and the mouth, and to systematically apply the elementary rules of hygiene such as washing and disinfecting the hands frequently, sneezing into a handkerchief or into one’s elbow, etc.