Global InformationInfluenza information
| Influenza | |
|---|---|
| Other names | flu, the flu, grippe (French for flu) |
 | |
| Influenza virus, magnified approximately 100,000 times | |
| Specialty | Infectious disease |
| Symptoms | Fever, runny nose, sore throat, muscle pain, headache, coughing, fatigue |
| Usual onset | 1–4 days after exposure |
| Duration | 2–8 days |
| Causes | Influenza viruses |
| Prevention | Hand washing, flu vaccines |
| Medication | Antiviral drugs such as oseltamivir |
| Frequency | 3–5 million severe cases per year[1][2] |
| Deaths | >290,000–650,000 deaths per year[3][4] |
Influenza, commonly known as "the flu" or just "flu", is an infectious disease caused by influenza viruses. Symptoms range from mild to severe and often include fever, runny nose, sore throat, muscle pain, headache, coughing, and fatigue. These symptoms begin one to four (typically two) days after exposure to the virus and last for about two to eight days. Diarrhea and vomiting can occur, particularly in children. Influenza may progress to pneumonia from the virus or a subsequent bacterial infection. Other complications include acute respiratory distress syndrome, meningitis, encephalitis, and worsening of pre-existing health problems such as asthma and cardiovascular disease.
There are four types of influenza virus: A, B, C, and D. Aquatic birds are the primary source of Influenza A virus (IAV), which is also widespread in various mammals, including humans and pigs. Influenza B virus (IBV) and influenza C virus (ICV) primarily infect humans, and influenza D virus (IDV) is found in cattle and pigs. IAV and IBV circulate in humans and cause seasonal epidemics, and ICV causes a mild infection, primarily in children. IDV can infect humans but is not known to cause illness. In humans, influenza viruses are primarily transmitted through respiratory droplets from coughing and sneezing. Transmission through aerosols and surfaces contaminated by the virus also occur.
Frequent hand washing and covering one's mouth and nose when coughing and sneezing reduce transmission. Annual vaccination can help to provide protection against influenza. Influenza viruses, particularly IAV, evolve quickly, so flu vaccines are updated regularly to match which influenza strains are in circulation. Vaccines provide protection against IAV subtypes H1N1 and H3N2 and one or two IBV subtypes. Influenza infection is diagnosed with laboratory methods such as antibody or antigen tests and a polymerase chain reaction (PCR) to identify viral nucleic acid. The disease can be treated with supportive measures and, in severe cases, with antiviral drugs such as oseltamivir. In healthy individuals, influenza is typically self-limiting and rarely fatal, but it can be deadly in high-risk groups.
In a typical year, five to 15 percent of the population contracts influenza. There are three to five million severe cases annually, with up to 650,000 respiratory-related deaths globally each year. Deaths most commonly occur in high-risk groups, including young children, the elderly, and people with chronic health conditions. In temperate regions of the world, the number of influenza cases peaks during winter, whereas in the tropics, influenza can occur year-round. Since the late 1800s, large outbreaks of novel influenza strains that spread globally, called pandemics, have occurred every 10 to 50 years. Five flu pandemics have occurred since 1900: the Spanish flu from 1918 to 1920, which was the most severe; the Asian flu in 1957; the Hong Kong flu in 1968; the Russian flu in 1977; and the swine flu pandemic in 2009.
- ^ Cite error: The named reference
krammerwas invoked but never defined (see the help page). - ^ Cite error: The named reference
sauttowas invoked but never defined (see the help page). - ^ Cite error: The named reference
allenwas invoked but never defined (see the help page). - ^ Cite error: The named reference
lampejowas invoked but never defined (see the help page).