What is influenza?
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Influenza is a febrile, acute viral disease of the respiratory tract: nose, throat, bronchial tubes, upper and lower lungs and the middle ear4
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Two clinically relevant types: A and B4
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The ratio of type A to type B influenza isolates varies from year to year
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Prevalence of influenza
Annual influenza attack rates range from 5% to 20% of the U.S. population. Influenza and its complications cause an estimated 36,000 deaths annually, and more than 200,000 people are hospitalized.
Symptoms of influenza
Influenza begins abruptly, often with a fever over 101°F (sometimes higher in children and slightly lower in the elderly). Other classic signs and symptoms include dry cough, headache, muscle pain, chills and/or sweats, sore throat, and potentially severe and persistent discomfort and fatigue. Sensitivity to light or other eye problems, and gastrointestinal distress may also be present. Symptoms may be severe for up to 5 days, and may persist for up to 2 weeks.
Transmission of influenza
The influenza virus usually is passed in droplets shed by an infected person during sneezing or coughing. A person becomes infected by breathing in these droplets. The virus then settles into the entire respiratory system (which includes the nose, sinuses, throat, lungs, and middle ear), and begins replicating 24 hours before symptoms are discovered. An infected person can pass on the disease for four to five days.
Complications with influenza
One of the most severe complications of influenza is pneumonia, which may be a complication of influenza itself or of a bacterial infection accompanying or following influenza. Pneumonia from influenza occurs mostly in patients with cardiovascular disease, chronic lung disease, certain serious forms of anemia, or a weakened immune system, such as those with cancer, HIV/AIDS, or organ transplants. Antibiotics do not help treat this type of pneumonia. Bacterial pneumonia can occur during or after influenza infection and can be treated with antibiotics. Other complications may include otitis media (ear infection), bronchitis, and croup, which can be severe in young children. Chronic conditions such as asthma and cystic fibrosis are worsened by influenza.
Risk factors of influenza
People at highest risk of developing serious complications from influenza are those aged 65 and older or people of any age with chronic diseases of the heart, lungs, or kidneys, and those with diabetes, weakened immune systems, or certain serious forms of anemia. People aged 50 to 64 years are also advised to get annual influenza vaccination because a substantial number of them have one or more chronic medical conditions that place them at high risk for influenza-related hospitalization and death.