Influenza (commonly called the flu) is a highly contagious illness that can occur in children or adults of any age. This illness is caused by the influenza viruses that infect the nose, throat, and sometimes the lungs. It can cause mild to severe illness, and at times can lead to death. The best way to prevent the flu is by getting a flu vaccine each year.
There are three different types of flu viruses: influenza A, B, and C, all of which cause illness in humans. Influenza is a virus that actually has hundreds of different strains. The virus mutates frequently, but the strains are classified into one of three main categories—A, B, or C. Influenza A is the group that most commonly causes illness in humans.
All Influenza A viruses are further broken down into H and N subtypes. So, any influenza virus that is described as “H#N#” (such as H1N1) is an influenza A virus. There are 16 H subtypes and nine N subtypes, but only three combinations have actually caused highly contagious illness in humans. The three combinations that cause almost all outbreaks of the flu in humans are H1N1, H2N2 and H3N2.
Even in these subtypes, the influenza virus can mutate and change each year. For this reason, influenza viruses are also named using the host of origin (swine, chicken, etc., or no host if it is of human origin), the geographical location of origin (Hong Kong, Alberta, etc.), strain number, year of discovery (or isolation).
Influenza B is less common but still causes outbreaks of seasonal flu. One or two strains of influenza B are included in the seasonal flu vaccine every year to protect people from the strains.
How Flu Spreads
Flu viruses spread mainly by droplets made when people with a flu cough, sneeze or talk. These droplets can land in the mouths or noses of people who are nearby. Less often, a person might also get flu by touching a surface or object that has flu virus on it and then touching their own mouth, eyes or nose.
Period of Contagiousness
Most healthy adults may be able to infect other people beginning 1 day before symptoms develop and up to 5 to 7 days after becoming sick. Children may pass the virus for longer than 7 days. Symptoms start 1 to 4 days after the virus enters the body.
Symptoms of Flu
- Fever* or feeling feverish/chills
- Sore throat
- Runny or stuffy nose
- Muscle or body aches
- Fatigue (very tired)
- Some people may have vomiting and diarrhea, though this is more common in young children than in adults.
- Adequate Rest
- Fluids – Drink enough fluids so that you do not become dehydrated.
- Paracetamol can relieve fever, headache, and muscle aches. Aspirin and medicines that contain aspirin are not recommended for children under 18 because it can lead to a serious disease called Reye syndrome.
- Antiviral medications, such as Tamiflu, that may help shorten the duration of the illness. However, Tamiflu is only effective if taken within the first 48 hours of the onset of symptoms.
- Antibiotics are not generally used unless there is a secondary bacterial infection or other complications.
Complications of Flu
Complications of flu can include bacterial pneumonia, ear infections, sinus infections, and worsening of chronic medical conditions, such as congestive heart failure, asthma, or diabetes.
Preventing Seasonal Flu:
The”flu shot”–an inactivated vaccine (containing a dead virus).The seasonal flu shot is approved for use in people 6 months of age and older, including healthy people, people with chronic medical conditions and pregnant women.
About two weeks after vaccination, antibodies develop that protect against influenza virus infection. Flu vaccines will not protect against flu-like illnesses caused by non-influenza viruses.
The seasonal flu vaccine protects against the three influenza viruses that research suggests is the most common.The vaccine usually protects 50 to 80 percent of those who are vaccinated from getting the flu. If you get the flu after being vaccinated, your symptoms are likely to be milder and last for a shorter time compared with people who were not vaccinated.
Infection control measures, like handwashing and covering your mouth when you cough, can help to prevent the spread of influenza
When to Get Vaccinated Against Seasonal Flu
Yearly flu vaccination should begin in September, or as soon as vaccine is available, and continue throughout the flu season. While flu season can begin early as October, most of the time seasonal flu activity peaks in January or later.
People at High Risk from Flu
- Children younger than 5, but especially children younger than 2 years old
- Adults 65 years of age and older
- Pregnant women (and women up to two weeks postpartum)
- Residents of nursing homes and other long-term care facilities
- Health care workers
- People who have medical conditions including:
- Chronic lung disease (such as chronic obstructive pulmonary disease [COPD] and cystic fibrosis)
- Endocrine disorders (such as diabetes mellitus)
- Heart disease (such as congenital heart disease, congestive heart failure and coronary artery disease)
- Liver disorders
- Kidney disorders
- Blood disorders (such as sickle cell disease)
- Immunosuppression, including HIV infection (particularly if CD4 <200 cells/microL), organ or hematopoietic cell transplantation, inflammatory disorders treated with immunosuppressants
- Neurologic disorders that can compromise handling of respiratory secretions (eg, cognitive dysfunction, spinal cord injuries, seizure disorders, neuromuscular disorders)
- People who are morbidly obese (Body Mass Index (BMI) of 30 or greater)
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