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Influenza is an acute disease of the respiratory system

What is the flu?

Influenza is an acute respiratory disease caused by influenza viruses. There are three types of influenza viruses, A, B, and C. Type A or B viruses are the main causes of influenza in humans, while cases of influenza caused by type C viruses are very rare. Influenza viruses attack the upper and/or lower part of the respiratory system (nose, pharynx, larynx, bronchi). In everyday language the term "flu" is often used as a plus of "cold" or "virus" but, in the strict medical sense of the term, "flu" is the disease caused by the above specific viruses.

How is the flu spread?

The flu is spread from one person to another when a sick person coughs, sneezes or talks and spreads the viruses into the air in the form of very small, invisible droplets. Flu viruses are also spread through hands, when someone touches contaminated objects and surfaces and then touches their eyes, nose or mouth. Factors such as cold weather and crowding (the gathering of many people in closed spaces) increase the transmission of influenza. To prevent transmission, people should cover their mouth and nose with a tissue when coughing or sneezing and wash their hands regularly.

For how many days can a person who has the flu transmit it to others?

Adults can transmit the disease from one day before they become ill to 5–7 days after they develop symptoms. Children and severely immunosuppressed patients can be contagious for more than a week.

What are the symptoms of the flu?

Flu symptoms usually start suddenly and include high fever, muscle and joint aches, headache, extreme tiredness, runny nose, sore throat, cough (usually dry). Children can present symptoms from the gastrointestinal tract, such as nausea, vomiting, diarrhea, while in adults these symptoms are rare.

How long do flu symptoms usually last?

Symptoms begin 1–4 days after exposure to the virus and last 2–7 days, but the cough may persist for some time.

Are there other respiratory viruses circulating during flu season?

Yes. During the flu season, there are other viruses that attack the respiratory system and cause similar symptoms to those of the flu. These viruses include rhinoviruses, which are the main cause of the common cold, and respiratory syncytial virus, which is the most common cause of severe respiratory disease in children and one of the leading causes of serious illness or death in older people. Other viruses that can also cause an influenza-like clinical picture are adenoviruses and parainfluenza viruses.

How is the flu different from the common cold?

The common cold is caused by viruses other than flu viruses. Its symptoms are usually milder, limited to the upper respiratory tract (runny nose, sneezing, sore throat), last less, while complications rarely occur.

On the contrary, the flu can cause serious illness and complications that can sometimes be dangerous in some cases.


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