Infectious diseases


Last update: 16-01-2023

How else can it be called?

  • Flu

  • ICD-10: J11

What is influenza?

Influenza, commonly known as the flu, is a contagious viral disease caused by the influenza virus that it is transmitted when people cough or sneeze or by contact with contaminated objects.

Sometimes the term flu refers to any type of upper respiratory tract infection. But the flu is more than just a simple cold and very contagious. There is usually an annual flu epidemics, usually in winter.

The flu is caused by a virus that can mutate relatively easily. For that reason, the virus each season will be probably different from the one of the previous seasons and, therefore, the immune system cannot recognize it as a threat.

What are the main symptoms of influenza?

The main symptoms, in addition to a general malaise, are:

  • Chills
  • Fever up to 40ºC (104ºF)
  • Sneezing
  • Cough
  • Headache
  • Muscle ache
  • Sore throat

The fever usually lasts from three to five days. The total recovery, if there are not additional complications, usually takes one to two weeks.

What is the recommended treatment?

There is currently no medical treatment to cure the flu but it is possible to relieve common flu symptoms with medication (antipyretic, analgesics, etc.).

The flu is a viral infection and that is why antibiotics are not effective. The use of antibiotics can lead, in addition, to antibiotic resistance. Antibiotics, in case of suffering from the flu, only should be used under medical prescription to treat or prevent complications in concrete cases.

In cases of high-risk patients or complications, it may be necessary hospital management with antiviral treatment and oxygen therapy depending on each case.

Which measures can help reduce symptoms?

There are some tips that can help reduce the symptoms:

  • Get plenty of rest.
  • Take an analgesic to relieve the symptoms, as long as there are no contraindications.
  • Drink plenty of water and juices.

The flu is very contagious and it spreads by breathing in air when an infected person coughs or sneezes or just by physical contact. For that reason, it is necessary to cover the mouth and nose when coughing or sneezing and to keep hands clean.

If you are infected with the flu and live with people in high risk of suffering respiratory diseases you must wear a mask and avoid contact with them. For example:

  • Elderly people
  • People with chronic diseases or immunosuppression

It is also helpful to clean any surface that may be contaminated with respiratory droplets.

How can I prevent it?

There is a seasonal flu vaccination. The WHO (World Health Organization) recommends the vaccination of the following high risk groups:

  • Children from six months to five years
  • Elderly people over 65 years of age
  • People with chronic disease (asthma, high blood pressure, diabetes, obesity)
  • Immunocompromised people (with a weak immune system)
  • Pregnant women or women who want to become pregnant
  • People who live in a retirement home or crowded places
  • People who are prone to be infected: retirement home workers, doctors, nurses

When it is necessary to go to the doctor?

If you are infected, it is necessary to contact your doctor in case of:

  • The treatment for the fever is not effective
  • Feeling breathing difficulty at rest
  • You are in a high-risk group
  • If you experience any symptom that you do not think is related with a normal flu, or the symptoms of the flu are too intense
  • If you keep on coughing for more than ten days
Medically reviewed by Yolanda Patricia Gómez González Ph.D. on 16-01-2023


  • Diagnostic Pathology of Infectious Disease. 2nd edition. Richard L. Kradin. 2018. ISBN: 978-0-323-44585-6. Pág. 81.
  • Influenza (Seasonal). World Health Organization. (12 January 2023). Available on:
  • Harrison's Principles of Internal Medicine, 20 edition (2018). Chapter 195: Influenza Pág. 3624. McGRAW-HILL. ISBN: 978-1259644030.

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