Influenza A (H1N1)

"It runs and is treated like the common flu but with a higher fever".


Influenza A is an infectious disease caused by a type A influenza virus, belonging to the family orthoymyxoviridae, which primarily affects swine populations. Its morbidity is usually high and its mortality low (1-4%).

The most common viruses are H1N1, although other viruses, such as H1N2, H3N2, and H3N1, also circulate among animals. These viruses can spread among pigs throughout the year, but most infectious outbreaks occur in the late fall and winter months, as do outbreaks in people.

What are the symptoms of influenza A?

The symptoms are similar to those of a common flu.

  • Fever greater than 38° C, with a sudden onset with temperature greater than 39° C.
  • Frequent and severe cough.
  • Headache.
  • Lack of appetite.
  • Nasal congestion.
  • General discomfort.
  • Digestive symptoms: nausea, vomiting and/or abdominal pain.

An untreated influenza pattern or associated with other uncontrolled disease can lead to complications, mainly respiratory (otitis, sinusitis, rhinitis, pneumonia, bronchopneumonia, obstructive laryngitis), cardiac or even death, this is often seen when large outbreaks or epidemics occur.

Children need to be monitored because if they are treated with aspirin they may develop encephalitis.

Learn about Influenza A and how it is transmitted (available in spanish)

The most common symptoms are:

  • Fever greater than 38° C.
  • Frequent and intense cough.
  • Headache.
  • Lack of appetite.
  • Nasal congestion.
  • General discomfort.
  • Nausea, vomiting and/or abdominal pain.

Do you have any of these symptoms?

You may have influenza A

What are the causes of influenza A?

Influenza viruses can be transmitted directly from pigs to people and from people to pigs.

Human infections with influenza viruses from pigs are more likely to occur in people who are in close contact with infected pigs.

Person-to-person transmission of swine influenza can also occur, primarily when persons infected with influenza virus cough or sneeze. People can become infected by touching something with influenza virus on it and then putting their hands to their mouth or nose.

It is highly contagious (3-7 days once symptoms begin) and most likely to occur indoors. Influenza A is not spread to people by eating properly processed or prepared pork or other pork products. The swine flu virus is killed by cooking at temperatures of 70º C.

How is it prevented?

  • If possible, it is advisable not to travel to areas declared to be at risk.
  • Avoid close contact with infected people.
  • Do not share food, cups and cutlery.
  • Cover your mouth and nose with a tissue when you cough or sneeze. Throw the tissue in the trash after you use it.
  • Ventilate closed areas. Keep your home clean.
  • Wash your hands often with soap and water.
    If you have a sudden high fever, cough, headache, muscle and joint pain, see your doctor.

How is influenza A diagnosed?

To diagnose type A swine influenza infection, a respiratory tract secretion sample should generally be collected within the first 4-5 days of illness (when an infected person is most likely to spread the virus).

However, some people, especially children, may spread the virus for 10 days or more.

Influenza A in humans is treated with the same supportive measures and medications as regular flu.

How is influenza A treated?

There are two classes of these drugs: the adamantanes (amantadine and rimantadine) and the neuraminidase inhibitors (oseltamivir and zanamivir), but they must always be used under a doctor's prescription.

Although most swine influenza viruses have been sensitive to all four types of drugs, the seven most recent swine influenza viruses isolated from people are resistant to amantadine and rimantadine.

CDC currently recommends the use of oseltamivir or zanamivir for the prevention and treatment of infection with swine influenza viruses. It is important to quickly identify patients with suspected disease in order to initiate treatment, as the efficacy of these drugs is significantly greater when started early.

Influenza A vaccine is now available. The groups at risk to be vaccinated first will be healthcare workers - including nursing home workers -, essential service workers, pregnant women and chronically ill people from six months of age.

A single dose of vaccine is sufficient for those over 2 years of age. In some cases, a second dose is required for children under 2 years of age. The vaccine leaves permanent immunity against the virus.

Where do we treat it?


The Infectious Diseases Service
of the Clínica Universidad de Navarra

This area works on the diagnosis and treatment of diseases produced by an infectious agent, which can be bacteria, virus, fungus and protozoa. Infections affect people by causing very different processes that can be located in any tissue of the human body, so it requires a specific approach.

This area carries out its activity on three fronts: care work, focused on the diagnosis and treatment of infectious diseases; teaching, with training of medical students, resident doctors and nurses; and research vocation, through the development of clinical and laboratory studies.

Organized in care units

  • Infections associated with biomaterials.
  • Nosocomial infections (multi-resistance).
  • Infections in immunosuppressed patients.
  • Community infection.
  • Traveler's medicine.
  • Prudent use and optimization program of anti-infective therapy.
  • Control of infection by multi-resistant microorganisms.
Imagen de la fachada de consultas de la sede en Pamplona de la Clínica Universidad de Navarra

Why at the Clinica?

  • We perform the traveler's assessment and analytical tests in less than 24 hours.
  • Second opinion consultation when the infection has not yet been resolved.
  • We ensure the prudent use of antibiotics.