Influenza — also known as the flu — is a contagious viral infection that attacks your respiratory system. Influenza viruses that infect humans can be classified into three main groups: A, B, and C. Type A influenza is the most serious and known to cause widespread outbreaks and diseases.

Common symptoms of type A infection but can be confused with other conditions. While in some milder cases the flu can resolve on its own, severe cases of type A influenza can be life-threatening.

Unlike a common cold, the flu occurs with a sudden onset of symptoms. Common signs of an influenza infection include:

Sometimes, influenza A symptoms may resolve on their own. However, if symptoms persist for more than a week without improvement, schedule a visit with your doctor. In rare cases, the flu can be deadly.

Left untreated, the flu can cause:

Influenza A vs. influenza B

Types A and B influenza are the more common forms of this infection, routinely causing seasonal outbreaks. Type C influenza usually only causes mild respiratory infections.

Type B influenza can be just as severe as type A influenza but is less common. Type B viruses mutate much slower than type A infections and are categorized by strain. The virus strain changes only every few years. Humans are the natural host for type B infection. This drastically reduces the risk of a widespread pandemic.

Type A influenza is the most dangerous, known to cause outbreaks and increase your risk of disease. Unlike a type B infection, type A viruses are categorized by strain and subtype. These viruses are always changing, creating new strains from one flu season to the next. Past flu vaccinations will not prevent infection from a new strain.

Wild birds are the natural hosts for a type A virus (also called avian flu or bird flu), but this infection can also spread to other animals and humans. This often causes pandemics.

Before treating your condition, your doctor will need to check for the influenza virus. The most commonly used test is the rapid influenza diagnostics test. In this procedure, your doctor swabs your nose or throat. The test will detect virus antigens within 30 minutes or less.

Results are not always accurate, and your doctor may have to diagnose you based on your symptoms or other flu tests.

In some cases, influenza A symptoms can clear on their own with ample rest and fluid intake. In other cases, your doctor may prescribe you antiviral medication to fight the infection.

Common antiviral prescriptions include:

Though effective, these medications can cause side effects such as nausea and vomiting. If you begin to experience any of these symptoms or if your condition worsens, stop using the prescription and visit your doctor immediately.

Over-the-counter medication can also ease flu symptoms. Be sure to stay hydrated to loosen mucus in your chest and strengthen your immune system.

How long is it contagious?

If you have the flu, you are contagious from at least a day before you begin to experience symptoms up through five days after your symptoms begin.

In more severe cases, you could be contagious for up to 10 days after you begin experiencing symptoms. This number can fluctuate if your immune system is weak or undeveloped, specifically in cases of children.

The best way to prevent the flu is through annual vaccinations. Each flu shot protects against three to four different influenza viruses within that year’s flu season.

Other ways to prevent spreading this disease include:

  • washing your hands regularly
  • avoiding large crowds, specifically during a flu outbreak
  • covering your mouth and nose when you cough or sneeze
  • staying home if you develop a fever and for at least 24 hours after it goes away

Type A influenza is a contagious viral infection that can cause life-threatening complications if left untreated. While some cases of this infection can improve without prescribed medication, a visit to your doctor is recommended.

Do not self-diagnose your condition. The flu can resemble the common cold, but may trigger worsening symptoms. If you worry you have been infected with influenza, schedule a visit with your doctor to discuss treatment.