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. Types A influenza infection can be serious and cause widespread outbreaks and disease.

Common symptoms of type A infection can be confused with other conditions. While in some milder cases the flu can resolve on its own without significant symptoms, severe cases of type A influenza can be life-threatening.

Unlike a common cold, the flu typically 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:

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 throughout the flu season compared to type A.

Humans are the natural host for type B infection. Type B viruses mutate much slower than type A infections and are categorized by strains, but not subtypes. The B virus strains take longer for their genetic makeup to change than influenza A. This drastically reduces the risk of a widespread pandemic due to type B influenza.

Type A influenza can be dangerous and is known to cause outbreaks and increase your risk of disease. Unlike a type B infection, type A viruses are categorized by subtypes and strains. Influenza A mutates faster than influenza B, but both 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 and bird flu. This infection can also spread to other animals and humans. This, combined with the ability of type A influenza to mutate faster than type B, can cause 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 aren’t always accurate, and your doctor may have to make a diagnosis 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 antiviral medication to fight the infection.

Common antiviral prescriptions include:

These medications, known as neuraminidase inhibitors, reduce the ability of the influenza virus to spread from cell to cell, slowing down the infection process.

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.

A new medication called baloxavir marboxil (Xofluza), created by a Japanese pharmaceutical company, was approved in October 2018 by the U.S. Food and Drug Administration (FDA). This antiviral drug helps stop the influenza virus from replicating.

Over-the-counter medication therapy 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’re 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 even longer after you begin experiencing symptoms. This number can fluctuate if your immune system is weak or undeveloped, specifically in cases of children or older adults.

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.

Don’t self-diagnose your condition. The flu can resemble the common cold, but may trigger worsening symptoms. If you think you’ve contracted influenza, schedule a visit with your doctor to discuss treatment.