What Causes Flu

The flu, or influenza, is caused by the influenza virus. There are several different strains of the virus that can cause the flu, including influenza A, B, and C. Influenza A and B are the most common strains that cause seasonal flu outbreaks each year. Type A influenza poses the most serious problems for humans. Strains of this type have also been found in birds, pigs, and other animals. Viruses that affect two different species sometimes combine and mix-and-match genetic information to create a new strain that nobody is immune to and for which no vaccine has been prepared.

Most people get the flu when they breathe in tiny airborne droplets from the coughs or sneezes of someone who has the flu. You can also catch the flu if you touch something with the virus on it, and then touch your mouth, nose, or eyes.

Risk factors for contracting the flu include:

  • Close contact with infected individuals: The flu is highly contagious and can spread easily from person to person through close contact.
  • Weakened immune system: Individuals with weakened immune systems and other conditions that make them susceptible to infections such as:
    • Young children under age 2
    • Adults older than age 65
    • People who have chronic illnesses, such as asthma, heart disease, kidney disease, liver disease and diabetes
  • Living in crowded or institutional settings: Living in close quarters with others, such as in college dormitories, nursing homes, or prisons, can increase the risk of contracting the flu.
  • Travel: International travel to areas where the flu virus is more prevalent can increase the risk of contracting the illness.
  • Not getting vaccinated: Not getting vaccinated against the flu increases the risk of contracting the illness and its complications.
  • People with a body mass index (BMI) of 40 or higher
  • Residents of nursing homes and other long-term care facilities
  • People who are pregnant or plan to be pregnant during flu season

It’s important to take steps to prevent the spread of the flu, such as washing your hands frequently, avoiding close contact with others who are sick, and getting vaccinated against the flu each year.