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Risk and Complications

The flu is very contagious and can be serious. Getting the flu increases your risk of:

  • Pneumonia
  • Severe flare-up of many health conditions including lung conditions (e.g., asthma, chronic obstructive pulmonary disease)
  • Flu-related hospitalization during pregnancy
  • Bronchitis
  • Ear and sinus infections
  • Dehydration

Risk factors

Factors that increase your risk of getting pneumonia include:

  • Cigarette smoking
  • Chronic lung disease (e.g., chronic obstructive pulmonary disease, asthma, bronchiectasis, cystic fibrosis) or other chronic diseases (e.g., heart, kidney, liver, anemia, diabetes)
  • Very young (less developed immune system) and very old (less effective immune system)
  • Residents of a nursing home or other chronic care facility
  • Being a patient in a hospital
  • “Aspiration pneumonia” can occur when something is aspirated (inhaled) into the lungs. This can be due to:
    • Brain dysfunction (e.g., dementia, stroke, brain injury) increasing the risk that you will aspirate food
    • Overdose of alcohol or drugs increasing the risk that you will aspirate vomit
  • Weakened immune system (e.g., HIV/AIDS, taking corticosteroid pills, organ transplant, being treated for cancer)
  • Recent surgery


It’s important to see your health-care provider for treatment as soon as possible to help prevent any complications. Pneumonia can be life-threatening—it’s a leading cause of death and hospitalization in seniors and in people with chronic diseases.

When your lungs become infected, the alveoli fill with pus and mucus, blocking oxygen from getting into your bloodstream. As you work harder to breathe in more oxygen, you can feel short of breath. The swelling and infection also cause many other pneumonia symptoms like cough, fever and chest pain. If your breathing gets very difficult, you may need more intensive hospital care (e.g., oxygen, intravenous medication, ventilator/breathing machine).

If bacteria from your lungs enters your bloodstream, this can cause a very serious infection called bacteremia that can spread to other organs.

When left untreated, pneumonia can cause a pleural effusion (fluid build-up around the lungs) and a lung abscess (cavity filled with pus and mucus).