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Pneumonia Causes & Risks


There are three main causes:

  • Bacterial pneumonia—caused by bacteria, most commonly Streptococcus pneumoniae
  • Viral pneumonia—caused by a virus (responsible for half of all pneumonias)
  • Atypical bacterial pneumonia —often called "walking pneumonia but can cause a more serious or potentially fatal pneumonia; caused by:
    • Mycoplasmahis
    • Chlamydias
    • Other tiny infectious agents that have traits of both bacteria and viruses

Other causes of pneumonia include:

Pneumonias are sometimes described by where it was acquired and how you were exposed to it:

  • Community-acquired pneumonia—acquired in the community (eg, at school, work, gym)
  • Nosocomial pneumonia—acquired during a hospitalization
    • Can be very dangerous, especially for patients on a ventilator
  • Aspiration pneumonia —happens when a foreign matter (often stomach content) is inhaled


lung aspiration food
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Risk Factors

Factors that increase your chance of pneumonia include:

  • Age: 65 or older
  • Flu or other respiratory illness
  • Chronic illness, such as heart or lung disease
  • Stroke (aspiration pneumonia due to difficult swallowing)
  • Weakened immune system caused by AIDS or chemotherapy treatment
  • Chronic bronchitis
  • Malnutrition
  • Pregnancy
  • Infants and very young children
  • Alcohol or drug abuse
  • Smoking
  • Chronic exposure to certain chemicals (eg, work in construction or agriculture)

Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition. Copyright © 2023 EBSCO Publishing All rights reserved.

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