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What is pneumonia?

  • Pneumonia is caused by infection from bacteria, viruses or fungi. Our lungs are made of lots of little air sacs (alveoli). Pneumonia causes these to become inflamed and fill with fluid.1
  • ​​​​The most common cause of community acquired pneumonia is a bacteria called Streptococcus pneumoniae.1,2
  • ​​​​​​Viruses causing pneumonia can be spread from person to person through physical contact, coughing and sneezing.3

  • Find out more information on how you can help protect your loved ones on the NHS website.4

Symptoms of pneumonia

While pneumonia can make you feel very unwell, symptoms vary and people often confuse it for cold or flu.4,5 A healthcare professional can diagnose pneumonia through a physical exam and tests.3

How do you catch pneumonia?

There are different types of pneumonia, with the two most common being bacterial and viral.1 The various causes of pneumonia are listed below.

Flu is one of the most common causes of viral pneumonia in adults, though post-flu complications can also cause bacterial pneumonia.1,6

Bacterial pneumonia causes2

Bacterial pneumonia is caused by different types of bacteria that work their way into the lungs and then multiply. Infections causing bacterial pneumonia can be spread through physical contact, coughing and sneezing.1,2

  • The most common cause of bacterial pneumonia is a pneumococcal infection, due to bacteria called Streptococcus pneumoniae.1
  • The second most common cause is the bacteria Haemophilus influenzae. The bacterium may live in your upper respiratory tract, only causing harm in those with a weakened immune system.2
  • Mycoplasma pneumonia is a bacteria that can cause atypical pneumonia, also known as walking pneumonia, which can result in mild symptoms similar to a respiratory infection or common cold. 7

Viral pneumonia causes3

There are several viruses which can lead to viral pneumonia, including3:

  • Adenoviruses (representation pictured above), which can also cause the common cold and bronchitis
  • Varicella zoster virus or chickenpox
  • Influenza virus, more commonly known as flu
  • Respiratory syncytial virus, which causes cold-like symptoms

Coughing, sneezing, or touching contaminated surfaces are common ways for viruses to spread.3

Fungal pneumonia causes8

  • Fungal pneumonia usually refers to infections where the fungi invade lung tissue after entering the airways through inhalation.8

  • Some species of fungi are more likely to cause pneumonia, particularly in certain areas or among certain high-risk groups.8
  • Fungal pneumonia is rare in the UK and is more likely to affect people with a weakened immune system.4

  • There are several types of infections which can lead to fungal pneumonia, including8:

    • Aspergillosis, caused by aspergillus mould
    • Candidiasis, caused by candida fungus
    • Mucormycosis, caused by mucor mould

Why is pneumonia so dangerous?

If you catch it, pneumonia can be serious and life-threatening.1,4

Stethoscope graphic

In 2022-2023, it is estimated that pneumonia was responsible for around 223,277 hospital admissions in England and approximately a fifth of hospitalised pneumonia cases were reported in people aged under 65.9

Heart monitor graphic

Studies have shown that being hospitalised with pneumonia is a risk factor for heart attacks10 and bacterial pneumonia is linked with an increased incidence of stroke episodes in the week following infection.11

Cough graphic

Pneumonia and influenza, combined, is one of the most common causes of death in the UK.12

View References

  1. Asthma and Lung UK. What is Pneumonia. Available at: Last accessed January 2024.

  2. Healthline. Bacterial Pneumonia. Available at: Last accessed January 2024.

  3. Healthline. Viral Pneumonia. Available at: Last accessed January 2024.

  4. NHS. Pneumonia. Available at: Last accessed January 2024.

  5. GoodRx Health. 9 Illnesses That Can Cause Flu-Like Symptoms. Available at: Last accessed January 2024.

  6. Rothberg MB., Haessler SD, Brown RB. Complications of viral influenza. Am J Med. 2008 Apr;121(4):258-64. doi: 10.1016/j.amjmed.2007.10.040.

  7. Healthline. Mycoplasma Pneumonia Infection. Available at: Last accessed January 2024.

  8. Healthhype. Fungal Pneumonia. Available at: Last accessed January 2024.

  9. NHS Digital. Hospital Episodes Statistics for England. Hospital Admitted Patient Care Activity 2022-23. Available at: Last accessed January 2024.

  10.  Corrales-Medina VF., Alvarez KN., Weissfeld LA., et al. Association between hospitalization for pneumonia and subsequent risk of cardiovascular disease. JAMA. 2015;313(3):264-74.

  11. Warren-Gash C., Blackburn R., Whitaker H., McMenamin J., Hayward AC. Laboratory-confirmed respiratory infections as triggers for acute myocardial infarction and stroke: a self-controlled case series analysis of national linked datasets from Scotland. European Respiratory Journal Mar 2018, 51 (3) 1701794; DOI: 10.1183/13993003.01794-2017.

  12. Office for National Statistics. leading causes of death, UK; 2001 to 2018. Available at: Last accessed January 2024.

PP-UNP-GBR-7121 January 2024