What is pneumonia and why can it be so deadly?

Chest x-ray indicating pneumonia In this chest x-ray, the lower half of the right lung (appearing on the left of the image) shows as white, indicating pneumonia

Pneumonia is an inflammation of the lungs, and can be life-threatening, especially among the elderly and those with serious underlying health conditions.

What causes pneumonia?

Pneumonia is usually caused when particular germs - bacteria, viruses or fungi - infect the lungs.

Normally, your body is able to filter most germs out of the air you breathe and stop infections from reaching the lungs. But even if germs do make it through to the lungs, or an infection spreads from another part of the body, a healthy person's body will be able to deal with the problem.

Bacteria that cause pneumonia

  • Bacteria need moisture and warmth to live - for which the human body is an ideal host
  • One of the most common pneumonia-causing bacteria is Streptococcus pneumonia or Pneumococcus for which there is now a vaccine
  • Other common ones include the bacteria haemophilus and staphylococcus
  • More unusual bacteria are sometimes found, especially in people with underlying problems with their immune systems

As pneumonia spreads through the lungs, the body fights back. White blood cells attack the germs. The infected area becomes inflamed - part of the body's normal response to infection.

In a healthy person, these natural defences will overcome the pneumonia. But in someone with a weak immune system, the infection cannot be contained.

At the ends of the breathing tubes in the lungs are the tiny air sacs where oxygen passes into your blood - the alveoli. As these become infected, they start to fill up with fluid and pus.

This disrupts the normal process of gas exchange in your lungs, and stops oxygen from reaching the blood stream as well as causing a rise in blood levels of the waste gas carbon dioxide, which cannot be so easily removed. As a result the person becomes short of breath.

If left untreated, oxygen levels can fall to life-threatening levels. If the body's tissues - especially in the heart and brain - do not get the oxygen they need, confusion, coma, heart failure and eventually death may result.

Bacterial pneumonia is usually more serious as it causes more severe symptoms. However, viral pneumonia caused by the flu virus can be life-threatening as well if it triggers a particularly severe inflammation of the lungs or is complicated by a secondary bacterial infection.

Who is most at risk?

Anybody can be affected by pneumonia but for some it can be far more serious. This is because healthy people tend to fight off viral pneumonia on their own or successfully battle bacterial pneumonia with the aid of antibiotics.

However, those with chronic disease (especially lung disease such as Chronic Obstructive Pulmonary Disease, or heart disease) or compromised immune systems are less likely to respond to treatment, less able to cope with the stress on the organs caused by pneumonia and more likely to develop serious complications. This is why it is still a leading cause of death among the elderly and seriously ill.

When is pneumonia most likely to strike?

  • In the UK, pneumonia affects around one in 100 adults each year
  • Viral infections that are common in winter, such as flu, can increase the risk of pneumonia
  • Pneumonia is therefore most likely to strike in the colder months of autumn and winter
  • Pneumonia can affect people of any age, although it is more common in infancy and among the elderly

Source: NHS Choices

A weakened immune system can be caused by many factors including age, illness and disease. The following are included in this category:

  • Babies and infants
  • Older people
  • People with long-term heart, lung and kidney diseases
  • Those with diabetes
  • People with cancer, especially those receiving chemotherapy or who have leukaemia or lymphoma
  • People who smoke and those who drink alcohol to excess
  • People receiving drugs that suppress the immune system to treat an existing illness
  • People with HIV/AIDS

For more information on symptoms and treatment, visit NHS Choices

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