What is pneumonia?

Pneumonia is an infection of the deep parts of the lungs called the alveoli. 

This is where oxygen is transferred into the blood from the air, but during pneumonia the alveoli are invaded by bacteria (eg the pneumococcus) or viruses (eg influenza or COVID-19) which then causes the alveoli to fill up with fluid and white cells in an attempt by the body to kill the bugs.  Alveoli filled with fluid and cells is called consolidation and shows up on the X-ray, and is also why patients with pneumonia become breathless as there is less lung available to transfer oxygen into the blood.  If the pneumonia spreads to affect the edge of the lung, then it can inflame the membrane that covers the lung called the pleura. This causes a lot of pain, especially on breathing in, and is called pleurisy.

What causes pneumonia?

The commonest causes of pneumonia are:

  1. The bacteria Streptococcus pneumoniae (also called the pneumococcus), responsible for 50% of cases perhaps. This bacteria lives in the back of the throat in many people, especially young children, and from there very rarely gets into the lungs and causes an acute pneumonia which can be severe. Fortunately, this bug is readily killed by penicillin and other antibiotics. It often causes pleurisy.
  2. Mycoplasma pneumoniae and Chlamydia pneumoniae, which are causes of generally a milder pneumonia accounting for maybe 25% of cases in total. These bacteria are spread by inhaling droplets from people with acute infections. They do not respond to penicillin-type antibiotics, but are killed by macrolides, such as clarithromycin, and by tetracyclines.
  3. Viruses such as influenza. Viruses, like Mycoplasma and Chlamydia, and COVID-19 transfer between people by droplet spread (ie. after someone sneezes). They can cause pneumonia by themselves (termed a primary viral pneumonia) or allow a bacteria such as pneumococcus to reach the alveoli and cause a secondary bacterial pneumonia. COVID-19 causes a particularly severe pneumonia, especially in the elderly or people with weakened immune systems.

If someone has a weakened immune system due to drug treatment for cancers or organ transplantation, then there are a large number of other bugs that can cause pneumonia, the most important of which are the fungi Aspergillus and Pneumocystis, or a virus called cytomegalovirus. In addition, there are a very large number of rare causes of pneumonia both in normal and immunocompromised patients.

What are the symptoms of pneumonia?

The main symptoms are cough, sputum production, fever, and feeling generally ill, sometimes with shortness of breath and chest pain on breathing in.  Usually, the symptoms have only lasted for a few days or a week or two, but can be longer with the more unusual causes.  COVID-19 causes a more prolonged pneumonia lasting 1 to 3 weeks. Most patients with pneumonia have mild disease and so can be treated out of hospital, but in a minority it can be a very severe infection and require admission to hospital or even the intensive care unit.

How is pneumonia diagnosed?

By identifying the combination of evidence of infection with new consolidation – consolidation is recognised either by seeing it on the chest X-ray or hearing abnormalities on listening to the lung.  We try to find which bug is causing the pneumonia by sending sputum, throat or nose swabs, and blood or urine samples to the laboratory for special tests.

Can pneumonia be treated?

Yes, with antibiotics to kill the bug and by giving the patient additional oxygen to boost the oxygen level in the blood. Most bacteria are killed readily by antibiotic treatments, although antibiotic resistance can be a problem on occasions. Some viruses and fungi are actually quite hard to kill with antibiotics, but these infections are rare unless someone has a weakened immune system.  Pneumonia occasionally can lead to infection of the surface of the lung, called empyema, and this may need insertion of a tube to drain the infected fluid or even surgery. COVID-19 causes the immune system to over-react to the presence of the virus leading to more lung inflammation than is needed to kill the virus; it is treated with drugs that reduce the inflammatory response to the viral infection including dexamethasone, a steroid.

Living with pneumonia

Pneumonia is an acute infection from which most patients will make a rapid recovery. Many patients do suffer from easily getting tired for a couple of months after having had pneumonia, but this gradually improves.  Amazingly, even with severe pneumonia, the lung usually recovers and has no lasting damage, although occasionally there might be some scarring of the lung (rarely leading to bronchiectasis) or lung surface (the pleura). At present, we do not know whether the lung damage caused by COVID-19 recovers completely or leaves some degree of mild damage that might make some people more breathless when doing everyday activities such as carrying shopping or doing the cleaning.

At present, the recommendation is that the elderly (over 65 years) and people with chronic diseases affecting the chest, kidneys, liver or brain should be vaccinated against the pneumococcus with the Pneumovax vaccine as they have an increased risk of pneumonia.  Smoking also increases the risk of developing pneumonia, and if someone has had one episode of pneumonia, they should stop smoking to help prevent another.  Children in the UK are now automatically vaccinated as infants against infections with the pneumococcus with the Prevenar vaccine. All adults should get the COVID-19 vaccine.

Ongoing research into pneumonia

At UCL, Professor Brown leads an internationally recognised research group into the pneumococcus aiming to identify why it can cause pneumonia, and to develop new vaccines or other treatments to prevent pneumonia.  The research is mainly laboratory-based and has been funded by the Medical Research Council, the Wellcome Trust as well as local charities. His group has published multiple research papers on pneumonia or the pneumococcus, including recent papers describing new methods of trying to prevent infections using novel vaccine approaches.

In addition, Professor Brown is an author on a scientific textbook describing how the pneumococcus is capable of causing pneumonia that was published in 2015, was part of the committee that wrote the National Institute for Clinical Excellence pneumonia guidelines published at the end of 2014, and is a member of the Joint Committee on Vaccination and Immunisation advising the government on vaccination policy (including vaccines for pneumococcus and COVID-19).

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