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) which then causes the alveoli to fill up with fluid and white cells in an attempt by the body to kill the bugs. When alveoli are filled with fluid and cells, this is called consolidation and this 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 this is called pleurisy.
What causes pneumonia?
The commonest causes of pneumonia are:
- The bacteria Streptococcus pneumoniae (also called the pneumococcus), perhaps responsible for 50% of cases. This bacteria lives in the back of the throat in many people, especially young children, and from there on rare occasions get into the lungs and causes an acute pneumonia which can be severe. Fortunately, this bug is generally readily killed by penicillin and other antibiotics. It often causes pleurisy.
- 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 produced by coughing from people already infected with one of these bacteria. They do not respond to penicillin-type antibiotics, but are killed by macrolides, such as clarithromycin, and by tetracyclines.
- Viruses such as influenza. Viruses, like Mycoplasma and Chlamydia, 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. In 2020 and 2021, COVID-19 used to cause a particularly severe pneumonia but, now everyone has either been vaccinated against COVID or had COVID (or both), it is rare for COVID to cause pneumonia.
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 infections that can cause pneumonia both in normal and immunocompromised patients.
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 between the lungs and ribs, and this is called an empyema. Treating an empyema may need insertion of a tube or even surgery to drain the infected fluid, along with a more prolonged course of antibiotics (up to 6 weeks).
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, the recommendation is that the elderly (over 65 years) and people with chronic diseases affecting the chest, kidneys, liver or brain should be vaccinated with one of the pneumococcal vaccines as they have an increased risk of pneumonia. They also need annual vaccinations against influenza, and those aged 75 to 80 years are eligible for a vaccine that prevents infections with another respiratory virus that is similar to flu called RSV. 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.
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. He is a member of the Joint Committee on Vaccination and Immunisation advising the government on vaccination policy (including vaccines for pneumococcus, influenza, RSV and COVID-19). Recently, this committee has suggested adults could receive an improved vaccine against pneumococcus called PCV20 as an alternative to the existing vaccine (called Pneumovax); this may potentially change which vaccine is used from next year.
Visit our research pages for more information on our research.
See how your donations have contributed to our groundbreaking research
2024 ILD Research Report
Sign up!
Receive our latest research updates and news