What is the cause of pneumonia?

This factsheet is for people who have pneumonia or for people who want information about pneumonia.

Pneumonia is an inflammation of the lungs, usually caused by an infection of the lung tissue by one of many different microorganisms (germs). It is very common in the UK - it affects around 1 in every 100 people each year. Babies and people over 65 most commonly get pneumonia and most infections occur in the autumn or winter.

Most types of pneumonia can usually be treated effectively with antibiotics. However it can also be a serious illness, especially for people who are elderly and frail or already ill.

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Types of pneumonia
Pneumonia is often divided into two main categories ('community-acquired pneumonia' and 'hospital-acquired pneumonia') depending on whether you were infected while living at home (in the community) or while staying in hospital.

There are different types of pneumonia within these categories caused by various infections, which are described below.

Typical pneumonia
There are a range of bacteria that may cause an infection leading to 'typical pneumonia' including Streptococcus pneumoniae which causes pneumococcal pneumonia. This is the most common cause of pneumonia.

Viruses can also be a source of infection including influenza - or flu.

An infection with a bacterium and a virus can occur at the same time. A Streptococcus pneumoniae infection is usually 'secondary' to a person having flu for example. This is known as a 'secondary infection' and can slow down recovery significantly.

Atypical pneumonia
Less commonly, microorganisms can cause other forms of pneumonia. These illnesses are classed as "atypical pneumonia" and include:

Legionnaire's disease (caused by a bacterium)
SARS - severe acute respiratory syndrome (caused by a virus)
Weakened immune system
People with a weakened immune system (such as people with AIDS or those that have had an organ transplant and are taking immunosuppressant drugs) may get additional pneumonia-causing infections.

These include an infection with the fungus-like organism Pneumocystis carinii. This infection is rarely the cause of pneumonia in people who have a fully-functioning immune system.

Aspiration pneumonia
Pneumonia can also be caused by inhaling substances, such as caustic chemicals, food or vomit into the lungs. This is known as "aspiration" pneumonia and is not infectious.

Symptoms
Your symptoms will depend on how much of your lung is affected and the type of infection that you have. Symptoms may come on quite suddenly and include:

in the beginning, a dry cough, which progresses to be a cough with phlegm that is often green/yellow or rust-coloured and may be smelly
breathlessness
pain in the side of your chest that can make breathing and coughing uncomfortable
fever
loss of appetite
aches and pains
Complications
Complications are more common in older people and may include:

a build up of fluid around the lungs called a pleural effusion
breathing difficulties, which will need treatment in hospital
spread of the infection to your blood, called septicaemia or "blood poisoning" - this can be very dangerous
How do you get pneumonia?
The microorganisms (germs) that cause pneumonia may be present in your body for some time before causing illness. Or, they may also be spread between people through droplets in the air. Coughing and sneezing create droplets.

There are a number of factors that affect your body's ability to fight off infection and put you more at risk of developing pneumonia. They include:

being in poor health
age - the very young and old (over 65) are most susceptible to pneumonia
smoking (as smoking damages your lungs which makes it easier to get an infection)
heavy drinking
heart disease
having a lung disease, such as asthma or chronic obstructive pulmonary disease (COPD)
a low immunity to infection - if you have an illness such as AIDS or are having some types of chemotherapy for example.
Hospital-acquired pneumonia
People in hospital are vulnerable to pneumonia for a number of reasons. These include:

having a weakened immune system, which increases your risk of getting pneumonia
a reduced cough reflex following surgery or severe illness - a cough reflex is the body's way of clearing things out of the airways that may irritate them, an automatic reaction that defends the body against infections
the types of bacteria responsible for pneumonia caught in hospital, which tend to be different from those that cause community-acquired pneumonia - they may also be resistant to the standard antibiotics (such as resistant strains of the bacterium Staphylococcus aureus)
Diagnosis
Your doctor will examine you and ask you about your symptoms. He or she will tap on your chest and listen to how your breath sounds with a stethoscope.

Your doctor may suggest that you have an X-ray to determine the location and extent of the infection.

Your doctor may take a sample of blood or phlegm for testing. The sample will be sent to a laboratory for examination to find out what type of infection you have. This will help your doctor to decide how to treat you.

Treatment
If you have pneumonia you should drink plenty of fluids. If you have pain you should take painkillers that you would normally take for a headache.

Drug treatments
If you have community-acquired pneumonia, your doctor will prescribe you antibiotics immediately, often prior to tests on the phlegm sample. Antibiotics treat pneumonia caused by bacteria. Antibiotics are usually given straight away as bacterial infections are the most common cause of pneumonia and antibiotics are generally very effective. It is usually safe to assume that the infection will respond to standard antibiotics such as amoxicillin. Generally for chest infections you should take antibiotics for about seven days and you must complete the full course.

If you have a weakened immune system you may be offered a long-term, daily dose of preventive antibiotics.

If test results show that you have pneumonia caused by a virus, antibiotics will not work and your body will need to fight the infection on its own. It may therefore take longer to recover. However, if you have an infection caused by the chickenpox or herpes viruses, you may be prescribed antiviral drugs if the infection was caught early. You may also need antibiotics if you have a secondary bacterial infection.

If you have fungal pneumonia, you may be given antifungal drugs that you can take as tablets or you may need to take them intravenously.

You should get better at home without needing to go for hospital treatment. Provided you do not have any complications, your symptoms should begin to improve quickly with treatment and generally pneumonia should not cause any long-term damage to your lungs. If you are given drug treatments, let your doctor know if your symptoms do not improve after two days.

Hospital treatment
If you are very ill or your symptoms do not improve after drug treatment, you may need hospital treatment. This is especially important for very young and old people.

The appropriate drug therapy, as well as fluids, will be given to you through a vein (intravenously). To help you breathe, you may be given extra oxygen through a face mask.

Prevention
Stopping smoking and only drinking in moderation can reduce your risk of many illnesses, including pneumonia.

Vaccines
There are immunisations for some infections that can cause pneumonia.

A pneumococcal vaccine can prevent pneumonia caused by Streptococcus pneumoniae infection. There are two pneumococcal vaccines, brand names Pneumovax II and Prevenar. Both of these vaccines are given by injection. This vaccine is recommended to anyone with lung or heart problems and most people only need to have it once. The government plans to introduce this vaccine to the childhood immunisation programme later in 2006 and it is already available to people over 65.
A Haemophilus influenzae type B vaccine ("Hib" vaccine) can prevent you getting flu. This annual vaccination is now given routinely to babies and everybody over age 65, and those with long-term lung, heart or kidney diseases, or with a weakened immune system. You can get vaccinated at your local GP surgery each autumn. Alternatively, they are available from private clinics.