Pneumonia

Pneumonia is infection of the lungs.  The infection is in the lung tissue and the tiny air sacs in the lungs where the blood receives oxygen from air that is breathed in.  It is extremely common and can range from a mild illness to a fatal one, especially if the patient is already sick or in hospital.

Pneumonia is not a single disease but refers to many different infections, each caused by a different micro-organism.

Causes and Development

Pneumonia can be caused by viruses, bacteria, fungi or bacteria-like organisms called mycoplasma.  Pneumonia can also be caused by the inhalation of substances into the lungs such as caustic chemicals, food or vomit.  This is known as aspiration pneumonia.

The most common cause of pneumonia in people aged five to 35 years is mycoplasma.  In older adults, the most common causes are bacteria (e.g. pneumococci), which are also a common cause in young infants.

Signs and Symptoms

The common symptoms of pneumonia are a cough with phlegm, fever, chills, chest pain and breathlessness.  However, they may vary greatly in severity and also depend on the type of organism causing the infection.

Bacterial and Mycoplasmal Pneumonia
Mycoplasma pneumonia usually starts with a dry cough and tiredness, followed occasionally by a rash and phlegm production.  Although the symptoms are usually mild, they can last for several weeks.

Pneumococcal pneumonia gives the common symptoms described above, such as the cough, fever and pain on the side of the affected lung.  Streaks of blood may be seen in the phlegm.

The bacterium Legionella pneumophila causes the pneumonia 'Legionnaire's disease'.  It spreads through water and can contaminate air-conditioning systems, which results in outbreaks of the disease.  The infection begins with aches and pains, fever and headache, followed by a cough that eventually produces phlegm.  Although the disease is usually mild, it can be severe, with extreme breathlessness, diarrhea and confusion.  About 20% of people who develop this disease die.

The bacterium Haemophilus influenzae does not cause flu (which is caused by the influenza virus); instead it is a major cause of pneumonia in children below the age of six years.  The pneumonia usually begins with sneezing and a runny nose, and then develops into the common symptoms described above.  In addition, some fluid commonly develops around the lung, called a 'pleural effusion'.  However, the 'type b' strain of the bacterium can cause severe illness such as meningitis and epiglottitis.

Viral Pneumonia
Many viruses can cause pneumonia, including influenza, herpes, measles and chickenpox.  The symptoms vary according to the type and severity of infection, but usually there is a cough, often with phlegm, fever and chills.

Fungal Pneumonia
Fungi can cause pneumonia, but they are relatively rare except in people who have suppressed immune systems (such as those with AIDS).

Diagnosis and Tests

The diagnosis is often obvious to a doctor from the symptoms.  A thorough examination of the chest, which involves tapping the chest and listening with a stethoscope, helps the doctor to locate where the infection is.  A chest X-ray may be carried out to confirm the diagnosis, but it may not show anything at all (relatively common in mycoplasmal pneumonia).  The doctor may also perform blood tests to confirm an infection is present.

The best test is to take some phlegm, examine it under the microscope and try to cultivate the organism that is causing the infection.  This helps establish which antibiotic the bacterium is susceptible to.  This is important (especially for pneumonias acquired in a hospital) because many bacteria are becoming resistant to antibiotics.

Treatment and Prevention

It is important, obviously, to avoid any of the risk factors such as smoking and excessive alcohol.  People who have had major surgery are shown how to do deep-breathing exercises and may be given physiotherapy to help clear mucous.

Most viral pneumonias are not treated with drugs that kill the virus: your body's immune system will usually do the job.  However, in some cases of chickenpox and herpes an antiviral drug may be used early in the course of the disease.

Prognosis

The outcome of pneumonia depends on the type of infection and its severity as well as on the age and general health of the patient.  Generally, however, the use of antibiotics has improved the outcome greatly.