Pneumonia is an inflammation of the lungs that is usually caused by infection. Pneumonia can also be caused by inhaling irritants such as vomit, liquids, or chemicals. With pneumonia, the air sacs in the lungs fill with liquid or pus, which interferes with the lungs' ability to transfer oxygen to the blood.
Before the invention of antibiotics in the 1930s, pneumonia was a leading cause of death. Though it has since become very treatable, pneumonia remains a public health problem.
There are many different kinds of pneumonia, ranging from mild to severe. There are 4 basic types:
Pneumonia rarely causes serious complications for healthy people under 65 years of age. People who suffer from chronic respiratory diseases or who have compromised immune systems are generally at greater risk for developing pneumonia.
The most common causes of pneumonia are infections caused by:
Most types of pneumonia are transmitted in the same way as influenza or the common cold - by people's hands and by tiny droplets from their mouths and noses. In fact, the same viruses that cause colds and the flu can cause pneumonia. If they infect the throat, sinuses, and upper respiratory tract, they cause a cold. If they reach the lungs, they cause pneumonia.
Bacteria that live permanently in many peoples' throats cause some of the more severe types of pneumonia. Normally, the immune system keeps them in check. If someone is weakened by a throat virus, these bacteria can trickle down into the respiratory tract. Bacterial pneumonia is most often caused by the bacteria Streptococcus pneumoniae (pneumococcus).
Respiratory syncytial virus (RSV) is the most common cause of pneumonia in infants and young children. It peaks sharply around December and January and usually isn't a life-threatening disease, though some individuals can be seriously affected. Viruses cause about half of all cases of pneumonia.
Mycoplasma causes the illness called "walking pneumonia," so-called because people who have it are not confined to bed.
A fungus called Pneumocystis carinii is usually seen only in people who have AIDS. This parasite is normally harmless, but in people with HIV it can cause an aggressive and often fatal pneumonia.
In addition to infectious diseases, people can get pneumonia from chemicals that enter the lungs and inflame them. Aspiration pneumonia is caused by accidentally inhaling food, vomit, or digestive acid into the lungs. The inhaled substance may become infected, or it may inflame the lungs and cause them to fill with liquid.
A person who has a higher risk of pneumonia:
Symptoms of pneumonia can vary depending on the cause of the pneumonia and the general health of the person who has pneumonia.
Pneumonia always causes a cough, which often produces sputum. Red-brown, green, or yellow sputum may be a sign of bacterial infection. Thin, whitish sputum is a possible indicator of mycoplasma or viral pneumonia.
In bacterial pneumonia, all or part of the lungs slowly fill with liquid in a process called consolidation. Some bacterial lung infections develop over just a few hours. There's usually a high fever, sometimes going up to 40.9°C (105°F).
Other possible symptoms include:
Viral pneumonias don't actually cause the lungs to fill with liquid; instead, they inflame the actual lung tissue itself. They are usually milder than bacterial infections. An exception is the influenza virus, which can be very serious.
Typically, viral pneumonia causes these symptoms: