Pneumonia is an infection of one or both lungs that is usually caused by bacteria, viruses, or fungi. Pneumonia can also be caused by the inhalation of food, liquid, gases, or dust. Approximately 50% of pneumonia cases are believed to be caused by viruses and tend to result in less severe illness than bacteria-caused pneumonia. Most pneumonia in the very young is caused by viral infection, including respiratory syncytial virus (RSV). The symptoms of viral pneumonia are similar to influenza symptoms and include fever, dry cough, headache, muscle pain, weakness, and increasing breathlessness.
More than a million people in the United States are hospitalized each year for pneumonia, making it the third most frequent reason for hospitalizations (after births and heart disease). Although the majority of pneumonias respond well to treatment, the infection can still be a very serious problem. Pneumonia kills between 40,000 and 70,000 individuals in the United States each year.
Pneumonia is spread by close person-to-person contact, usually when an infected person coughs or sneezes on another person.
Individuals considered at high risk for pneumonia include the elderly, infants, and those with underlying health problems, such as chronic obstructive pulmonary disease (COPD), diabetes mellitus, congestive heart failure (CHF), and sickle cell anemia. Other conditions that may increase an individual's chance of developing pneumonia include impairment of the immune system, such as found in acquired immunodeficiency syndrome (AIDS), or those undergoing cancer therapy or organ transplantation.
Currently, over three million people develop pneumonia each year in the United States. Although most of these people recover, approximately 5% will die from pneumonia.
Pneumonia is often a complication of a pre-existing condition or infection. Pneumonia is triggered when an individual's defense system is weakened, most often by a simple viral upper respiratory tract infection or a case of influenza.
Pneumonia can be caused by bacteria, viruses, mycoplasma, and fungi.
The onset of bacterial pneumonia can vary from gradual to sudden. In most severe cases, the patient may experience shaking/chills, chattering teeth, severe chest pains, sweats, cough that produces rust colored or greenish mucus, increased breathing and pulse rate, and bluish colored lips or nails due to a lack of oxygen.

Related Terms

Abscess, acquired immunodeficiency syndrome, adenoviruses, AIDS, anthrax, aspiration pneumonia, Bacillus anthracis, bacteria, bacterial pneumonia, cancer, CAP, CHF, chronic obstructive pulmonary disease, community-acquired pneumonia, congestive heart failure, COPD, diabetes mellitus, empyema, fungi, gastroesophageal reflux, herpesviruses, HIV, hospital-acquired pneumonia, HPV, human immunodeficiency virus, human parainfluenza virus, mycoplasm, mycoplasma, mycoplasma pneumonia, Mycoplasma pneumoniae, nosocomial, oxygen, PCP, pleura, pleural, pleurisy, pneumococcal conjugate vaccine, pneumococcal vaccine, Pneumocystis carinii, respiratory syncytial virus, rickettsia, Rocky mountain spotted fever, RSV, SARS, severe acute respiratory distress syndrome, sickle cell anemia, sputum, Streptococcus pneumoniae, trachea, ventilator, viral pneumonia, viruses.

types and causes of pneumonia

The lungs are two spongy organs surrounded by a moist membrane, called the pleura. When an individual inhales, air is carried through the windpipe (trachea) to the lungs. Inside the lungs, there are major airways called bronchi. The bronchi repeatedly subdivide into many smaller airways, called bronchioles, which finally end in clusters of tiny air sacs called alveoli.
The body has mechanisms to protect the lungs from infection. Individuals are frequently exposed to bacteria and viruses that can cause pneumonia, but a body normally prevents most of these organisms from invading and overwhelming the airways.
Bacterial pneumonia: The bacteria Streptococcus pneumoniae, also called pneumococcal pneumonia, is the most common cause of bacterial pneumonia acquired outside of hospitals (also called community-acquired pneumonia). Pneumonia bacteria are present in some healthy throats. The bacteria can multiply and cause serious damage to a healthy individual's lungs, bloodstream, and brain as well, as other parts of the body. If the immune system is weakened, individuals are especially susceptible to pneumonia. Pneumococcal pneumonia accounts for 25-35% of all community-acquired pneumonia. With an estimated 6,000 deaths in the United States yearly, this can be a serious form of pneumonia. Another bacteria, Haemophilus influenzae or H. influenza, can also cause pneumonia.
Bacterial pneumonia can also be considered hospital-acquired pneumonia. Hospital-acquired pneumonia develops at least 48 hours after hospitalization. The most common causes are bacteria such as Staphylococcus aureus.
Viral pneumonia: According to the American Lung Association, about half of all pneumonias are believed to be caused by viruses. More and more viruses are being identified as the cause of respiratory infection, and though most attack the upper respiratory tract, some produce pneumonia, especially in children. Most of these pneumonias are not serious and last a short time.
Infection with the influenza virus may be severe, but the likelihood of death is rare. The virus invades the lungs and multiplies, but there are almost no physical signs of lung tissue becoming filled with fluid. It finds many of its victims among those who have pre-existing heart or lung disease or are pregnant.
Viral conditions that may lead to pneumonia include: influenza virus, respiratory syncytial virus (RSV), severe acute respiratory distress syndrome (SARS), human parainfluenza virus (HPV), adenoviruses, and herpes viruses.
Walking pneumonia: Walking pneumonia is caused by Mycoplasma pneumoniae. Mycoplasmas are the smallest free-living agents of disease in man. Mycoplasma infections generally cause a mild and widespread pneumonia. Mycoplasmas are responsible for approximately 3% percent of all cases of pneumonia. The most prominent symptom of walking pneumonia is a cough that tends to come in violent attacks, but produces only sparse whitish mucus.
Other types of pneumonia: Certain types of fungus, including Histoplasma capsulatum, Coccidioides immitis, Blastomyces dermatitidis, and Paracoccidioides brasiliensis, also can cause pneumonia. Pneumonia caused by fungi is much less common than pneumonia caused by bacteria or viruses. Another type of fungal pneumonia is caused by Pneumocystis jiroveci. Originally, researchers thought a one-cell organism (protozoan) called Pneumocystis carinii caused this disease, but recent research suggests that a fungus called Pneumocystis jiroveci causes the pneumonia. However, the condition is still commonly referred to as PCP. PCP primarily affects acquired immunodeficiency syndrome (AIDS) patients. Certain diseases, such as tuberculosis, can also predispose someone to pneumonia. PCP may be the first sign of illness in many persons with AIDS. PCP can be successfully treated in many cases. It may recur a few months later, but treatment can help to prevent or delay its recurrence.
Other less common pneumonias may be quite serious and are occurring more often. Various special pneumonias are caused by the inhalation of food, liquid, gases or dust, and by fungi. Obstruction of the lungs, such as a tumor, may promote the occurrence of pneumonia, although obstructions are not causes of pneumonia.
Rickettsia (an organism somewhere between a virus and bacteria) causes Rocky Mountain spotted fever, Q fever, typhus, and psittacosis, all diseases that may have mild or severe effects on the lungs.
Chemical exposure, such as to chlorine gas, can cause inflammation and pneumonia. Workers exposed to cattle are at a risk for pneumonia caused by anthrax from the bacterium Bacillus anthracis.
Aspiration pneumonia: Aspiration pneumonia occurs when foreign matter is inhaled into the lungs, most often when the contents of the stomach enter the lungs after vomiting. This commonly happens when a brain injury or other condition affects the normal gag reflex.
Another common cause of aspiration pneumonia is consuming too much alcohol. This happens when the inebriated person passes out, and then vomits due to the effects of alcohol on the stomach. If someone's unconscious, it's possible to aspirate the liquid contents and possibly solid food from the stomach into the lungs, causing aspiration pneumonia.