"Pneumonia" encompasses many different diseases that involve infection or inflammation of the lungs. Pneumonia affects the lungs in two ways. Lobar pneumonia affects a lobe of the lungs, and bronchial pneumonia can affect patches throughout both lungs. Together, pneumonia and influenza will represent a cost to the U.S. economy in2004 of $37.5 billion, $5.6 billion due to indirect mortality costs and $31.9 billion in direct costs.

Pneumonia and influenza together are ranked as the seventh leading cause of death in the United States. Pneumonia consistently accounts for the overwhelming majority of deaths. In 2002, 64,954 people died of pneumonia.
In 1996 (latest data available), there were an estimated 4.8 million cases of pneumonia resulting in 54.6 million restricted-activity days and 31.5 million bed days. That same year, pneumonia along with other respiratory conditions, such as the common cold and acute bronchitis, substantially contributed to days lost from work (99.3 per 100 currently employed persons) and school (152.2 per 100 youths).

An estimated 618,000 hospital discharges in males (44.0 per 10,000) and 694,000 discharges in females (474.3 per 10,000) all attributable to pneumonia in 2002. The highest discharge rate that year was seen in those 65 and over at 218.8 per 10,000.

Pneumonia is mainly caused by viruses, bacteria and mycoplasmas. Pneumonia can also be caused by the inhalation of food, liquid, gases or dust, and by fungi. One type of pneumonia caused by fungi is pneumocystis carinii pneumonia (PCP) which primarily affects AIDS patients. Certain diseases, such as tuberculosis, can also cause pneumonia.

Approximately 50 percent of pneumonia cases are believed to be caused by viruses and tend to result in less severe illness than bacterial-caused pneumonia. Viral pneumonia is less common in normal adults with a fully functioning immune system; however, 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, fever and increasing breathlessness.

Streptococcus pneumoniae or pneumococcal pneumonia is the most common cause of bacterial pneumonia acquired outside of hospitals. The bacteria can multiply and cause serious damage to healthy individual lungs, bloodstream (bacteremia), brain (meningitis) and other parts of the body, especially when the body's defenses are weakened. Pneumococcal pneumonia accounts for 25 to 35 percent of all community-acquired pneumonia, and an estimated 40,000 deaths yearly.

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 lack of oxygen.
Mycoplasmas are the smallest free-living agents of disease in man, with characteristics of both bacteria and viruses. The agents generally cause a mild and widespread pneumonia. The most prominent symptom of mycoplasma pneumonia is a cough that tends to come in violent attacks, but produces only spare whitish mucus. Mycoplasmas are responsible for approximately 20 percent of all cases of pneumonia.

People considered at high risk for pneumonia include the elderly, the very young, and those with underlying health problems, such as chronic obstructive pulmonary disease (COPD), diabetes mellitus, congestive heart failure and sickle cell anemia. Patients with diseases that impair the immune system, such as AIDS, or those undergoing cancer therapy or organ transplantation, or patients with other chronic illnesses are particularly vulnerable.

There are no generally effective treatments for most types of viral pneumonia, which usually heal on their own. Early treatment with antibiotics can cure bacterial pneumonia and speed recovery from mycoplasma pneumonia. However, the disease has become more resistant to these drugs, making treatment of pneumococcal infections more difficult.

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