mōn`yə), acute infection of one or both lungs that can be caused by a bacterium, usually Streptococcus pneumoniae (also called pneumococcus; see streptococcus streptococcus (strĕp'təkŏk`əs), any of a group of gram-positive bacteria, genus Streptococcus,..... Click the link for more information. ), or by a virus, fungus, or other organism. The causal organisms reach the lungs through the respiratory passages. Usually an upper respiratory infection precedes the disease. Alcoholism, extreme youth or age, debility, immunosuppressive disorders and therapy, and compromised consciousness are predisposing factors. When one or more entire lobes of the lung are involved, the infection is considered a lobar pneumonia. When the disease is confined to the air spaces adjacent to the bronchi, it is known as bronchopneumonia. Aspiration pneumonia is the pathological consequence of the abnormal entry of fluids, particulate matter, or secretions in the lower airways.
The symptoms of pneumonia are high fever, chills, pain in the chest, difficulty in breathing, cough, and sputum that is pinkish at first and becomes rust-colored as the infection progresses. The skin may turn bluish because the lungs are not sufficiently oxygenating the blood. Complete bed rest and good supportive care are important. Oxygen helps to relieve severe respiratory difficulty.
Immunization for pneumococcal pneumonia is recommended for children under two years old, adults 65 or older, and others at risk. Penicillin is most commonly used to treat pneumococcal pneumonia and other pneumonias caused by bacteria and, with the other antibiotic and sulfa drugs, is responsible for the marked decline since the mid-20th cent. in mortality figures. Nevertheless, pneumonia is still a serious disease, especially in elderly and debilitated persons (who usually acquire bronchopneumonia) or when complicated by bacterial invasion of the bloodstream, membranes of the heart, or the central nervous system.
Viral pneumonia, generally milder than the bacterial form, is the result of lower respiratory infection and has been the cause of more than 90% of deaths for individuals over 65. Pneumocystis carinii pneumonia, which is caused by an organism traditionally thought to be a parasitic protozoan but now suspected to be a fungus, generally only occurs in patients who have AIDS or leukemia or whose immune system is otherwise suppressed.
pneumonia
Inflammation and solidification of lung tissue caused by infection, foreign particle inhalation, or irradiation but usually by bacteria. Mycoplasma pneumoniae is the most common cause in healthy individuals. The bronchi and alveoli may be inflamed. Coughing becomes severe and may bring up flecks of blood. It can be serious but is rarely fatal. Streptococcus pneumoniae is more common and generally more severe but usually affects only those with low resistance, especially in hospitals. A highly lethal form caused by Klebsiella pneumoniae is almost always confined to hospitalized patients with low immunity. Other bacterial pneumonias include Pneumocystis carinii pneumonia (rare except in AIDS) and Legionnaire disease. Most respond to antibiotic treatment. Viruses set the stage for bacterial pneumonia by weakening the individual's immune system more often than they cause pneumonia directly. Fungal pneumonia usually occurs in hospitalized persons with low resistance, but contaminated dusts can cause it in healthy individuals. It can develop rapidly and may be fatal. X-ray treatment (see radiation therapy) of structures in the chest may cause temporary lung inflammation.
pneumonia
Pneumonia
An acute or chronic inflammatory disease of the lungs. More specifically when inflammation is caused by an infectious agent, the condition is called pneumonia; when the inflammatory process in the lung is not related to an infectious organism, it is called pneumonitis.
An estimated 45 million cases of infectious pneumonia occur annually in the United States, with up to 50,000 deaths directly attributable to it. Pneumonia is a common immediate cause of death in persons with a variety of underlying diseases. With the use of immunosuppressive and chemotherapeutic agents for treating transplant and cancer patients, pneumonia caused by infectious agents that usually do not cause infections in healthy persons (that is, pneumonia as an opportunistic infection) has become commonplace. Moreover, individuals with acquired immune deficiency syndrome (AIDS) usually die from an opportunistic infection, such as pneumocystis pneumonia or cytomegalovirus pneumonia. Concurrent with the variable and expanding etiology of pneumonia and the more frequent occurrence of opportunistic infections is the development of new antibiotics and other drugs used in the treatment of pneumonia. See Acquired immune deficiency syndrome (AIDS), Opportunistic infections
Bacteria, as a group, are the most common cause of infectious pneumonia, although influenza virus has replaced Streptococcus pneumoniae (Diplococcus pneumoniae) as the most common single agent. Some of the bacteria are normal inhabitants of the body and proliferate to cause disease only under certain conditions. Other bacteria are contaminants of food or water.
Most bacteria cause one of two main morphologic forms of inflammation in the lung. Streptococcus pneumoniae causes lobar pneumonia, in which an entire lobe of a lung or a large portion of a lobe becomes consolidated (firm, dense) and nonfunctional secondary to an influx of fluid and acute inflammatory cells that represent a reaction to the bacteria. This type of pneumonia is uncommon today, usually occurring in people who have poor hygiene and are debilitated. If lobar pneumonia is treated adequately, the inflammatory process may entirely disappear, although in some instances it undergoes a process called organization, in which the inflammatory tissue changes into fibrous tissue, usually rendering that portion of the lung nonfunctional.
The other morphologic form of pneumonia, which is caused by the majority of bacteria, is called bronchopneumonia. In this form there is patchy consolidation of lung tissue, usually around the small bronchi and bronchioles, again most frequently in the lower lobes. This type of pneumonia may also undergo complete resolution if there is adequate treatment, although rarely it organizes.
Viral pneumonia is usually a diffuse process throughout the lung and produces a different type of inflammatory reaction than is seen in bronchopneumonia or lobar pneumonia. Mycoplasma pneumonia, caused by Mycoplasma pneumoniae, is referred to as primary atypical pneumonia and causes an inflammatory reaction similar to that of viral pneumonia.
Pneumonia can be caused by a variety of other fungal organisms, especially in debilitated persons such as those with cancer or AIDS. Mycobacterium tuberculosis, the causative agent of pulmonary tuberculosis, produces an inflammatory reaction similar to fungal organisms. See Mycobacterial diseases, Tuberculosis
Legionella pneumonia, initially called Legionnaire's disease, is caused by bacteria of the genus Legionella. The condition is frequently referred to under the broader name of legionellosis. See Legionnaires' disease
The signs and symptoms of pneumonia and pneumonitis are usually nonspecific, consisting of fever, chills, shortness of breath, and chest pain. Fever and chills are more frequently associated with infectious pneumonias but may also be seen in pneumonitis. The physical examination of a person with pneumonia or pneumonitis may reveal abnormal lung sounds indicative of regions of consolidation of lung tissue. A chest x-ray also shows the consolidation, which appears as an area of increased opacity (white area). Cultures of sputum or bronchial secretions may identify an infectious organism capable of causing the pneumonia.
The treatment of pneumonia and pneumonitis depends on the cause. Bacterial pneumonias are treated with antimicrobial agents. If the organisms can be cultured, the sensitivity of the organism to a specific antibiotic can be determined. Viral pneumonia is difficult to treat, as most drugs only help control the symptoms. The treatment of pneumonitis depends on identifying its cause; many cases are treated with cortisone-type medicines.
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