Pneumonia is caused by several different microorganisms, most commonly bacteria and viruses. Viral pneumonia is more diffuse and is commonly caused by influenza virus, adenovirus and, in young children, respiratory syncytial virus (RSV). Bacterial agents are most commonly Streptococcus pneumoniae and Klebsiella pneumoniae. Bronchopneumonia (bronchial pneumonia) begins in terminal bronchioles, which become clogged with exudate and form consolidated (solidified) patches. Lobar pneumonia is an acute disease that involves one or more lobes of the lung. Pneumonia usually can be treated successfully in otherwise healthy people, but in debilitated patients it is a leading cause of death. Immunocompromised patients, such as those with AIDS, are often subject to a form of pneumonia called Pneumocystis carinii pneumonia (PCP), which is caused by a protozoon.
The term pneumonia is also applied to inflammation of the lungs caused by noninfectious causes, such as asthma, allergy, or inhalation of irritants. In these cases, however, the more general term pneumonitis is often used.
The incidence of tuberculosis (TB) has increased in recent years, along with the increase of AIDS and the appearance of antibiotic resistance in the organism that causes the disease, Mycobacterium tuberculosis (MTB). (This organism, because of its staining properties, also is referred to as AFB, meaning acid-fast bacillus.) The name tuberculosis comes from the small lesions, or tubercles, that appear with the infection. The symptoms of TB include fever, weight loss, weakness, cough and, as a result of damage to blood vessels in the lungs, hemoptysis, the coughing up of sputum containing blood. Sputum analysis is used to isolate, stain, and identify infectious organisms. Accumulation of exudate in the alveoli may result in consolidation of lung tissue. The tuberculin test is used to test for tuberculosis infection. The test material that is used, tuberculin, is made from byproducts of the tuberculosis organism. PPD (purified protein derivative) is the form of tuberculin commonly used.
Influenza is a viral disease of the respiratory tract. Different strains of the influenza virus have caused serious epidemics throughout history.
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