Pneumonia

I

Introduction

Pneumonia, inflammation of one or both lungs. In people with pneumonia, air sacs in the lungs fill with fluid, preventing oxygen from reaching blood cells and nourishing the other cells of the body. Sometimes the inflammation occurs in scattered patches in the tissue around the ends of the bronchioles, the smallest air tubes in the lungs. This is known as bronchopneumonia. In other cases the inflammation is widespread and involves an entire lobe of the lung. This condition is called lobar pneumonia. In the United States about 5 million cases of pneumonia are reported each year.

II

Causes of Pneumonia

Pneumonia has more than 30 different causes. Most cases of pneumonia result from infection with microorganisms, primarily viruses, bacteria, mycoplasmas (small, free-living particles with characteristics of both bacteria and viruses), and fungi. Pneumonia may also result from certain kinds of allergic reactions, inhalation of fluids or some gases, and the inhalation of ingested foods.

A

Viral Pneumonia

About 50 percent of pneumonia cases are caused by viruses, particularly those viruses that cause upper respiratory infections, such as the viruses that cause influenza, adenoviruses, and rhinoviruses. Most cases of viral pneumonia are mild and resolve spontaneously without specific treatment.

One exception is severe acute respiratory syndrome (SARS), a type of viral pneumonia. SARS typically begins with a fever of 38.0°C (100.4°F) or more, chills, headache, and malaise. Two to seven days later some people develop a dry cough and difficulty breathing. For these people SARS can cause death.

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B

Bacterial Pneumonia

Infection with the Streptococcus pneumoniae bacterium, also called pneumococcus, is the most common cause of bacterial pneumonia. Pneumococcus usually causes lobar pneumonia, attacking an entire lobe or portion of a lobe of the lung; in double pneumonia, pneumococcus attacks both lungs. Pneumococcal lobar pneumonia often occurs in winter after an acute, viral upper respiratory infection. Usual symptoms include a shaking chill followed by a fever of about 40°C (104°F), pain in the chest while breathing, a cough, and blood-streaked sputum.

Other bacteria that cause pneumonia include Klebsiella pneumoniae, Haemophilus influenzae, Legionella pneumophilia (the bacterium that causes Legionnaires’ disease), and various staphylococci and streptococci bacteria. Infections with these organisms primarily cause bronchopneumonia. Onset of symptoms is generally slower than with lobar pneumonia, and the fever is lower.

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