Pneumonia << noo MOHN yuh >> is a general term for lung diseases involving inflammation. Most cases of pneumonia result from infection. Most cases are caused by viruses or bacteria. But some result from fungi or other microbes. A few cases are caused by allergic reactions or by inhaling irritating chemicals.
Before the development of antibiotic drugs during the 1940’s, pneumonia killed about a third of its victims. Today, most pneumonia patients recover. But pneumonia still ranks as one of the leading causes of death in the United States. About 50,000 Americans die of the disease each year.
People with other serious health problems have the greatest risk of getting pneumonia. They also have the most difficulty recovering from it. These individuals include people with other diseases, such as diabetes, cancer, or kidney disease. Heavy smokers and alcoholics are also at risk. So are people with conditions that weaken the body’s resistance to infection. Pneumonia is one of the illnesses most commonly associated with AIDS (acquired immunodeficiency syndrome), a disease that weakens the body’s immune system. Children and elderly people also have a greater than average risk of developing pneumonia.
How pneumonia develops.
In some cases, a person gets pneumonia by inhaling small droplets that contain viruses or bacteria. These droplets are sprayed into the air when an infected person coughs or sneezes. In most other cases, pneumonia results when bacteria normally present in the nose, mouth, or throat invade the lungs. The body’s defense mechanisms ordinarily prevent these bacteria from reaching the lungs. But if the body’s defense mechanisms are weakened or are already fighting other diseases, pneumonia may develop. Such an infection is called opportunistic. Patients hospitalized for other diseases may develop pneumonia from opportunistic microbes or exposure to infectious agents from other patients.
In the lungs, the microbes that cause pneumonia can lodge in the air sacs. In the air sacs, oxygen is normally exchanged for carbon dioxide in the blood. There, the microbes can multiply rapidly. The air sacs may fill with fluid and with white blood cells produced by the body to fight the infection. When a lobe (major section) of a lung is affected, the infection is called lobar pneumonia. The infection is called bronchial pneumonia if it primarily affects the bronchioles (tiny air passages of a lung). Interstitial pneumonia chiefly affects the interstitium, the small spaces between the air sacs and the blood vessels.
Many kinds of viruses can cause pneumonia. These viruses include the ones that cause influenza and other respiratory infections. The most common bacterial causes of pneumonia include Streptococcus pneumoniae, also called pneumococci; Staphylococcus aureus; and Haemophilus influenzae. Mycoplasma pneumoniae is a bacterialike organism that frequently causes pneumonia in children and young adults. Pneumonia associated with Legionnaires’ disease is caused by the bacteria Legionella pneumophila or Legionella micdadei. A microbe called Pneumocystis carinii causes pneumonia in patients with weakened immune systems, such as people with AIDS.
Symptoms and diagnosis.
The symptoms of pneumonia vary with the type of microbe involved and the patient’s general health before the onset of the disease. In general, the symptoms of bacterial pneumonia are more severe than those of viral pneumonia. Most cases of bacterial pneumonia start with a sudden attack of chills, high fever, and chest pain. The patient also may develop a painful cough. The cough is dry at first but later produces rust-colored sputum (mucus and other substances from the lungs). Most cases of viral pneumonia are mild. Symptoms include fever, weakness, cough, and production of sputum.
Using a stethoscope, a physician can hear characteristic sounds from the lungs that indicate the presence of pneumonia. X rays and laboratory tests confirm the diagnosis. To determine the type of bacteria involved, the doctor examines the patient’s sputum under a microscope. Sputum samples are treated with chemicals and stains to make the infecting bacteria visible with a microscope. Other sputum samples are used to culture (grow) the infecting organisms in laboratory dishes or test tubes. Culturing the sample helps determine its identity. Antibody tests can identify many viruses that cause pneumonia.
Treatment and prevention.
Many people with pneumonia require complete bed rest in a hospital. Hospitalization may not be necessary in mild cases. For viral pneumonia, there is no other specific treatment. Some severe cases may require antiviral drugs. The majority of cases of viral pneumonia clear up within a few days or weeks. Physicians use antibiotics to treat bacterial pneumonia. They select the antibiotic thought to be the most effective in killing the specific kind of bacteria involved. Some pneumococci and other bacteria have become resistant to antibiotics, complicating treatment.
Influenza vaccinations protect against pneumonia caused by influenza viruses. Another vaccine protects the body from pneumonia caused by pneumococci. But doctors recommend it only for elderly people, patients with a long-term illness, and other people with a high risk of catching pneumonia.
