Your lungs have built-in mechanisms for filtering out foreign substances that are inhaled with each breath. Despite these mechanisms, however, with repeated exposure to infectious agents such as viruses and bacteria, or with a change in your immune system, your risk of contracting a respiratory infection increases. This is especially true if your lungs have been damaged by smoking or exposure to environmental pollutants or if you have a chronic disease or take medications that decrease the effectiveness of your immune system. Some infectious microorganisms that enter the body through the lungs can affect many different organ systems. Others remain in the lungs, causing infection and inflammation.
Pneumonia
Pneumonia refers to an infection of the lungs. Lobar pneumonia is usually restricted to a single lobe of one lung (although more than one lobe may be involved), while bronchial pneumonia affects more widespread areas in both lungs. The specific type of pneumonia depends on the agent causing the infection. The three major microorganisms that cause pneumonia are viruses, bacteria, and mycoplasmas.
About half of all cases of pneumonia are caused by viruses. This type of pneumonia is most common in infants and children, older adults, and people whose immune systems are not working effectively. Viral pneumonia has symptoms similar to those of the flu: fever, headache, muscle pain, weakness, dry cough, and breathlessness. Medications are available to combat some of the viruses that can cause pneumonia, but antibiotics should not be prescribed, and would not be beneficial, unless bacteria are causing the infection.
Bacterial infection accounts for 30 to 50 percent of pneumonia cases in adults. Streptococcus pneumoniae (pneumococcus) is the most common bacterium involved, although many other microorganisms can cause bacterial pneumonia. The bacteria that cause pneumonia can spread throughout the body once they have entered the lungs. This can result in infection in the bloodstream (bacteremia or sepsis), the covering of the brain (meningitis), the lining of the heart (endocarditis), or the fluid in the joints (septic arthritis). Symptoms of pneumococcal pneumonia can appear either suddenly or gradually and include fever, pain on the affected side, shortness of breath, and a cough that produces mucus (the mucus is often blood-streaked).
Another type of bacterial pneumonia, called legionnaires’ disease, is caused by the Legionella pneumophila bacterium. The natural habitats for these bacteria are bodies of water, but they also thrive in the evaporative condensers of airconditioning systems and may be found in humidifiers and vaporizers as well. Legionnaires’ disease is most common among middle-aged men. Risk factors include smoking, alcohol abuse, and a suppressed immune system (especially due to taking corticosteroid medications). The fever associated with legionnaires’ disease is usually high, and other flulike symptoms occur, such as a vague sense of being ill, a cough, muscle pain, and a headache. The cough is initially dry but produces more mucus as the disease progresses. Antibiotics will eliminate the bacteria, but recovery may be slow.
Mycoplasmas are microorganisms that have characteristics of both bacteria and viruses. They tend to cause a mild but widespread form of pneumonia. Mycoplasma pneumonia is most common among children and young adults, especially those in closed communities such as schools, military barracks, and families. This microorganism acts by attaching to and destroying the cilia throughout the airways. Early symptoms (such as a vague sense of being ill, sore throat, and a dry cough) resemble the flu, but gradually, violent coughing bouts develop. Most people recover without treatment, although the use of certain antibiotics can speed recovery in some cases.
Pneumonia also can develop if bacteria, food, or other substances (including liquids or vomit) are inhaled (aspirated) directly into the lungs. This may occur when a person is choking or unconscious. The resultant infection is called aspiration pneumonia. Because aspiration pneumonia can cause severe damage to the lungs, it is treated in the hospital with intravenous antibiotics and supplemental oxygen. If food or other substances remain lodged in the lungs, the doctor may need to perform a bronchoscopy to remove them. If a toxic chemical has been inhaled, it is a medical emergency. Call 911 or your local emergency number, or take the person to the nearest hospital emergency department without delay.
Tuberculosis
Tuberculosis (TB) was a leading cause of death in the United States until the 1940s, when antibiotics were developed that could effectively kill the bacteria that cause the disease (Mycobacterium tuberculosis). However, since the early 1980s, strains of the bacteria that are resistant to available drugs have developed, and tuberculosis has again become a major public health problem.
Mycobacterium tuberculosis (or M tuberculosis) is easily spread by coughing, sneezing, laughing, or singing but generally does not cause disease without repeated exposure. However, you can be infected with tuberculosis without having the active disease. This type of infection produces no symptoms and is known as a latent infection. Infection, with or without the active disease, results in a positive TB (or tuberculin) skin test.
Although anyone can contract tuberculosis, certain groups of people are at higher risk. This includes homeless people, poor and medically underserved people, prisoners, nursing home residents, intravenous drug users, people with alcoholism, people with HIV infection, people with AIDS, and people with any disease that reduces the effectiveness of their immune system. People who are in regular contact with at-risk populations are also more likely to become infected. People from countries with high rates of tuberculosis may bring the infection with them when they emigrate.
Active tuberculosis disease may produce no signs or symptoms other than a vague feeling of being ill. Sometimes the infection causes a cough that persists for more than 2 weeks and may produce bloody mucus. Other symptoms may include chest pain, difficulty breathing, fever, night sweats, fatigue, loss of appetite, and weight loss.
Because a latent infection with tuberculosis produces no symptoms, a person may be infected for years without realizing it. The infection may be discovered only after the person is examined or treated for another disease or through a routine screening with the tuberculin skin test.
Active tuberculosis is diagnosed with a chest X ray and microscopic examination and cultures of sputum samples expelled from the lungs. The tuberculin skin test is used both to screen people at risk for active tuberculosis and to identify people with a latent infection.
Treatment depends on factors such as whether the TB is active or inactive, whether it has spread to other tissues, or whether the person has been treated for TB previously. Two or more antibiotics (such as isoniazid and rifampin) are given together daily for at least 6 to 9 months; some drug combinations can be given daily for the first month and then twice a week for an additional 8 months, although in some cases, treatment must continue for years. Warning: If the drug therapy is not strictly followed, the bacteria may mutate and become resistant to the drugs being used. If you do not take the drugs exactly as prescribed, you could have very serious problems.
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