Pneumonia

Pneumonia is infection of the small air sacs of the lungs (alveoli) and surrounding tissues.

The infection causes inflammation and deterioration of lung function. The lungs become unable to easily transfer oxygen to the blood, increasing the work of breathing.

Pneumonia occurs in people of all ages. However, it occurs far more commonly in older people, in whom it tends to be far more serious. Younger people with pneumonia can often be treated at home, whereas most older people with pneumonia must be hospitalized because the infection tends to worsen quickly.

Pneumonia often affects only a portion of a single lung but can affect an entire lung or even both lungs. In many older people, the lung infection spreads beyond the lungs. The infection can enter the blood (sepsis).

When pneumonia occurs among people living in houses or apartments within a community, it is called community-acquired pneumonia. However, pneumonia is even more likely among older people who are hospitalized (hospital-acquired pneumonia) or living in institutional settings, such as nursing homes (nursing home-acquired pneumonia). Older people in hospitals or institutions often have weakened defenses against infection. Further, infections spread more efficiently in a closed environment.

Causes

Bacteria are the most common microorganisms that cause pneumonia. However, viruses and fungi cause pneumonia as well. These microorganisms are everywhere and are inhaled into the lungs all the time. Yet pneumonia does not occur every time these microorganisms are inhaled. Pneumonia develops only when these microorganisms gain a foothold in the tiny air sacs of the lungs.

Normally, several defense mechanisms help prevent microorganisms from reaching the air sacs. Specialized cells lining the airways have microscopic hairlike projections that constantly sweep anything that does not belong in the lungs up and out. Coughing is another way the lungs rid themselves of microorganisms. If microorganisms do reach the air sacs, the immune system, which normally helps defend the body against infection, is usually able to destroy the microorganisms before pneumonia develops.

Certain characteristics and conditions make older people more likely to develop pneumonia. First, the system of cleansing the airways is not as effective as in younger people. Weakness may make coughing less vigorous. And, with aging, the immune system is weakened.

Among all older people, those at greater risk of developing pneumonia include the following:

• Those whose lungs have been damaged by smoking or chronic obstructive pulmonary disease (smoking irritates the lining of the lungs and paralyzes the cells that normally sweep and cleanse the airways)
• Those whose lungs have recently been irritated by a mild infection, such as a cold or, especially, influenza
• Those who have poor cough reflex or who are too weak (or who are in pain from recent surgery or an accident) to cough vigorously
• Those who are less able to fight off infections, such as those who are undernourished
• Those who are taking certain drugs, such as corticosteroids
• Those who have certain diseases, such as heart failure or diabetes
• Those who have cancer in or near the airways of the lungs (the cancer may block the airways and trap any microorganisms that have reached the air sacs)
• Those who are paralyzed (for example, by a spinal injury or stroke)
• Those who are unconscious (in part because they are unable to cough)

Microorganisms that produce pneumonia can end up in air sacs in several ways. In some cases, people inhale microorganisms (which are present in tiny droplets) when they are near someone already infected. Spread in hospitals and nursing homes often occurs this way. More common among older people, however, is the presence of bacteria in their throat (colonization). These bacteria may remain there harmlessly or suddenly cause pneumonia if mucus or food is inhaled into the airway (aspiration) instead of passed into the esophagus. When aspiration occurs, the food or mucus can make its way into the lungs, carrying the bacteria from the throat along for the ride. Rarely, microorganisms from elsewhere in the body reach the lungs by traveling through the bloodstream.

Streptococcus pneumoniae (pneumococcus) is the most common bacterial cause of community-acquired pneumonia. Other common bacterial causes include anaerobic bacteria (which grow in the absence of oxygen), Haemophilus influenzae, and Legionella pneumophila (which causes a type of infection called Legionnaires' disease). Influenza virus and respiratory syncytial virus can also cause community-acquired pneumonia in older people, as can Mycobacterium tuberculosis, the microorganism causing tuberculosis. Although fungi can cause community-acquired pneumonia, they more commonly cause pneumonia in hospitalized patients who may be sick or debilitated (for example, cancer patients receiving chemotherapy).

Staphylococcus aureus, Klebsiella, Proteus, Escherichia coli, and Pseudomonas aeruginosa are bacteria that often cause pneumonia that develops in hospitalized or institutionalized people, such as those in nursing homes. Outbreaks of influenza and respiratory syncytial virus infection are also common in nursing homes. Tuberculosis occurs in this setting as well.

Symptoms and Diagnosis

The most common symptom is a cough that produces mucus (sputum). Many minor viral infections cause cough; the difference is that pneumonia causes thick sputum that is usually yellow or green. It may be tinged with blood or have a rusty color.

Fever is common, and chills, chest pain, and shortness of breath may develop. Symptoms vary depending on how extensive the pneumonia is and on which microorganism is causing the infection.

A doctor checks for pneumonia by listening to the person's chest with a stethoscope. Pneumonia usually produces distinctively abnormal sounds in the lungs. These sounds are caused by narrowing of the airways or filling of the air sacs of the lung with inflammatory cells and fluid.

In most cases, the diagnosis is confirmed with a chest x-ray. Doctors usually obtain a sample of blood. They may try to obtain a sample of mucus that has been coughed up. The laboratory tries to make a preliminary identification of the microorganism (smear or stain) and to grow (culture) the microorganisms present in the samples. Knowing the exact type of microorganism usually helps doctors choose better treatment options. However, despite these tests, the precise microorganism cannot be identified in up to half of the people who have pneumonia. When the person is severely ill and is not helped by initial therapy, doctors can try to obtain better samples, often by inserting a long flexible tube (bronchoscope) into the airways.

Prevention

Pneumonia caused by the pneumococcus bacterium or by the influenza virus can often be prevented with a vaccine. The pneumococcal vaccine is given once to people 65 or older. Even if the vaccine does not prevent pneumococcal pneumonia, it usually lessens the infection's severity. People at high risk of becoming infected with this type of bacteria (for example, patients with chronic obstructive pulmonary disease or heart failure) may need the pneumococcus vaccine every 6 years.

Older people who are at risk of pneumonia from aspiration due to difficulty chewing and swallowing because of conditions such as a stroke need to take special precautions. They may be given food that is finely chopped or in the form of soft solids or thickened liquids. They should be as upright or erect as possible while eating and should remain upright for at least an hour after eating.

For those who cannot cough vigorously, exercises that encourage breathing deeply and therapy to clear mucus may help. These exercises often use a small inspirometer that requires deep breathing to raise a ball in a tube. These exercises are particularly important for those who have had chest or abdominal surgery or who smoke.

Quitting smoking is an essential part of prevention in smokers.

Treatment

The vast majority of older people with pneumonia are hospitalized, where they can be treated with intravenous antibiotics. Older people can get very sick very fast from pneumonia and tend to respond less well to oral antibiotics.

Treatment of pneumonia depends first on whether the cause is bacteria, a virus, or fungus. The mainstay of treating bacterial pneumonia is antibiotics. Most viral pneumonia gets better without specific treatment. Pneumonia caused by unusual microorganisms, such as tuberculosis, also requires drugs that kill the organisms.

Doctors usually give antibiotics immediately whenever they suspect bacterial pneumonia, even before the bacteria are identified. Prompt treatment with antibiotics helps reduce the severity of pneumonia and the chance of developing complications, some of which are fatal.

When choosing an antibiotic, doctors try to predict which type of bacteria is likely to be the cause. The doctor often changes the antibiotic later if the type of bacteria is identified and its susceptibility to various antibiotics becomes known.

People who are short of breath or whose blood is low in oxygen are given supplemental oxygen. Although rest is an important part of treatment, moving often and getting out of bed and into a chair are encouraged.