The term “pneumonia” most commonly refers to an infection of the lungs that causes inflammation in the lung tissue, and fluid in or around the air sacs of the lungs Figure 01.
Pneumonia is the sixth most common cause of death in the United States. It can occur any time of the year, but is more common during the winter.
In most cases of pneumonia, a germ invades the lung tissue and causes it to become inflamed (swell). This may cause fluid to collect inside or around the air sacs of the lungs (alveoli). The fluid interferes with the ability of the lung to take in oxygen and move it to the cells of the body, where it is needed. The body is also stressed because it has to work to fight the infection that caused the pneumonia.
Doctors usually divide pnemonia into three types: community-acquired, nursing home-acquired, and hospital-acquired. Community-acquired pneumonia (CAP) is transmitted between people in the course of their normal activities. Nursing home-acquried pneumonia is spread between residents of a nursing home. Hospital-acquired pneumonia (also called nosocomial pneumonia) is spread between patients in the hospital. It is important for clinicians to find out where a person may have caught pneumonia, since different germs are more likely in each environment. This may help the clinician better treat the pneumonia.
People with pneumonia may have symptoms ranging from mild to severe, depending on their age, their general health, and the cause of their pneumonia.
Figure 01. How Pneumonia Happens
Infectious pneumonia occurs when microorganisms (germs) invade the lungs. Bacteria and viruses are the most common causes of pneumonia. These tiny organisms can reach the airways by being inhaled, or by moving there from other areas of the body Table 01.
There are more than 50 known organisms that can cause pneumonia. That is why the exact organism causing some cases of pneumonia can be difficult for clinicians to identify.
Organisms that cause pneumonia may be directly inhaled from the environment. They can also move into the lungs from the areas around the mouth and in the throat, where they normally thrive without causing any harm. Infections from other areas of the body can also move into the lungs and cause pneumonia.
Table 1. Some Common Pneumonias and Why They Happen
Type of pneumonia Why it happens Bacterial Pneumonia This type of pneumonia usually starts after the flu, a cold, or an upper respiratory infection (URI) has weakened the immune system. Weakened defenses allow bacteria to multiply in the lungs, causing illness. There are many different bacteria that can cause pneumonia. The most common is Streptococcus pneumoniae (pneumococcus). Germs may be spread when an infected person coughs or sneezes or touches objects with unwashed hands. Bacterial pneumonia can be more serious than viral pneumonia. Viral Pneumonia Many different viruses can cause viral pneumonia. Examples include influenza, chickenpox, herpes simplex, and respiratory syncytial virus (RSV). Viruses can be passed between humans through coughing or sneezing, or by touching something that has come in contact with fluid from an infected person. Fungal Pneumonia Different kinds of fungi can cause pneumonia. It is most often caused by fungi inhaled from the environment. Mycoplasmal Pneumonia Mycoplasmas are tiny organisms that are easily spread where many people congregate (such as schools or office buildings). This type of pneumonia is usually very mild, and may be referred to as ?walking pneumonia.? Pneumocystis Pneumonia The parasite pneumocystis carinii, which normally resides in the lungs without causing problems, may grow too much and cause pneumonia in people whose immune systems are weak as a result of AIDS, organ transplant, cancer, or chemotherapy. Aspiration Pneumonia Aspiration pneumonia occurs when stomach contents or a foreign object is inhaled into the air passages, causing injury, infection, or blockage. Legionnaires' Disease Caused by a bacterium that lives in water, Legionnaires' disease can be spread through contaminated plumbing, showerheads, or air conditioning.
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