Pneumonia

Introduction

Every year, more than 60,000 Americans die of pneumonia, an inflammation of the lungs that's usually caused by infection with bacteria, viruses, fungi or other organisms. Pneumonia is a particular concern for older adults and people with chronic illnesses or impaired immune systems, but it can also strike young, healthy people. Worldwide, it's a leading cause of death in children.

There are many kinds of pneumonia ranging in seriousness from mild to life-threatening. Although signs and symptoms vary, many cases of pneumonia develop suddenly, with chest pain, fever, chills, cough and shortness of breath. Infection often follows a cold or the flu, but it can also be associated with other illnesses or occur on its own.

Although antibiotics can treat some of the most common forms of bacterial pneumonias, antibiotic-resistant strains are a growing problem. For that reason, and because the disease can be very serious, it's best to try to prevent infection in the first place.

Signs and symptoms

Pneumonia can be difficult to spot. It often mimics a cold or the flu, beginning with a cough and a fever. Chest pain is a common symptom of many types of pneumonia. Pneumonia symptoms can vary greatly, depending on underlying conditions and the type of organism causing the infection:

Bacteria - Many types of bacteria can cause pneumonia. Bacterial pneumonia can occur independently, at the same time as viral pneumonia, or may develop after having a viral upper respiratory infection such as influenza. Signs and symptoms include: shaking chills, a high fever, sweating, shortness of breath, chest pain, and a cough that produces thick, greenish or yellow phlegm. Bacterial pneumonia is often confined to just one area (lobe) of the lung. This is called lobar pneumonia.

Viruses - About half the reported cases of pneumonia are caused by viruses. Viral pneumonia tends to begin with flu-like signs and symptoms. It usually starts with a dry cough, headache, fever, muscle pain and fatigue. As the disease progresses, patients may become breathless and develop a cough that produces just small quantities of phlegm that may be clear or white. Patients with viral pneumonia run the risk of also developing a secondary bacterial pneumonia

Mycoplasma - This tiny organism causes signs and symptoms similar to those of other bacterial and viral infections, although symptoms appear more gradually and are often mild and flu-like. Patients are usually not sick enough to stay in bed or to seek medical care and may never even know they've had pneumonia. That's why this type of pneumonia is often called walking pneumonia. Mycoplasma pneumonia spreads easily in situations where people congregate and is common among schoolchildren and young adults.

Fungi - Certain types of fungus can cause pneumonia, although these types of pneumonia are much less common. Most people experience few if any symptoms after inhaling these fungi, but some develop symptoms of acute pneumonia, and still others may develop a chronic pneumonia that persists for months.

Pneumocystis carinii - Pneumonia caused by P. carinii is an opportunistic infection that affects people living with AIDS. People whose immune systems are compromised by organ transplants, chemotherapy, or treatment with corticosteroids or other immune-suppressing drugs such as tumor necrosis factor (TNF) inhibitors also are at risk. The signs and symptoms of Pneumocystis carinii pneumonia include a cough that doesn't go away, fever, and shortness of breath.

Causes

The lungs are two spongy organs surrounded by a moist membrane (the pleura). Each lung is divided into lobes, three on the right and two on the left. During inhalation, air is carried through the trachea to the lungs. The lungs contain major airways called bronchi. The bronchi repeatedly subdivide into many smaller airways (bronchioles), which finally end in clusters of tiny air sacs called alveoli.

The body has mechanisms to protect the lungs from infection. In fact, frequent exposure to bacteria and viruses that can cause pneumonia is normally prevented by the body's defense mechanism. For example, the nasal cilia screen out a lot of organisms but can't stop all from getting into the airways. Sometimes, these microorganisms get past the body's defenses, finding their way into the alveoli.

There, white blood cells (leukocytes) begin to attack the invading organisms. The accumulating pathogens, white cells and immune proteins cause the air sacs to become inflamed and filled with fluid, leading to the difficult breathing that characterizes many types of pneumonia. If both lungs are involved, it's called double pneumonia.

Classifications of pneumonia

Pneumonia is sometimes classified according to the cause of pneumonia:

Community-acquired pneumonia - This refers to pneumonia acquired from the external environment.

Hospital-acquired (nosocomial) pneumonia - Hospitals are a breeding ground for bacteria and viruses, placing patients at a higher risk of pneumonia.

Aspiration pneumonia - This type of pneumonia occurs when foreign matter is inhaled (aspirated) into the lungs, often from the digestive tract.

Pneumonia caused by opportunistic organisms - This type of pneumonia strikes people with compromised immune systems. Organisms that aren't harmful for healthy people can be extremely dangerous for people with AIDS, organ transplantation and other conditions that impair the immune system.

Emerging pathogens - Outbreaks of the H5N1 influenza (bird flu) virus and severe acute respiratory syndrome (SARS) have caused serious, sometimes deadly pneumonia infections, even in otherwise healthy people.

Risk factors

Adults age 65 or older and very young children, whose immune systems aren't fully developed, are at increased risk of pneumonia. Patients are also at risked if they:

Have certain diseases - These include immune deficiency diseases such as HIV/AIDS and chronic illnesses such as cardiovascular disease, emphysema and diabetes.

Smoke or abuse alcohol - Millions of microscopic hairs (cilia) cover the surface of the cells lining the bronchial tubes. These hairs clear the airways of normal secretions, but irritants such as tobacco smoke paralyze the cilia, causing secretions to accumulate. If these secretions contain bacteria, they can develop into pneumonia. Alcohol interferes with your normal gag reflex as well as with the action of the white blood cells.

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