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. Pneumonia acquired while in the hospital can be particularly virulent and deadly. 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.

You’re more likely to develop pneumonia if you:

Have certain diseases. These include immune deficiency diseases such as HIV/AIDS and chronic illnesses such as cardiovascular disease, emphysema and diabetes. You’re also at increased risk if you’ve had your spleen removed, or your immune system has been impaired by chemotherapy or long-term use of immunosuppressant drugs.
Smoke, or abuse alcohol. Millions of microscopic hairs (cilia) cover the surface of the cells lining your bronchial tubes. The hairs beat in a wave-like fashion to clear your 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 that fight infection.
Are hospitalized in an intensive care unit. Pneumonia acquired in the hospital tends to be more serious than other types of pneumonia. People who require mechanical ventilation are particularly at risk because the breathing tube (endotracheal tube) bypasses the normal defenses of the respiratory tract, prevents coughing, may allow the stomach’s contents to back up into the esophagus where they can be aspirated, and can harbor bacteria and other harmful organisms.
Are exposed to certain chemicals or pollutants. Your risk of developing some uncommon types of pneumonia may be increased if you work in agriculture, construction or around certain industrial chemicals or animals. Exposure to air pollution or toxic fumes can also contribute to lung inflammation, which makes it harder for the lungs to clear themselves.
Have had surgery or experienced a traumatic injury. People who’ve had surgery or who are immobilized from a traumatic injury have a higher risk of pneumonia because surgery or serious injuries may make coughing — which helps clear the lungs — more difficult and lying flat can allow mucous to collect in your lungs, providing a breeding ground for bacteria.

Pneumonia can be difficult to spot. It often mimics a cold or the flu, beginning with a cough and a fever, so you may not realize you have a more serious condition. Chest pain is a common symptom of many types of pneumonia. Pneumonia symptoms can vary greatly, depending on any underlying conditions you may have and the type of organism causing the infection:

Bacteria. Many types of bacteria can cause pneumonia. Bacterial pneumonia can occur on its own, at the same time as viral pneumonia, or you may develop it after you’ve had a viral upper respiratory infection such as influenza. Signs and symptoms, which are likely to come on suddenly, include shaking chills, a high fever, sweating, shortness of breath, chest pain, and a cough that produces thick, greenish or yellow phlegm.

Ironically, high-risk groups such as older adults and people with a chronic illness or compromised immune system may have fewer or milder symptoms than less vulnerable people do. And instead of the high fever that often characterizes pneumonia, older adults may even have a lower than normal temperature.

Bacterial pneumonia is often confined to just one area (lobe) of the lung. This is called lobar pneumonia.

Viruses. About half of pneumonias are caused by viruses. Viral pneumonia tends to begin with flu-like signs and symptoms. It usually starts with a dry (nonproductive) cough, headache, fever, muscle pain and fatigue. As the disease progresses, you may become breathless and develop a cough that produces just small quantities of phlegm that may be clear or white. When you have viral pneumonia, you 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. You may not be sick enough to stay in bed or to seek medical care and may never even know you’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. Mycoplasma pneumonia responds well to treatment with the appropriate antibiotics, although you may continue to have a dry, nagging cough and continue to feel weak during your convalescence.

Fungi. Certain types of fungus also 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.

Your 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. When you inhale, air is carried through the windpipe (trachea) to your lungs. Inside your lungs, there are major airways called bronchi. The bronchi repeatedly subdivide into many smaller airways (bronchioles), which finally end in clusters of tiny air sacs called alveoli.

Your body has mechanisms to protect your lungs from infection. In fact, you’re frequently exposed to bacteria and viruses that can cause pneumonia, but your body normally prevents most of these organisms from invading and overwhelming your airways. For example, the nasal cilia screen out a lot of organisms but can’t stop all from getting into your airways. Sometimes — for reasons that aren’t always well understood — these microorganisms can get past your body’s defenses, finally finding their way into your lungs’ air sacs.

There, white blood cells (leukocytes), a key part of your immune system, 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 you acquire in the course of your daily life — at school, work or the gym, for instance.

Hospital-acquired (nosocomial) pneumonia. If you’re hospitalized, you’re at a higher risk of pneumonia, especially if you are on a mechanical ventilator, are in the intensive care unit or have a compromised immune system. This type of pneumonia can be extremely serious, especially for older adults, young children and people with chronic obstructive pulmonary diseases (COPD) or HIV/AIDS.

A common predisposing factor for this type of pneumonia is gastroesophageal reflux. This occurs when some of the contents of your stomach back up into the upper esophagus. From there, the gastroesophageal contents can be aspirated into the trachea and then into your airways. Even very small amounts of gastroesophageal reflux can lead to pneumonia in people who are hospitalized.

Aspiration pneumonia. This type of pneumonia occurs when foreign matter is inhaled (aspirated) into your lungs — most often when the contents of your stomach enter your lungs after you vomit. This commonly happens when a brain injury or other condition affects your normal gag reflex.

Another common cause of aspiration pneumonia is consuming too much alcohol. This happens when the inebriated person passes out, and then vomits due to the effects of alcohol on the stomach. If someone’s unconscious, it’s possible to aspirate the liquid contents and possibly solid food from the stomach into the lungs, causing aspiration pneumonia.

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. For example, P. carinii pneumonia almost never occurs in otherwise healthy people. Medications that suppress your immune system, such as corticosteroids or chemotherapy also can put you at risk of opportunistic pneumonia.
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.

Your doctor may first suspect pneumonia based on your medical history and a physical exam. During the exam, your doctor will listen to your lungs with a stethoscope to check for abnormal bubbling or crackling sounds (rales) and for rumblings (rhonchi) that signal the presence of thick liquid. Both these sounds may indicate inflammation caused by infection.     You’re also likely to have chest X-rays to confirm the presence of pneumonia and to determine the extent and location of the infection. You may also have blood tests to check your white cell count, or to look for the presence of viruses, bacteria or other organisms. Sometimes your doctor may examine a sample of your phlegm or your blood to help identify the microorganism that’s causing your illness.

The extent of all this testing depends on how sick you are and your underlying risk factors, and whether or not you’re responding to therapy.

How serious pneumonia is for you depends on your overall health and the type and extent of pneumonia you have. If you’re young and healthy, your pneumonia can usually be treated successfully. But if you have heart failure or lung ailments, especially from smoking, or if you’re older, your pneumonia may be harder to cure. You’re also more likely to develop complications, some of which can be life-threatening.

  • Bacteria in the bloodstream. Pneumonia can turn deadly when inflammation from the disease fills the air sacs in your lungs and interferes with your ability to breathe. In some cases the infection may invade your bloodstream (bacteremia). It can then spread quickly to other organs. This is detected by doing cultures of your blood.
  • Fluid accumulation and infection around the lungs. Sometimes fluid accumulates between the thin, transparent membrane (pleura) covering your lungs and the membrane that lines the inner surface of your chest wall — a condition known as pleural effusion. Normally, the pleurae are silky smooth, allowing your lungs to slide easily along your chest wall when you breathe in and out. But when the pleurae around your lungs become inflamed (pleurisy) — often as a result of pneumonia — fluid can accumulate and may become infected (empyema). In that case, you may have a tube placed between your ribs to drain the fluid or, occasionally, a surgical procedure to clear out some of the infected material.
  • Lung abscess. A cavity containing pus (abscess) that forms within the area affected by pneumonia is another potential complication. Abscesses usually are treated with antibiotics, but in rare cases they may need to be removed surgically.

If you have emphysema or pneumonia in both lungs (double pneumonia), you may need a mechanical respirator to help you breathe.

Pneumonia treatments vary, depending on the severity of your symptoms and the type of pneumonia you have.

Bacterial. Doctors usually treat bacterial pneumonia with antibiotics. Although you may start to feel better shortly after beginning your medication, be sure to complete your entire course of antibiotics. Stopping medication too soon may cause your pneumonia to return. It also helps create strains of bacteria that are resistant to antibiotics — an increasingly serious problem in the United States.
Viral. Antibiotics aren’t effective against most viral forms of pneumonia. And although a few viral pneumonias may be treated with antiviral medications, the recommended treatment is generally the same as for the flu — rest and plenty of fluids.
Mycoplasma. Mycoplasma pneumonias are treated with antibiotics. Even so, recovery may not be immediate. In some cases fatigue may continue long after the infection itself has cleared. Many cases of mycoplasma pneumonia go undiagnosed and untreated. The signs and symptoms mimic those of a bad chest cold, so some people never seek medical attention.
Fungal. If your pneumonia is caused by a fungus, you’ll likely be treated with antifungal medication.

In addition to these treatments, your doctor may recommend over-the-counter medications to reduce fever, treat your aches and pains, and soothe the cough associated with pneumonia. You don’t want to suppress your cough completely, though, since coughing helps clear your lungs. If you must use a cough suppressant, use the lowest dose that helps you get some rest.  If you have severe pneumonia, you’ll be hospitalized and treated with intravenous antibiotics and put on oxygen. If you don’t need oxygen, you may recover as quickly at home with oral antibiotics as in the hospital, especially if you have access to qualified home health care. Sometimes you may spend three or four days in the hospital receiving intravenous antibiotics and then continue to recover at home with oral medication.

Your doctor will most likely schedule a follow-up X-ray and an office visit after your initial diagnosis and treatment. By that time your infection should have cleared, but it’s important for your doctor to see you, even if you’re feeling better. Follow-up appointments and X-rays are especially important in smokers. If you’re not feeling better, the follow-up visit is an opportunity for your doctor to schedule tests to determine more specifically what’s causing your symptoms.

If you have pneumonia, the following measures can help you recover more quickly and decrease your risk of complications:

Get plenty of rest. Even when you start to feel better, be careful not to overdo it.
Drink lots of fluids, especially water. Liquids keep you from becoming dehydrated and help loosen mucus in your lungs.
Take the entire course of any prescribed medications. Stopping medication too soon can cause your pneumonia to come back and contributes to the development of antibiotic-resistant bacteria.
Keep all of your follow-up appointments. Even though you feel better, your lungs may still be infected. It’s important to have your doctor monitor your progress.