Encyclopedia / P / Pneumonia


What Is Pneumonia?

Pneumonia is a type of pneumonitis—an inflammation of the lungs that may be caused by the inhalation of irritating gases or particles or by an infection. When the inflammation is caused by an infectious microorganism, the term pneumonia is used.

The lungs have a complex system of defense: frequent branching and narrowing of the bronchial passages make it difficult for invaders to penetrate the lungs deeply; millions of tiny hairs, or cilia, in the bronchial lining constantly sweep particles out of the airways; the cough reflex forces irritating substances out of the lungs at high speed; and white blood cells, known as macrophages or scavenger cells, engulf and destroy many infectious agents.

Pneumonia is common, and can be a complication from a lingering cold or bout with influenza or bronchitis. Nearly half of community-acquired pneumonia cases are believed to be viral, about 30 percent are bacterial, and roughly 20 percent are thought to be caused by mycoplasmas, which are organisms that have both viral and bacterial characteristics. Pneumococcal pneumonia, the most common form of bacterial pneumonia in adults over 30, is caused by Streptococcus pneumoniae. This bacterium is found in the throats of many healthy people. When body defenses are weakened—by illness, old age, or impaired immunity, for example—the bacteria can work their way into the lungs and multiply.

Both bacterial and viral pneumonia can strike year-round, but the autumn and winter months, when colds and influenza proliferate, are major times for the disease, in part because people spend more time indoors, where bacteria and viruses can spread rapidly from one person to another. Our immunity may also be weakened somewhat by exposure to cold, allowing infectious organisms to take hold.

During pneumonia, inflammation may be limited to the air sacs called alveoli of the lung, a condition known as lobar pneumonia, or it may occur in patches throughout the lungs, originating in the airways and spreading to the alveoli (bronchopneumonia). An accumulation of fluid in the alveoli may impair transfer of oxygen to the bloodstream. The body’s cells may thus become starved of oxygen, and in severe cases respiratory failure may result. Until the development of antibiotics, pneumonia was the number one cause of death in the United States, and recently, strains of the most common cause of bacterial pneumonia (Streptococcus pneumoniae) have emerged that are penicillin resistant. Nevertheless, despite the serious health risks posed by the disease, the outlook for complete recovery is good, especially with early diagnosis and treatment.

Who Gets Pneumonia?

More than one million people are hospitalized annually with pneumonia, and about 50,000 people die from the disease. Of these, about one-third of cases occur in people over age 65. Approximately 4 out of every 100 children in the United States develop pneumonia each year. Bacterial pneumonia is very common, leading to an estimated 900,000 cases of pneumococcal pneumonia being diagnosed in the United States each year and accounting for most pneumonia-related deaths. Pneumonia, especially among the elderly or those already weakened by underlying illness, remains among the 10 leading causes of death today.

Those at the greatest risk for contracting pneumonia include adults age 65 and older, children younger than five years of age, people with underlying chronic medical conditions such as diabetes, those who have compromised immunity, those who smoke or are exposed to smoke, and people who have asthma. People who live in areas with high levels of air pollution, farm workers exposed to agricultural chemicals, construction or factory workers in industrial setting, and people who are frequently near many animals also have an increased risk of pneumonia.


Symptoms vary greatly depending on the type of pneumonia involved. The elderly and people with impaired immunity tend to have less pronounced symptoms and less fever, even though pneumonia is more dangerous among these patients.

  • Fever, usually over 100°F, possibly as high as 105°F, and chills.
  • Cough, possibly with bloody yellow or green sputum. A cough may persist for six to eight weeks after the infection, especially a viral infection, subsides.
  • Chest pain upon inhalation.
  • Shortness of breath.
  • Headache, sore throat, and muscle pain.
  • Weakness and fatigue.
  • Profuse perspiration.
  • Loss of appetite.
  • In severe cases: breathing difficulty, blue tinge to the skin, mental confusion.

Causes/Risk Factors

There are many different types of pneumonia. Most are caused by either a bacterial or viral infection.

  • Bacterial pneumonia is usually transmitted from person to person through coughing or sneezing. However, Legionnaires diseaseis a type of bacterial pneumonia that is transmitted by breathing in water vapor contaminated with Legionella bacteria. This strain of bacteria is sometimes found in the plumbing and air conditioning systems of large buildings or in poorly maintained hot tubs. This type of pneumonia does not spread from person to person.
  • Mycoplasma, a group of bacteria, is another type of organism that can cause pneumonia. Because it is highly contagious, this type usually occurs in older children and young adults in school or other group settings.
  • Viruses, such as the influenza virus and the common cold virus, are the most common cause of pneumonia in young children and the elderly. Measles and chickenpox(which is caused by the varicella-zoster virus), can be complicated by pneumonia.
  • Fungus or parasites can infect the lungs and cause fungal or parasitic pneumonia. These conditions are more common among patients with HIV/AIDS.
  • Inhaling dust, contaminated liquids, gases, or even food can also lead to pneumonia. Patients who require assisted breathing and are put on a ventilator can accidentally aspirate food or infected secretions from their mouth into the lungs. This kind of inhalation also occurs in people who pass out from drinking excessive amounts of alcohol and in patients whose gag reflex is impaired such as due to a brain injury. Vomit inhaled into the lungs, which may occur when a person loses consciousness, may cause what is known as aspiration pneumonia.
  • People with weakened immune systems, such as patients who have HIV or other chronic health conditions, and patients who have received an organ transplant, are at increased risk for pneumonia. Patients with these conditions can develop pneumonia from viruses that usually do not affect healthy people. Diabetes, chronic kidney disease, cancer, emphysema, heart disease, HIV/AIDS, and Sickle-cell disease pose a particular threat.
  • Other patients who are at increased risk include those struggling with alcoholism, patients who were recently hospitalized, those taking immunosuppressant drugs, post-operative patients with an impaired ability to cough or clear the lungs, patients in intensive care unitswho are on breathing tubes, patients who have their spleen removed, and patients who are undergoing chemotherapy.

What If You Do Nothing?

Most cases of viral pneumonia are relatively mild and clear up within one to two weeks. In fact, if the infection develops slowly, you may be unaware that you have pneumonia—a condition known as walking pneumonia. Bacterial pneumonia, on the other hand, is more serious. Left untreated, it can lead to scarring of lung tissue or the infection can spread to other vital organs. The earlier a diagnosis is made and treatment started, the less damage will be done to the lungs. Recovery may take anywhere from 10 days to three weeks. Anyone who develops a very high fever or experiences shortness of breath requires medical attention regardless of their current health status.


  • Patient history and physical examination.
  • Chest x-rays.
  • Blood and sputum cultures.
  • A biopsy of lung tissue may be performed in complicated cases.


  • Antibiotics are prescribed to treat a bacterial infection and should be taken for the full term prescribed. Stopping the medication too soon may produce a relapse.
  • Antifungal drugs, such as fluconazole or voriconazole, are prescribed to treat fungal pneumonia.
  • Antiviral drugs such as neuraminidase inhibitors, ribavirin, acyclovir, and ganciclovir sodium may be effective against some types of viral infection.
  • Analgesics reduce fever and pain. Rest in bed until fever subsides.
  • Over-the-counter cough suppressants containing dextromethorphan can help if you have a persistent dry cough. However, if you are coughing up sputum, suppressing the cough completely may encourage mucus accumulation in the lungs, potentially leading to serious complications.
  • Change body positions to drain mucus. Your doctor may instruct you how to drain mucus from your lungs by assuming various positions that lower your head below your torso, a technique known as postural drainage.
  • Drink plenty of fluids to stay hydrated. Patients who don’t have heart or kidney failure should drink at least eight glasses of water a day to loosen lung secretions and make them easier to expel.
  • Hospitalization may be recommended, especially during the early stages of infection and/or for patients who are elderly, since pneumonia may unexpectedly become severe within hours.
  • Oxygen may be administered through a mask to aid breathing. In severe cases a respirator may be required.
  • Excess fluid in the space surrounding the lungs may be removed by aspiration with a syringe and needle inserted through the chest wall.


Fortunately, a vaccine is available to help prevent pneumococcal pneumonia. Unlike flu shots, which must be given each year to cope with the newest strains of virus, a single pneumonia vaccination confers immunity for many years. There are now two vaccines recommended for adults, including one that provides some long-term protection against 23 different strains of S. pneumoniae, which account for 90 percent of cases of pneumococcal pneumonia. The schedule for vaccination varies depending on a number of factors such as your age, health, and the type of vaccine you are receiving. The U.S. Centers for Disease Control and Prevention also recommends that a recently approved children’s vaccine be administered to all children under the age of 5. The number of doses and the time between doses will depend on a child’s age.

  • People at high risk for pneumonia should be immunized against pneumococcal pneumonia. These people include those over age 65; those with heart,

lung, or kidney disease, diabetes mellitus, or weakened immune systems; and alcoholics.              The vaccine is required only once; it provides long-term protection and is between 60 to          80% effective in those whose immune system is functioning normally.

  • Get a flu shot. An annual flu vaccination, particularly for people over age 65 is recommended because pneumonia is a common complication of severe influenza.
  • Don't smoke.

When To Call A Doctor

Call a doctor if you develop symptoms of pneumonia, especially a fever above 100°F, shortness of breath even when lying down, or bloody sputum from coughing. Call an ambulance if you experience difficulty in breathing or if a blue tinge to the lips, nose, or fingernails appears.

Reviewed by Allen J. Blaivas, D.O., Division of Pulmonary, Critical Care, and Sleep Medicine, VA New Jersey Health Care System, Clinical Assistant Professor, Rutgers New Jersey Medical School, East Orange, NJ. Review provided by VeriMed Healthcare Network.