Definition of Pneumonia

pneumoniaPneumonia is inflammation of the lungs, usually the result of an infection, that causes the alveolar sacs to fill with fluid or pus.

It is the most serious consequence of influenza, and in combination with influenza is the seventh leading cause of death in the United States.

Pneumonia may be lobar, affecting the entire lobe of the lung, or bronchial, affecting diffuse areas of lung. The more of the lung that is involved, the more serious the consequences.

People most vulnerable to infection resulting in pneumonia and complications from pneumonia are the very young, the very old, and those who have immunodeficiency disorders such as hiv/aids or other serious health conditions such as cancer. About two million people in the United States develop pneumonia each year, and about 60,000 die as a result of the infection or its complications.

Pathogens that can cause pneumonia include viruses, bacteria, and fungi. The pneumonias that result from these pathogens are contagious-that is, an infected person can pass them to others through sneezing and coughing. Sputum (mucus and debris from the respiratory tract) contains the infective agent.

Pneumonia also can develop after exposure to bacteria aspirated into the lungs (such as in a person who is weak and vomiting). Nosocomial pneumonias develop from pathogens common in environments such as hospitals and skilled nursing facilities and infect people who are already weak as a result of other health conditions (especially those who are immunocompromised).

Types of Pneumonia


A number of viruses can cause pneumonia, the most common of which are influenza A, influenza B, parainfluenza, respiratory syncytial virus, adenovirus, varicella-zoster virus, epstein-barr virus, and coxsackievirus. Cytomegalovirus (cmv) pneumonia can develop in people who are immunocompromisedantiviral medications are available for some of these viral infections and can shorten the course of the infection and lessen the severity of symptoms. Most otherwise healthy people recover fully from viral pneumonia. Bacterial pneumonia may develop secondarily to viral pneumonia.


Pneumonia in people over age 30 is more likely to result from bacterial infection than other causes. Staphylococcus aureus, Haemophilus influenzae type b (Hib), Chlamydia pneumoniae, and Streptococcus pneumoniae are the strains of bacteria most commonly responsible for bacterial pneumonia. S. pneumoniae causes the most common form of bacterial pneumonia, pneumococcal pneumonia, which often follows a viral infection of the upper respiratory tract.

Hib pneumonia, despite the bacterium’s name, has nothing to do with the influenza virus and affects primarily young children. Hib vaccination has nearly eliminated this type among children in the United States. S. aureus tends to be opportunistic and accounts for about 20 percent of nosocomial pneumonia. Antibiotic medications are necessary to treat bacterial pneumonia. Even with antibiotic therapy, however, bacterial pneumonia is a serious illness that can be deadly among the very young and the very old.


Mycoplasma are tiny organisms related to bacteria, commonly called atypical bacteria. The pneumonia they cause is typically mild though tends to linger. A common nickname for mycoplasmal pneumonia as “walking pneumonia” because its symptoms are enough to make people feel unwell though usually not enough to interrupt regular activities. Most people recover without treatment, though antibiotics usually speed recovery. Cough and headache may persist for several weeks.


Fungi may cause pneumonia in people who take antibiotics for an extended period of time, as antibiotics suppress the normal flora (normally present bacteria) that otherwise keep fungi in check. Fungal pneumonias are rare but when invasive in someone who is immunocompromised, they can be life-threatening.

Pneumocystic Carinii Pneumonia

Pneumocystis carinii is an opportunistic pneumonia that occurs nearly exclusively in people who are immunocompromised, including those who have hiv/aids, are receiving immunosuppressive therapy following organ transplantation, or are undergoing chemotherapy for cancer treatment. During the early days of the AIDS epidemic, P. carinii pneumonia was often the first indication that a person had hiv/aids. Doctors may prescribe prophylactic antifungal medications for people at risk for P. carinii pneumonia. Such prophylaxis has now made Pneumocystic pneumonia a relatively rare event in people whose HIV infection is wellmanaged.

Symptoms and Diagnostic Path

The symptoms vary somewhat with the type of pneumonia, though commonly include

  • Cough that produces greenish yellow sputum or hemoptysis (bloody sputum)
  • Fever (sometimes high)
  • Chills or sweating
  • Generalized discomfort and aches
  • Fatigue
  • Chest discomfort or PAIN, especially with inhalation
  • Dyspnea (shortness of breath) or tachypnea (rapid breathing)

Symptoms may develop gradually or come on suddenly. Though the pattern of the symptoms provides good clues as to the cause of the pneumonia, the doctor cannot determine whether the infection is viral or bacterial without sputum or blood tests. Viral pneumonia does not respond to antibiotic therapy, though a good number of people who have viral pneumonia develop secondary bacterial pneumonia that does require antibiotics. The diagnostic path typically includes chest X-ray, which shows the areas of infiltration (fluid or pus accumulation) within the lungs.

Other factors that help determine the kind of pneumonia include knowledge of local or regional outbreaks of viral or bacterial pneumonia, history of recent upper respiratory infection or influenza, and the presence of other health conditions such as hiv/aids. sputum culture may also help in the diagnosis although most viruses and atypical bacteria do not readily grow in culture.

Treatment Options and Outlook

Treatment depends on the cause of the infection and may include antibiotics for bacterial pneumonia, antiviral medications or management of symptoms for viral pneumonia, and antifungal medications for fungal pneumonia. Because secondary bacterial pneumonia can develop as a complication of other types of bacteria, symptoms that fail to improve within 10 days or that worsen require further medical evaluation. Most people who are otherwise healthy make full recovery from pneumonia, though may take six to eight weeks to feel back to normal.

Risk Factors and Preventive Measures

The very young, the very old, and those who have serious health conditions of any kind are at greatest risk for pneumonia. Health experts recommend annual influenza immunization and pneumococcal vaccination for people who have such risks. Diligent hand washing and conscientious cough and SNEEZE precautions help reduce the spread of infectious agents. Early diagnosis and appropriate treatment reduce the likelihood of complications.


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