Pneumonia is an infection of the lungs that is caused by bacteria, viruses, fungi, or parasites. It is characterized primarily by inflammation of the alveoli in the lungs or by alveoli that are filled with fluid (alveoli are microscopic sacs in the lungs that absorb oxygen).
At times a very serious condition, pneumonia can make a person very sick or even cause death. Although the disease can occur in young and healthy people, it is most dangerous for older adults, babies, and people with other diseases or impaired immune systems.
In the United States, more than 3 million people develop pneumonia each year, and about 17% of these receive treatment in a hospital. Most people with pneumonia recover, but about 5% will succumb to the condition.
Fast facts on pneumonia
Here are some key points about pneumonia. More detail and supporting information is in the main article.
- Pneumonia is an infection of the lungs that can cause mild to severe illness in people of all ages.
- It is the leading cause of death in children younger than 5 years of age worldwide.
- Approximately 50% of pneumonia cases are believed to be caused by viruses and tend to result in less severe illness than bacteria-caused pneumonia.
- Pneumonia infections can often be prevented with vaccines and can usually be treated with antibiotics, antiviral drugs (such as Tamiflu) or specific drug therapies.
- Around 59.7% of adults 65 years and over have ever received the pneumonia vaccination.
- Pneumonia and influenza together are ranked as the eighth leading cause of death in the US.
- It is estimated that 175,000 cases of pneumococcal pneumonia occur each year, with a fatality rate of 5-7%, or even much higher among the elderly.
- Around 53,282 people die per year in the US from pneumonia.
- People considered at high risk for pneumonia include the elderly (over 65 years of age), the very young and those with underlying health problems.
- The pneumococcal polysaccharide vaccine (PPSV) is recommended for anyone over 65 years of age and all those over 2 years of age who have asthma or long-term health problems.
What causes pneumonia?
Bacteria and viruses are the primary causes of pneumonia. When a person breathes pneumonia-causing germs into his lungs and his body's immune system cannot otherwise prevent entry, the organisms settle in small air sacs called alveoli and continue multiplying. As the body sends white blood cells to attack the infection, the sacs become filed with fluid and pus - causing pneumonia.
Pneumonia has bacterial, viral, fungal, and other primary causes. A summary is provided below.
Streptococcus pneumoniae is the most common cause of bacterial pneumonia.
Streptococcus pneumoniae is the most common cause of bacterial pneumonia. People who suffer from chronic obstructive pulmonary disease (COPD) or alcoholism most often get pneumonia from Klebsiella pneumoniae and Hemophilus influenzae. Atypical pneumonia, a type of pneumonia that typically occurs during the summer and fall months, is caused by the bacteria Mycoplasma pneumoniae.
People who have Legionnaire's disease caused by the bacterium Legionella pneumoniae (often found in contaminated water supplies and air conditioners) may also develop pneumonia as part of the overall infection. Another type of bacteria responsible for pneumonia is called Chlamydia pneumoniae. Pneumocystis carinii pneumonia is a form of pneumonia that usually affects both lungs and is found in patients with weakened or compromised immune systems from such conditions as cancer and HIV/AIDS and those treated with TNF (tumor necrosis factor) for rheumatoid arthritis.
Viral pneumonias are pneumonias that do not typically respond to antibiotic treatment (in contrast to bacterial pneumonias). Adenoviruses, rhinovirus, influenza virus (flu), respiratory syncytial virus (RSV), and parainfluenza virus are all potential causes of viral pneumonia.
Histoplasmosis, coccidiomycosis, blastomycosis, aspergillosis, and cryptococcosis are fungal infections that can lead to fungal pneumonia. These types of pneumonias are relatively infrequent in the United States.
Nosocomial and others
Organisms that have been exposed to strong antibiotics and have developed resistance are called nosocomial organisms. If they enter the lungs, a person may develop nosocomial pneumonia. Resistant bacteria are often found in nursing homes and hospitals. An example is MRSA, or methicillin-resistant Staph aureus, which can cause skin infections as well as pneumonia. Similarly, outbreaks of the H5N1 influenza (bird flu) virus and severe acute respiratory syndrome (SARS) have resulted in serious pneumonia infections. Anthrax, plague, and tularemia also may cause pneumonia, but their occurrences are rare.
Who gets pneumonia?
Some people are more likely than others to develop pneumonia. Individuals at higher risk include those who:
People who are older than 65 and those that have recently recovered from a cold or flu have an increased risk of developing pneumonia.
- Abuse alcohol.
- Have other medical conditions, such as chronic obstructive pulmonary disease (COPD), emphysema, asthma, or HIV/AIDS.
- Are younger than 1 year of age or older than 65.
- Have a weakened or impaired immune system.
- Take medicines for gastroesophageal reflux disease (GERD).
- Have recently recovered from a cold or influenza infection.
- Are malnourished.
- Have been recently hospitalized in an intensive care unit.
- Have been exposed to certain chemicals or pollutants.
- Are Native Alaskan or certain Native American ethnicity.
- Have any increased risk of breathing mucus or saliva from the nose or mouth, liquids, or food from the stomach into the lungs.
On the next page we look at the symptoms of pneumonia, how it is diagnosed, how it can be prevented and the possible treatment options for pneumonia.