Pneumonia is an infection in one or both lungs. It can be caused by bacteria, viruses, or fungi. Bacterial pneumonia is the most common type in adults. Pneumonia causes inflammation in the air sacs in your lungs, which are called alveoli. The alveoli fill with fluid or pus, making it difficult to breathe.
Normal air sacs and pneumonia affected air sacs
History
Pneumonia has been a common disease throughout human history. The word is from Greek πνεύμων (pneúmōn) meaning “lung”. The symptoms were described by Hippocrates (c. 460 BC – 370 BC). Edwin Klebs was the first to observe bacteria in the airways of persons having died of pneumonia in 1875.
Initial work identifying the two common bacterial causes, Streptococcus pneumoniae and Klebsiella pneumoniae, was performed by Carl Friedländer and Albert Fraenkel in 1882 and 1884, respectively.
Friedländer’s initial work introduced the Gram stain, a fundamental laboratory test still used today to identify and categorize bacteria. Christian Gram’s paper describing the procedure in 1884 helped to differentiate the two bacteria, and showed that pneumonia could be caused by more than one microorganism
Epidemiology
One study estimated that nearly 4 million children died each year of acute respiratory infections in the period from 1980 to 1990. Because of this, the World Health Organization (WHO) set up the Child Health Epidemiology Reference Group (CHERG) to further study the incidence of childhood pneumonia.
CHERG performed systematic reviews to compile pneumonia statistics in children under age 5 for the year 2000. The group found that there were approximately 150 million new episodes of pneumonia in children under 5. Of these 150 million new cases, approximately 4 million occurred in developed countries, while the rest occurred in developing nations.
Pneumonia types
Types by location
Community-acquired pneumonia (CAP) as the name implies, develops outside of the hospital or health-care environment. It is more common than hospital-acquired pneumonia. CAP is most common in winter and affects about 4 million people a year in the U.S.
Hospital-acquired pneumonia (HAP) is acquired when an individual is already hospitalized for another condition. HAP is generally more serious because it develops in ill patients already hospitalized or under medical care for another condition. Being on a ventilator for respiratory support increases the risk of acquiring HAP. Health-care-associated pneumonia is acquired from other health-care settings, like kidney dialysis centers, outpatient clinics, or nursing homes.
Types by germ
Pneumonia can be classified according to the organism that caused the infection.
You can also lower your chances of getting pneumonia by staying away from people who have a cold, measles, or chickenpox and iou may get pneumonia after you have one of these illnesses. Wash your hands often. This helps prevent the spread of viruses and bacteria that may cause pneumonia.
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