Pneumonia is a common illness affecting approximately 450 million people a year and occurring in all parts of the world. It is a major cause of death among all age groups resulting in 4 million deaths (7% of the worlds yearly total).
Rates are greatest in children less than five and adults older than 75 years of age. It occurs about five times more frequently in the developing world versus the developed world. Viral pneumonia accounts for about 200 million cases.
In 2008 pneumonia occurred in approximately 156 million children (151 million in the developing world and 5 million in the developed world). It resulting in 1.6 million deaths or 28–34% of all deaths in those under five years of age of which 95% occur in the developing world. Countries with the greatest burden of disease include: India (43 million), China (21 million) and Pakistan (10 million).
It is the leading cause of death among children in low income countries. Many of these deaths occur in the newborn period. The World Health Organization estimates that one in three newborn infant deaths are due to pneumonia. Approximately half of these cases and deaths are theoretically preventable, being caused by the bacteria for which an effective vaccine is available.
In the United Kingdom, the annual incidence rate of pneumonia is approximately 6 cases per 1000 people in individuals aged 18–39 years. For those over 75 years of age, the incidence rate rises to 75 cases per 1000 people. Roughly 20–40% of individuals who contract pneumonia require hospital admission, with between 5–10% of these admitted to a critical care unit. The case fatality rate in the UK is around 5–10%.
In the United States, community-acquired pneumonia affects 5.6 million people per year, and ranks 6th among leading causes of death. In 2009, there were approximately 1.86 million emergency department encounters for pneumonia in the United States. In 2011, pneumonia was the second-most common reason for hospitalization in the U.S., with approximately 1.1 million stays—a rate of 36 stays per 10,000 population.
Pneumonia was one of the top ten most expensive conditions seen during inpatient hospitalizations in the U.S. in 2011, with an aggregate cost of nearly $10.6 billion for 1.1 million stays. In 2012, a study of Medicaid-covered and uninsured hospital stays in the United States in 2012, pneumonia was the second most common diagnosis for Medicaid-covered and uninsured hospital stays in the United States (behind mood disorders, at 3.7% for Medicaid stays and 2.4% for uninsured stays).
More cases of community acquired pneumonia occur during the winter months than at other times of the year. Pneumonia occurs more commonly in males than in females, and more often among Blacks than Caucasians, partly due to quantitative differences in synthesizing Vitamin D after exposure to sunlight.
Individuals with underlying chronic illnesses, such as Alzheimer's disease, cystic fibrosis, emphysema, and immune system problems as well as tobacco smokers, alcoholics, and individuals who are hospitalized for any reason, are at significantly increased risk of contracting, and having repeated bouts of, pneumonia.