by a surgeon or radiologist. respiratory and circulatory failure pneumonia can cause respiratory failure by triggering acute respiratory distress syndrome (ards), which results from a combination of infection and inflammatory response. the lungs quickly fill with fluid and become stiff. this stiffness, combined with severe difficulties extracting oxygen due to the alveolar fluid, may require long periods of mechanical ventilation for survival. other causes of circulatory failure are hypoxemia, inflammation, and increased coagulability. sepsis is a potential complication of pneumonia but usually occurs in people with poor immunity or hyposplenism. the organisms most commonly involved are streptococcus pneumoniae, haemophilus influenzae, and klebsiella pneumoniae. other causes of the symptoms should be considered such as a myocardial infarction or a pulmonary embolism. epidemiology main article: epidemiology of pneumonia deaths from lower respiratory infections per million persons in 2012 24–120 121–151 152–200 201–241 242–345 346–436 437–673 674–864 865–1,209 1,210–2,085 disability-adjusted life year for lower respiratory infections per 100,000 inhabitants in 2004 no data less than 100 100–700 700–1,400 1,400–2,100 2,100–2,800 2,800–3,500 3,500–4,200 4,200–4,900 4,900–5,600 5,600–6,300 6,300–7,000 more than 7,000 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 world's total death) yearly. rates are greatest in children less than five, and adults older than 75 years. it occurs about five times more frequently in the developing world than in the developed world. viral pneumonia accounts for about 200 million cases. in the united states, as of 2009, pneumonia is the 8th leading cause of death. children in 2008, pneumonia occurred in approximately 156 million children (151 million in the developing world and 5 million in the developed world). in 2010, it resulted in 1.3 million deaths, or 18% of all deaths in those under five years, of which 95% occurred 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 is due to pneumonia. approximately half of these deaths can be prevented, as they are caused by the bacteria for which an effective vaccine is available. the idsa has recommended that children and infants with symptoms of cap should be hospitalized so they have access to pediatric nursing care. in 2011, pneumonia was the most common reason for admission to the hospital after an emergency department visit in the u.s. for infants and children. history wpa poster, 1936/1937 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. 460–370 bc): "peripneumonia, and pleuritic affections, are to be thus observed: if the fever be acute, and if there be pains on either side, or in both, and if expiration be if cough be present, and the sputa expectorated be of a blond or livid color, or likewise thin, frothy, and florid, or having any other character different from the common... when pneumonia is at its height, the case is beyond remedy if he is not purged, and it is bad if he has dyspnoea, and urine that is thin and acrid, and if sweats come out about the neck and head, for such sweats are bad, as proceeding from the suffocation, rales, and the violence of the disease which is obtaining the upper hand." however, hippocrates referred to pneumonia as a disease "named by the ancients". he also reported the results of surgical drainage of empyemas. maimonides (1135–1204 ad) observed: "the basic symptoms that occur in pneumonia and that are never lacking are as follows: acute fever, sticking pleuritic pain in the side, short rapid breaths, serrated pulse and cough." this clinical description is quite similar to those found in modern textbooks, and it reflected the extent of medical knowledge through the middle ages into the 19th century. 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. in 1887, jaccond demonstrated pneumonia may be caused by opportunistic bacteria always present in the lung. sir william osler, known as "the father of modern medicine", appreciated the death and disability caused by pneumonia, describing it as the "captain of the men of death" in 1918, as it had overtaken tuberculosis as one of the leading causes of death at the time. this phrase was originally coined by john bunyan in reference to "consumption" (tuberculosis). osler also described pneumonia as "the old man's friend" as death was often quick and painless when there were much slower and more painful ways to die. viral pneumonia was first described by hobart reimann in 1938. reimann, chairman of the department of medicine at jefferson medical college, had established the practice of routinely typing the pneumococcal organism in cases where pneumonia presented. out of this work, the distinction between viral and bacterial strains was noticed. several developments in the 1900s improved the outcome for those with pneumonia. with the advent of penicillin and other antibiotics, modern surgical techniques, and intensive care in the 20th century, mortality from pneumonia, which had approached 30%, dropped precipitously in the developed world. vaccination of infants against haemophilus influenzae type b began in 1988 and led to a dramatic decline in cases shortly thereafter. vaccination against streptococcus pneumoniae in adults began in 1977, and in children in 2000, resulting in a similar decline. society and culture awareness due to the relatively low awareness of the disease, 12 november was declared as the annual world pneumonia day, a day for concerned citizens and policy makers to take action against the disease, in 2009. costs the global economic cost of community-acquired pneumonia has been estimated at $17 billion annually. other estimates are considerably higher. in 2012 the estimated aggregate costs of treating pneumonia in the united states were $20 billion; the median cost of a single pneumonia-related hospitalization is over $15,000. according to data released by the centers for medicare and medicaid services, average 2012 hospital charges for inpatient treatment of uncomplicated pneumonia in the u.s. were $24,549 and ranged as high as $124,000. the average cost of an emergency room consult for pneumonia was $943 and the average cost for medication was $66. aggregate annual costs of treating pneumonia in europe have been estimated at €10 billion.