Pneumonia

Pneumonia is an condition of the  affecting primarily the small air sacs known as. Typically symptoms include some combination of or dry, , , and. Severity is variable.

Pneumonia is usually caused by infection with es or and less commonly by other s, certain  and conditions such as s. Risk factors include other lung diseases such as, , and , , , a history of , a poor ability to cough such as following a , or a. Diagnosis is often based on the symptoms and. , blood tests, and of the  may help confirm the diagnosis. The disease may be classified by where it was acquired with community, hospital, or health care associated pneumonia.

s to prevent certain types of pneumonia are available. Other methods of prevention include and not smoking. Treatment depends on the underlying cause. Pneumonia believed to be due to bacteria is treated with s. If the pneumonia is severe, the affected person is generally hospitalized. may be used if oxygen levels are low.

Pneumonia affects approximately 450 million people globally (7% of the population) and results in about 4 million deaths per year. Pneumonia was regarded by in the 19th century as "the captain of the men of death". With the introduction of antibiotics and vaccines in the 20th century, survival improved. Nevertheless, in developing countries, and among the very old, the very young, and the, pneumonia remains a. Pneumonia often shortens suffering among those already close to death and has thus been called "the old man's friend".

Signs and symptoms
People with infectious pneumonia often have a, accompanied by , , sharp or stabbing  during deep breaths, and an increased. In elderly people, confusion may be the most prominent sign.

The typical signs and symptoms in children under five are fever, cough, and fast or difficult breathing. Fever is not very specific, as it occurs in many other common illnesses and may be absent in those with severe disease, or in the elderly. In addition, a cough is frequently absent in children less than 2 months old. More severe signs and symptoms in children may include, unwillingness to drink, convulsions, ongoing vomiting, extremes of temperature, or a.

Bacterial and viral cases of pneumonia usually result in similar symptoms. Some causes are associated with classic, but non-specific, clinical characteristics. Pneumonia caused by  may occur with abdominal pain,, or confusion. Pneumonia caused by  is associated with rusty colored sputum. Pneumonia caused by  may have bloody sputum often described as "currant jelly". Bloody sputum (known as ) may also occur with, Gram-negative pneumonia, es and more commonly. Pneumonia caused by  may occur in association with, , or a. Viral pneumonia presents more commonly with than bacterial pneumonia. Pneumonia was historically divided into "typical" and "atypical" based on the belief that the presentation predicted the underlying cause. However, evidence has not supported this distinction, therefore it is no longer emphasized.

Cause
Pneumonia is due to infections caused primarily by or es and less commonly by  and. Although there are over 100 strains of infectious agents identified, only a few are responsible for the majority of the cases. Mixed infections with both viruses and bacteria may occur in roughly 45% of infections in children and 15% of infections in adults. A causative agent may not be isolated in approximately half of cases despite careful testing.

The term pneumonia is sometimes more broadly applied to any condition resulting in of the lungs (caused for example by s, chemical burns or drug reactions); however, this inflammation is more accurately referred to as.

Factors that predispose to pneumonia include, , , , , , , and old age. Additional risk in children include not being, exposure to cigarettes or air pollution, , and poverty. The use of acid-suppressing medications – such as or  – is associated with an increased risk of pneumonia. Approximately 10% of people who require develop, and people with  have an increased risk of developing of. For people with specific variants of, the risk of death is reduced in caused by pneumonia. However, for those with variants, the risk of getting  is increased.

Bacteria
Bacteria are the most-common cause of (CAP), with  isolated in nearly 50% of cases. Other commonly-isolated bacteria include ' in 20%, ' in 13%, and ' in 3% of cases; '; '; '; and. A number of versions of the above infections are becoming more common, including drug-resistant Streptococcus pneumoniae (DRSP) and  (MRSA).

The spreading of organisms is facilitated when risk factors are present. is associated with Streptococcus pneumoniae, s, and Mycobacterium tuberculosis; smoking facilitates the effects of Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, and Legionella pneumophila. Exposure to birds is associated with '; farm animals with '; aspiration of stomach contents with anaerobic organisms; and with  and Staphylococcus aureus. Streptococcus pneumoniae is more common in the winter, and it should be suspected in persons aspirating a large amount of anaerobic organisms.

Viruses
In adults, viruses account for approximately a third and in children for about 15% of pneumonia cases. Commonly-implicated agents include es, es,, (RSV), , and. rarely causes pneumonia, except in groups such as: newborns, persons with cancer, transplant recipients, and people with significant burns. People following or those otherwise- present high rates of  pneumonia. Those with viral infections may be secondarily infected with the bacteria Streptococcus pneumoniae, Staphylococcus aureus, or Haemophilus influenzae, particularly when other health problems are present. Different viruses predominate at different periods of the year; during, for example, influenza may account for over half of all viral cases. Outbreaks of other viruses also occasionally occur, including ' and '.

Fungi
Fungal pneumonia is uncommon, but occurs more commonly in individuals with due to, s, or other medical problems. It is most often caused by ', blastomyces, ', ' (, or PCP), and '. is most common in the, and is most common in the. The number of cases has been increasing in the later half of the 20th century due to increasing travel and rates of immunosuppression in the population. For people infected with, PCP is a common.

Parasites
A variety of s can affect the lungs, including ', ', ', and '. These organisms typically enter the body through direct contact with the skin, ingestion, or via an insect vector. Except for , most parasites do not affect specifically the lungs but involve the lungs secondarily to other sites. Some parasites, in particular those belonging to the Ascaris and Strongyloides genera, stimulate a strong reaction, which may result in. In other infections, such as malaria, lung involvement is due primarily to cytokine-induced systemic inflammation. In the these infections are most common in people returning from travel or in immigrants. Around the world, these infections are most common in the immunodeficient.

Noninfectious
Idiopathic interstitial pneumonia or noninfectious pneumonia is a class of s. They include, , , , , , and. is another rare cause due to entering the lung. These lipids can either be inhaled or from lipids within the body.

Mechanisms
Pneumonia frequently starts as an that moves into the lower respiratory tract. It is a type of (lung inflammation). The normal flora of the upper airway gives protection by competing with pathogens for nutrients. In the lower airways, reflexes of the, actions of s and s are important for protection. Micro of contaminated secretions can infect the lower airways and cause pneumonia. The virulence of the organism, amount of the organisms to start an infection and body immune response against the infection all determines the progress of pneumonia.

Bacterial
Most bacteria enter the lungs via small of organisms residing in the throat or nose. Half of normal people have these small aspirations during sleep. While the throat always contains bacteria, ones reside there only at certain times and under certain conditions. A minority of types of bacteria such as ' and ' reach the lungs via contaminated airborne droplets. Bacteria can spread also via the blood. Once in the lungs, bacteria may invade the spaces between cells and between alveoli, where the s and s (defensive s) attempt to inactivate the bacteria. The neutrophils also release s, causing a general activation of the immune system. This leads to the fever, chills, and fatigue common in bacterial pneumonia. The neutrophils, bacteria, and fluid from surrounding blood vessels fill the alveoli, resulting in the consolidation seen on chest X-ray.

Viral
Viruses may reach the lung by a number of different routes. Respiratory syncytial virus is typically contracted when people touch contaminated objects and then they touch their eyes or nose. Other viral infections occur when contaminated airborne droplets are inhaled through the mouth or nose. Once in the upper airway, the viruses may make their way in the lungs, where they invade the cells lining the airways, alveoli, or. Some viruses such as measles and herpes simplex may reach the lungs via the blood. The invasion of the lungs may lead to varying degrees of cell death. When the immune system responds to the infection, even more lung damage may occur. Primarily s, mainly s, generate the inflammation. As well as damaging the lungs, many viruses simultaneously affect other and thus disrupt other body functions. Viruses also make the body more susceptible to bacterial infections; in this way, bacterial pneumonia can occur at the same time as viral pneumonia.

Diagnosis
Pneumonia is typically diagnosed based on a combination of physical signs and a. In adults with normal vital signs and a normal lung examination the diagnosis is unlikely. However, the underlying cause can be difficult to confirm, as there is no definitive test able to distinguish between bacterial and non-bacterial origin.

has defined pneumonia in children clinically based on either a or difficulty breathing and a rapid respiratory rate, chest indrawing, or a decreased level of consciousness. A rapid respiratory rate is defined as greater than 60 breaths per minute in children under 2 months old, greater than 50 breaths per minute in children 2 months to 1 year old, or greater than 40 breaths per minute in children 1 to 5 years old. In children, low oxygen levels and lower chest indrawing are more than hearing chest  with a  or increased respiratory rate. Grunting and nasal flaring may be other useful signs in children less than five years old. Lack of wheezing is an indicator of  in children with pneumonia, but as an indicator it is not accurate enough to decide whether or not treatment should be used. The presence of chest pain in children with pneumonia doubles the probability of Mycoplasma pneumoniae.

In general, in adults, investigations are not needed in mild cases. There is a very low risk of pneumonia if all s and are normal. In persons requiring hospitalization,, and s – including a , ,  level, and possibly  – are recommended. may help determine the cause and support who should receive antibiotics. Antibiotics is encouraged if procalcitonin level reaches 0.25 μg/L, strongly encouraged if it reaches 0.5 μg/L, and strongly discouraged if the level is below 0.10 μg/L. For those with CRP less than 20 mg/L without convincing evidence of pneumonia, antibiotics are not recommended.

The diagnosis of can be made based on the signs and symptoms; however, confirmation of an influenza infection requires testing. Thus, treatment is frequently based on the presence of influenza in the community or a.

Physical exam
may sometimes reveal, , or low. The respiratory rate may be faster than normal, and this may occur a day or two before other signs. Examination of the chest may be normal, but it may show decreased chest expansion on the affected side. Harsh breath sounds from the larger airways that are transmitted through the inflamed lung are termed breathing and are heard on auscultation with a. (rales) may be heard over the affected area during. may be dulled over the affected lung, and increased, rather than decreased, distinguishes pneumonia from a.

Imaging
A is frequently used in diagnosis. In people with mild disease, imaging is needed only in those with potential complications, those not having improved with treatment, or those in which the cause is uncertain. If a person is sufficiently sick to require hospitalization, a chest radiograph is recommended. Findings do not always match the severity of disease and do not reliably separate between bacterial infection and viral infection.

X-ray presentations of pneumonia may be classified as, bronchopneumonia (also known as lobular pneumonia), and. Bacterial, community-acquired pneumonia classically show of one, which is known as lobar pneumonia. However, findings may vary, and other patterns are common in other types of pneumonia. Aspiration pneumonia may present with bilateral opacities primarily in the bases of the lungs and on the right side. Radiographs of viral pneumonia may appear normal, appear hyper-inflated, have bilateral patchy areas, or present similar to bacterial pneumonia with lobar consolidation. Radiologic findings may not be present in the early stages of the disease, especially in the presence of dehydration, or may be difficult to be interpreted in the or those with a history of lung disease. Complications such as may also be found on chest radiographs. Laterolateral chest radiograph can increase the diagnostic accuracy of lung consolidation and pleural effusion. A can give additional information in indeterminate cases. CT scan can also provide more details in those with an unclear chest radiograph (for example pneumonia in  (COPD)) and is able to exclude  and  and detecting  in those who are not responding to treatments. However, CT scan is more expensive, has a higher dose of radiation, and cannot be done at bedside.

may also be useful in helping to make the diagnosis. Ultrasound is radiation free and can be done at bedside. However, ultrasound requires specific skills to operate the machine and interpret the findings. It may be more accurate than chest X-ray.

Microbiology
In people managed in the community, determining the causative agent is not cost-effective and typically does not alter management. For people who do not respond to treatment, should be considered, and culture for  should be carried out in persons with a chronic productive cough. Microbiological evaluation is also indicated in severe pneumonia, alcoholism,, immunosuppression, HIV infection, and alcohol abuse. Although positive and  culture definitively establish the diagnosis of the type of micro-organism involved, a positive sputum culture has to be interpreted with care for the possibility of  of respiratory tract. Testing for other specific organisms may be recommended during outbreaks, for public health reasons. In those hospitalized for severe disease, both sputum and are recommended, as well as testing the urine for s to Legionella and Streptococcus. Viral infections, can be confirmed via detection of either the virus or its antigens with or  (PCR), among other techniques. Mycoplasma, Legionella, Streptococcus, and Chlamydia can also be detected using PCR techniques on and. The causative agent is determined in only 15% of cases with routine microbiological tests.

Classification
refers to lung ; pneumonia refers to pneumonitis, usually due to infection but sometimes non-infectious, that has the additional feature of. Pneumonia is most commonly classified by where or how it was acquired:, , , , and. It may also be classified by the area of lung affected:, and ; or by the causative organism. Pneumonia in children may additionally be classified based on signs and symptoms as non-severe, severe, or very severe.

The setting in which pneumonia develops is important to treatment, as it correlates to which pathogens are likely suspects, which mechanisms are likely, which antibiotics are likely to work or fail, and which complications can be expected based on the person's health status.

Community
Community-acquired pneumonia (CAP) is acquired in the community, outside of health care facilities. Compared with health care–associated pneumonia, it is less likely to involve bacteria. Although the latter are no longer rare in CAP, they are still less likely.

Healthcare
Health care–associated pneumonia (HCAP) is an infection associated with recent exposure to the system, including hospital, outpatient clinic,,  center,  treatment, or. HCAP is sometimes called MCAP (medical care–associated pneumonia).

Hospital
Hospital-acquired pneumonia is acquired in a, specifically, pneumonia that occurs 48 hours or more after admission, which was not incubating at the time of admission. It is likely to involve s, with higher risk of pathogens. Also, because hospital people are often ill (which is why they are present in the hospital), accompanying disorders are an issue.

Ventilator
occurs in people breathing with the help of. Ventilator-associated pneumonia is specifically defined as pneumonia that arises more than 48 to 72 hours after.

Differential diagnosis
Several diseases can present with similar signs and symptoms to pneumonia, such as: (COPD),, , , , and. Unlike pneumonia, asthma and COPD typically present with, pulmonary edema presents with an abnormal , cancer and bronchiectasis present with a cough of longer duration, and pulmonary emboli presents with acute onset sharp chest pain and. Mild pneumonia should be differentiated from (URTI). Severe pneumonia should be differentiated from. Pulmonary infiltrates that resolved after giving should point to heart failure and  rather than pneumonia. For recurrent pneumonia, underlying lung cancer,, , foreign body, immunosuppression, and hypersensitivity should be sought after.

Prevention
Prevention includes, environmental measures and appropriate treatment of other health problems. It is believed that, if appropriate preventive measures were instituted globally, mortality among children could be reduced by 400,000; and, if proper treatment were universally available, childhood deaths could be decreased by another 600,000.

Vaccination
prevents against certain bacterial and viral pneumonias both in children and adults. s are modestly effective at preventing symptoms of influenza, The (CDC) recommends yearly influenza vaccination for every person 6 months and older. Immunizing health care workers decreases the risk of viral pneumonia among their people.

Vaccinations against ' and ' have good evidence to support their use. There is strong evidence for vaccinating children under the age of 2 against Streptococcus pneumoniae. Vaccinating children against Streptococcus pneumoniae has led to a decreased rate of these infections in adults, because many adults acquire infections from children. A is available for adults, and has been found to decrease the risk of  by 74%, but there is insufficient evidence to suggest using the pneumococcal vaccine to prevent pneumonia or death in the general adult population. The CDC recommends that young children and adults over the age of 65 receive the pneumococcal vaccine, as well as older children or younger adults who have an increased risk of getting pneumococcal disease. The pneumococcal vaccine has been shown to reduce the risk of community acquired pneumonia in people with (COPD), but does not reduce mortality or the risk of hospitalization for people with this condition. People with COPD are suggested to have a pneumococcal vaccination. Other vaccines for which there is support for a protective effect against pneumonia include, , and.

Medications
When influenza outbreaks occur, medications such as or  may help prevent the condition; however are associated with side effects. or decrease the chance that people who are exposed to the virus will develop symptoms; however, it is recommended that potential side effects are taken into account.

Other
and reducing indoor, such as that from cooking indoors with wood or , are both recommended. Smoking appears to be the single biggest risk factor for in otherwise-healthy adults. Hand hygiene and coughing into one's sleeve may also be effective preventative measures. Wearing by the sick may also prevent illness.

Appropriately treating underlying illnesses (such as, , and ) can decrease the risk of pneumonia. In children less than 6 months of age, exclusive breast feeding reduces both the risk and severity of disease. In those with HIV/AIDS and a CD4 count of less than 200 cells/uL the antibiotic decreases the risk of  and is also useful for prevention in those that are immunocomprised but do not have HIV.

Testing pregnant women for and , and administering  treatment, if needed, reduces rates of pneumonia in infants; preventive measures for HIV transmission from mother to child may also be efficient. Suctioning the mouth and throat of infants with -stained has not been found to reduce the rate of  and may cause potential harm, thus this practice is not recommended in the majority of situations. In the frail elderly good oral health care may lower the risk of aspiration pneumonia. supplementation in children 2 months to five years old appears to reduce rates of pneumonia.

For people with low levels of in their diet or blood, taking vitamin C supplements may be suggested to decrease the risk of pneumonia, although there is no strong evidence of benefit. There is insufficient evidence to recommend that the general population take vitamin C to prevent pneumonia.

For adults and children in the hospital who require a respirator, there is no strong evidence indicating a difference between s and for preventing pneumonia. There is no good evidence that one approach to mouth care is better than others in preventing nursing home acquired pneumonia.

Management
by mouth, rest, simple, and fluids usually suffice for complete resolution. However, those with other medical conditions, the elderly, or those with significant trouble breathing may require more advanced care. If the symptoms worsen, the pneumonia does not improve with home treatment, or complications occur, hospitalization may be required. Worldwide, approximately 7–13% of cases in children result in hospitalization, whereas in the developed world between 22 and 42% of adults with community-acquired pneumonia are admitted. The score is useful for determining the need for admission in adults. If the score is 0 or 1, people can typically be managed at home; if it is 2, a short hospital stay or close follow-up is needed; if it is 3–5, hospitalization is recommended. In children those with or oxygen saturations of less than 90% should be hospitalized. The utility of in pneumonia has not yet been determined. Over-the-counter has not been found to be effective, nor has the use of  in children. There is insufficient evidence for. There is no strong evidence to recommend that children who have non-measles related pneumonia take supplements. Vitamin D, as of 2018 is of unclear benefit in children.

Pneumonia can cause severe illness in a number of ways, and pneumonia with evidence of organ dysfunction may require admission for observation and specific treatment. The main impact is on the respiratory and the circulatory system. not responding to normal oxygen therapy may require delivered through nasal cannulae,, or in severe cases  through an endotracheal tube. With regards to circulatory problems as part of, evidence of poor blood flow or low blood pressure is initially treated with 30 ml/kg of infused intravenously. In situations where fluids alone are ineffective, medication may be required.

Bacterial
s improve outcomes in those with bacterial pneumonia. First dose of antibiotics should be given as soon as possible. Increased use of antibiotics, however, may lead to the development of strains of bacteria. Antibiotic choice depends initially on the characteristics of the person affected, such as age, underlying health, and the location the infection was acquired. Antibiotic use is also associated with side effects such as nausea, diarrhea, dizziness, taste distortion, or headaches. In the UK, with  is recommended as the first line for, with  or  as alternatives. In, where the "atypical" forms of community-acquired pneumonia are more common, s (such as or ), and doxycycline have displaced amoxicillin as first-line outpatient treatment in adults. In children with mild or moderate symptoms, amoxicillin taken by mouth remains the first line. The use of in uncomplicated cases is discouraged due to concerns about side-effects and generating resistance in light of there being no greater clinical benefit.

For those who require hospitalization and caught their pneumonia in the community the use of a β-lactam such as plus  such as  or a fluoroquinolones is recommended. Antibiotics by mouth and by injection appear to be similarly effective in children with severe pneumonia.

The duration of treatment has traditionally been seven to ten days, but increasing evidence suggests that shorter courses (3–5 days) may be effective for certain types of pneumonia and may reduce the risk of antibiotic resistance. For pneumonia that is associated with a ventilator caused by non-fermenting Gram-negative bacilli (NF-GNB), a shorter course of antibiotics increases the risk of that pneumonia will return. Recommendations for include third- and fourth-generation, s, s, s, and. These antibiotics are often given and used in combination. In those treated in hospital, more than 90% improve with the initial antibiotics. For people with ventilator-acquired pneumonia, the choice of antibiotic therapy will depend on the person's risk of being infected with a strain of bacteria that is. Once clinically stable, intravenous antibiotics should be switched to oral antibiotics. For those with  (MRSA) or Legionella infections, prolonged antibiotics may be beneficial.

The addition of s to standard antibiotic treatment appears to improve outcomes, reducing death and morbidity for adults with severe community acquired pneumonia, and reducing death for adults and children with non-severe community acquired pneumonia. Side effects associated with the use of corticosteroids include high blood sugar. They are therefore recommended in adults with severe community acquired pneumonia. There is some evidence that adding corticosteroids to the standard PCP pneumonia treatment may be beneficial for people who are infected with HIV.

The use of granulocyte colony stimulating factor (G-CSF) along with antibiotics does not appear to reduce mortality and routine use for treating pneumonia is not supported by evidence.

Viral
may be used to treat caused by influenza viruses ( and ). No specific medications are recommended for other types of community acquired viral pneumonias including, , , and  virus. Influenza A may be treated with or, while influenza A or B may be treated with ,  or. These are of most benefit if they are started within 48 hours of the onset of symptoms. Many strains of influenza A, also known as  or "bird flu", have shown resistance to rimantadine and amantadine. The use of antibiotics in viral pneumonia is recommended by some experts, as it is impossible to rule out a complicating bacterial infection. The recommends that antibiotics be withheld in those with mild disease. The use of s is controversial.

Aspiration
In general, is treated conservatively with antibiotics indicated only for. The choice of antibiotic will depend on several factors, including the suspected causative organism and whether pneumonia was acquired in the community or developed in a hospital setting. Common options include, a combination of a and , or an. s are sometimes used in aspiration pneumonia, but there is limited evidence to support their effectiveness.

Follow-up
The recommends that a follow-up chest radiograph is taken in people with persistent symptoms, smokers, and people older than 50. American guidelines vary, from generally recommending a follow-up chest radiograph to not mentioning any follow-up.

Prognosis
With treatment, most types of bacterial pneumonia will stabilize in 3–6 days. It often takes a few weeks before most symptoms resolve. X-ray finding typically clear within four weeks and mortality is low (less than 1%). In the elderly or people with other lung problems, recovery may take more than 12 weeks. In persons requiring hospitalization, mortality may be as high as 10%, and in those requiring intensive care it may reach 30–50%. Pneumonia is the most common that causes death. Before the advent of antibiotics, mortality was typically 30% in those that were hospitalized. However, for those whose lung condition deteriorates within 72 hours, the problem is usually due to sepsis. If pneumonia deteriorates after 72 hours, it could be due to or excerbation of other underlying co-morbidities. About 10% of those discharged from hospital are readmitted due to underlying co-morbidities such as heart, lung, or neurology disorders, or due to new onset of pneumonia.

Complications may occur in particular in the elderly and those with underlying health problems. This may include, among others:, , , , , and worsening of underlying health problems.

Clinical prediction rules
Clinical prediction rules have been developed to more objectively predict outcomes of pneumonia. These rules are often used in deciding whether or not to hospitalize the person.
 * (or PSI Score)
 * score, which takes into account the severity of symptoms, any underlying diseases, and age

Pleural effusion, empyema, and abscess
In pneumonia, a may form in the. Occasionally, microorganisms will infect this fluid, causing an. To distinguish an empyema from the more common simple, the fluid may be collected with a needle , and examined. If this shows evidence of empyema, complete drainage of the fluid is necessary, often requiring a. In severe cases of empyema, may be needed. If the infected fluid is not drained, the infection may persist, because antibiotics do not penetrate well into the pleural cavity. If the fluid is sterile, it must be drained only if it is causing symptoms or remains unresolved.

In rare circumstances, bacteria in the lung will form a pocket of infected fluid called a. Lung abscesses can usually be seen with a chest X-ray but frequently require a chest CT scan to confirm the diagnosis. Abscesses typically occur in, and often contain several types of bacteria. Long-term antibiotics are usually adequate to treat a lung abscess, but sometimes the abscess must be drained by a or.

Respiratory and circulatory failure
Pneumonia can cause respiratory failure by triggering (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 for survival. Other causes of circulatory failure are, , and increased coagulability.

is a potential complication of pneumonia but occurs usually in people with poor immunity or. The organisms most commonly involved are Streptococcus pneumoniae, Haemophilus influenzae, and Klebsiella pneumoniae. Other causes of the symptoms should be considered such as a or a.

Epidemiology
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 than in the. 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. Many of these deaths occur in the period. The 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. 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
Pneumonia has been a common disease throughout human history. The word is from Greek πνεύμων (pneúmōn) meaning "lung". The symptoms were described by (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. (1135–1204 AD) observed: "The basic symptoms that occur in pneumonia and that are never lacking are as follows: acute fever, sticking pain in the side, short rapid breaths, serrated  and cough." This clinical description is quite similar to those found in modern textbooks, and it reflected the extent of medical knowledge through the into the 19th century.

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 and  in 1882 and 1884, respectively. Friedländer's initial work introduced the, a fundamental laboratory test still used today to identify and categorize bacteria. '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.

Sir, 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 as one of the leading causes of death in this time. This phrase was originally coined by 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.

Several developments in the 1900s improved the outcome for those with pneumonia. With the advent of 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  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.

Awareness
Due to the relatively low awareness of the disease, 12 November was declared as the annual, 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, 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.