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Pneumonia causes the lungs’ air sacs AKA alveoli to become inflamed and fill up with fluid or pus. This can make it hard for oxygen you breathe in to get into your bloodstream.

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Some treatments include Antibiotics, which stops the growth of or kills bacteria. Penicillin, which also stops the growth of bacteria.

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In the United States, the annual incidence is 24.8 cases per 10,000 adults with higher rates as age increases.

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Common symptoms of pneumonia includes sharp pains in the chest, fever, chills, dehydration, fatigue, loss of appetite, malaise, clammy skin, or sweating.

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https://youtu.be/IAQp2Zuqevc

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The main cause of pneumonia is caused by viruses.

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https://www.mayoclinic.org/diseases-conditions/pneumonia/symptoms-causes/syc-20354204

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Overview

Pneumonia is an infection that inflames the air sacs in one or both lungs. The air sacs may fill with fluid or pus (purulent material), causing cough with phlegm or pus, fever, chills, and difficulty breathing. A variety of organisms, including bacteria, viruses and fungi, can cause pneumonia.

Pneumonia can range in seriousness from mild to life-threatening. It is most serious for infants and young children, people older than age 65, and people with health problems or weakened immune systems.

Symptoms

The signs and symptoms of pneumonia vary from mild to severe, depending on factors such as the type of germ causing the infection, and your age and overall health. Mild signs and symptoms often are similar to those of a cold or flu, but they last longer.

Signs and symptoms of pneumonia may include:

Chest pain when you breathe or cough

Confusion or changes in mental awareness (in adults age 65 and older)

Cough, which may produce phlegm

Fatigue

Fever, sweating and shaking chills

Lower than normal body temperature (in adults older than age 65 and people with weak immune systems)

Nausea, vomiting or diarrhea

Shortness of breath

Newborns and infants may not show any sign of the infection. Or they may vomit, have a fever and cough, appear restless or tired and without energy, or have difficulty breathing and eating.

When to see a doctor

See your doctor if you have difficulty breathing, chest pain, persistent fever of 102 F (39 C) or higher, or persistent cough, especially if you're coughing up pus.

It's especially important that people in these high-risk groups see a doctor:

Adults older than age 65

Children younger than age 2 with signs and symptoms

People with an underlying health condition or weakened immune system

People receiving chemotherapy or taking medication that suppresses the immune system

For some older adults and people with heart failure or chronic lung problems, pneumonia can quickly become a life-threatening condition.

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Causes

Many germs can cause pneumonia. The most common are bacteria and viruses in the air we breathe. Your body usually prevents these germs from infecting your lungs. But sometimes these germs can overpower your immune system, even if your health is generally good.

Pneumonia is classified according to the types of germs that cause it and where you got the infection.

Community-acquired pneumonia

Community-acquired pneumonia is the most common type of pneumonia. It occurs outside of hospitals or other health care facilities. It may be caused by:

Bacteria. The most common cause of bacterial pneumonia in the U.S. is Streptococcus pneumoniae. This type of pneumonia can occur on its own or after you've had a cold or the flu. It may affect one part (lobe) of the lung, a condition called lobar pneumonia.

Bacteria-like organisms. Mycoplasma pneumoniae also can cause pneumonia. It typically produces milder symptoms than do other types of pneumonia. Walking pneumonia is an informal name given to this type of pneumonia, which typically isn't severe enough to require bed rest.

Fungi. This type of pneumonia is most common in people with chronic health problems or weakened immune systems, and in people who have inhaled large doses of the organisms. The fungi that cause it can be found in soil or bird droppings and vary depending upon geographic location.

Viruses, including COVID-19. Some of the viruses that cause colds and the flu can cause pneumonia. Viruses are the most common cause of pneumonia in children younger than 5 years. Viral pneumonia is usually mild. But in some cases it can become very serious. Coronavirus 2019 (COVID-19) may cause pneumonia, which can become severe.

Hospital-acquired pneumonia

Some people catch pneumonia during a hospital stay for another illness. Hospital-acquired pneumonia can be serious because the bacteria causing it may be more resistant to antibiotics and because the people who get it are already sick. People who are on breathing machines (ventilators), often used in intensive care units, are at higher risk of this type of pneumonia.

Health care-acquired pneumonia

Health care-acquired pneumonia is a bacterial infection that occurs in people who live in long-term care facilities or who receive care in outpatient clinics, including kidney dialysis centers. Like hospital-acquired pneumonia, health care-acquired pneumonia can be caused by bacteria that are more resistant to antibiotics.

Aspiration pneumonia

Aspiration pneumonia occurs when you inhale food, drink, vomit or saliva into your lungs. Aspiration is more likely if something disturbs your normal gag reflex, such as a brain injury or swallowing problem, or excessive use of alcohol or drugs.

Risk factors

Pneumonia can affect anyone. But the two age groups at highest risk are:

Children who are 2 years old or younger

People who are age 65 or older

Other risk factors include:

Being hospitalized. You're at greater risk of pneumonia if you're in a hospital intensive care unit, especially if you're on a machine that helps you breathe (a ventilator).

Chronic disease. You're more likely to get pneumonia if you have asthma, chronic obstructive pulmonary disease (COPD) or heart disease.

Smoking. Smoking damages your body's natural defenses against the bacteria and viruses that cause pneumonia.

Weakened or suppressed immune system. People who have HIV/AIDS, who've had an organ transplant, or who receive chemotherapy or long-term steroids are at risk.

Complications

Even with treatment, some people with pneumonia, especially those in high-risk groups, may experience complications, including:

Bacteria in the bloodstream (bacteremia). Bacteria that enter the bloodstream from your lungs can spread the infection to other organs, potentially causing organ failure.

Difficulty breathing. If your pneumonia is severe or you have chronic underlying lung diseases, you may have trouble breathing in enough oxygen. You may need to be hospitalized and use a breathing machine (ventilator) while your lung heals.

Fluid accumulation around the lungs (pleural effusion). Pneumonia may cause fluid to build up in the thin space between layers of tissue that line the lungs and chest cavity (pleura). If the fluid becomes infected, you may need to have it drained through a chest tube or removed with surgery.

Lung abscess. An abscess occurs if pus forms in a cavity in the lung. An abscess is usually treated with antibiotics. Sometimes, surgery or drainage with a long needle or tube placed into the abscess is needed to remove the pus.

Prevention

To help prevent pneumonia:

Get vaccinated. Vaccines are available to prevent some types of pneumonia and the flu. Talk with your doctor about getting these shots. The vaccination guidelines have changed over time so make sure to review your vaccination status with your doctor even if you recall previously receiving a pneumonia vaccine.

Make sure children get vaccinated. Doctors recommend a different pneumonia vaccine for children younger than age 2 and for children ages 2 to 5 years who are at particular risk of pneumococcal disease. Children who attend a group child care center should also get the vaccine. Doctors also recommend flu shots for children older than 6 months.

Practice good hygiene. To protect yourself against respiratory infections that sometimes lead to pneumonia, wash your hands regularly or use an alcohol-based hand sanitizer.

Don't smoke. Smoking damages your lungs' natural defenses against respiratory infections.

Keep your immune system strong. Get enough sleep, exercise regularly and eat a healthy diet.

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Pneumonia - Learn about the symptoms, causes and treatment of this serious lung infection.

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https://en.m.wikipedia.org/wiki/Pneumonia

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Pneumonia is an inflammatory condition of the lung primarily affecting the small air sacs known as alveoli.[3][14] Symptoms typically include some combination of productive or dry cough, chest pain, fever, and difficulty breathing.[15] The severity of the condition is variable.[15]

Pneumonia

Other names

Pneumonitis

Chest X-ray of a pneumonia caused by influenza and Haemophilus influenzae, with patchy consolidations, mainly in the right upper lobe (arrow)

Pronunciation

Specialty

Pulmonology, infectious disease

Symptoms

Cough, shortness of breath, chest pain, fever[1]

Duration

Few weeks[2]

Causes

Bacteria, virus, aspiration[3][4]

Risk factors

Cystic fibrosis, COPD, sickle cell disease, asthma, diabetes, heart failure, history of smoking, very young age, older age[5][6][7]

Diagnostic method

Based on symptoms, chest X-ray[8]

Differential diagnosis

COPD, asthma, pulmonary edema, pulmonary embolism[9]

Prevention

Vaccines, handwashing, not smoking[10]

Medication

Antibiotics, antivirals, oxygen therapy[11][12]

Frequency

450 million (7%) per year[12][13]

Deaths

Four million per year[12][13]

Pneumonia is usually caused by infection with viruses or bacteria, and less commonly by other microorganisms.[a] Identifying the responsible pathogen can be difficult. Diagnosis is often based on symptoms and physical examination.[8] Chest X-rays, blood tests, and culture of the sputum may help confirm the diagnosis.[8] The disease may be classified by where it was acquired, such as community- or hospital-acquired or healthcare-associated pneumonia.[18]

Risk factors for pneumonia include cystic fibrosis, chronic obstructive pulmonary disease (COPD), sickle cell disease, asthma, diabetes, heart failure, a history of smoking, a poor ability to cough (such as following a stroke), and a weak immune system.[5][7]

Vaccines to prevent certain types of pneumonia (such as those caused by Streptococcus pneumoniae bacteria, linked to influenza, or linked to COVID-19) are available.[10] Other methods of prevention include hand washing to prevent infection, and not smoking.[10]

Treatment depends on the underlying cause.[19] Pneumonia believed to be due to bacteria is treated with antibiotics.[11] If the pneumonia is severe, the affected person is generally hospitalized.[19] Oxygen therapy may be used if oxygen levels are low.[11]

Each year, pneumonia affects about 450 million people globally (7% of the population) and results in about 4 million deaths.[12][13] With the introduction of antibiotics and vaccines in the 20th century, survival has greatly improved.[12] Nevertheless, pneumonia remains a leading cause of death in developing countries, and also among the very old, the very young, and the chronically ill.[12][20] Pneumonia often shortens the period of suffering among those already close to death and has thus been called "the old man's friend".[21]

Video summary (script)

Symptoms frequency[22]

Symptom

Frequency

Cough

79-91%

Fatigue

90%

Fever

71-75%

Shortness of breath

67-75%

Sputum

60-65%

Chest pain

39-49%

Main symptoms of infectious pneumonia

People with infectious pneumonia often have a productive cough, fever accompanied by shaking chills, shortness of breath, sharp or stabbing chest pain during deep breaths, and an increased rate of breathing.[9] In elderly people, confusion may be the most prominent sign.[9]

The typical signs and symptoms in children under five are fever, cough, and fast or difficult breathing.[23] Fever is not very specific, as it occurs in many other common illnesses and may be absent in those with severe disease, malnutrition or in the elderly. In addition, a cough is frequently absent in children less than 2 months old.[23] More severe signs and symptoms in children may include blue-tinged skin, unwillingness to drink, convulsions, ongoing vomiting, extremes of temperature, or a decreased level of consciousness.[23][24]

Bacterial and viral cases of pneumonia usually result in similar symptoms.[25] Some causes are associated with classic, but non-specific, clinical characteristics. Pneumonia caused by Legionella may occur with abdominal pain, diarrhea, or confusion.[26] Pneumonia caused by Streptococcus pneumoniae is associated with rusty colored sputum.[27] Pneumonia caused by Klebsiella may have bloody sputum often described as "currant jelly".[22] Bloody sputum (known as hemoptysis) may also occur with tuberculosis, Gram-negative pneumonia, lung abscesses and more commonly acute bronchitis.[24] Pneumonia caused by Mycoplasma pneumoniae may occur in association with swelling of the lymph nodes in the neck, joint pain, or a middle ear infection.[24] Viral pneumonia presents more commonly with wheezing than bacterial pneumonia.[25] Pneumonia was historically divided into "typical" and "atypical" based on the belief that the presentation predicted the underlying cause.[28] However, evidence has not supported this distinction, therefore it is no longer emphasized.[28]

The bacterium Streptococcus pneumoniae, a common cause of pneumonia, imaged by an electron microscope

Pneumonia is due to infections caused primarily by bacteria or viruses and less commonly by fungi and parasites. Although more than 100 strains of infectious agents have been identified, only a few are responsible for the majority of cases. Mixed infections with both viruses and bacteria may occur in roughly 45% of infections in children and 15% of infections in adults.[12] A causative agent may not be isolated in about half of cases despite careful testing.[21] In an active population-based surveillance for community-acquired pneumonia requiring hospitalization in five hospitals in Chicago and Nashville from January 2010 through June 2012, 2259 patients were identified who had radiographic evidence of pneumonia and specimens that could be tested for the responsible pathogen.[29] Most patients (62%) had no detectable pathogens in their sample, and unexpectedly, respiratory viruses were detected more frequently than bacteria.[29] Specifically, 23% had one or more viruses, 11% had one or more bacteria, 3% had both bacterial and viral pathogens, and 1% had a fungal or mycobacterial infection. "The most common pathogens were human rhinovirus (in 9% of patients), influenza virus (in 6%), and Streptococcus pneumoniae (in 5%)."[29]

The term pneumonia is sometimes more broadly applied to any condition resulting in inflammation of the lungs (caused for example by autoimmune diseases, chemical burns or drug reactions); however, this inflammation is more accurately referred to as pneumonitis.[16][17]

Factors that predispose to pneumonia include smoking, immunodeficiency, alcoholism, chronic obstructive pulmonary disease, sickle cell disease (SCD), asthma, chronic kidney disease, liver disease, and biological aging.[24][30][7] Additional risks in children include not being breastfed, exposure to cigarette smoke and other air pollution, malnutrition, and poverty.[31] The use of acid-suppressing medications - such as proton-pump inhibitors or H2 blockers - is associated with an increased risk of pneumonia.[32] Approximately 10% of people who require mechanical ventilation develop ventilator-associated pneumonia,[33] and people with a gastric feeding tube have an increased risk of developing aspiration pneumonia.[34] Moreover, the misplacement of a feeding tube can lead to aspiration pneumonia. 28% of tube malposition results in pneumonia.[35][36] As with Avanos Medical's feeding tube placement system, the CORTRAK* 2 EAS, which was recalled in May 2022 by the FDA due to adverse events reported, including pneumonia, caused a total of 60 injuries and 23 patient deaths, as communicated by the FDA.[37][38][39] For people with certain variants of the FER gene, the risk of death is reduced in sepsis caused by pneumonia. However, for those with TLR6 variants, the risk of getting Legionnaires' disease is increased.[40]

Bacteria

Cavitating pneumonia due to MRSA as seen on a CT scan

Bacteria are the most common cause of community-acquired pneumonia (CAP), with Streptococcus pneumoniae isolated in nearly 50% of cases.[41][42] Other commonly isolated bacteria include Haemophilus influenzae in 20%, Chlamydophila pneumoniae in 13%, and Mycoplasma pneumoniae in 3% of cases;[41] Staphylococcus aureus; Moraxella catarrhalis; and Legionella pneumophila.[21] A number of drug-resistant versions of the above infections are becoming more common, including drug-resistant Streptococcus pneumoniae (DRSP) and methicillin-resistant Staphylococcus aureus (MRSA).[24]

The spreading of organisms is facilitated by certain risk factors.[21] Alcoholism is associated with Streptococcus pneumoniae, anaerobic organisms, and Mycobacterium tuberculosis; smoking facilitates the effects of Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, and Legionella pneumophila. Exposure to birds is associated with Chlamydia psittaci; farm animals with Coxiella burnetti; aspiration of stomach contents with anaerobic organisms; and cystic fibrosis with Pseudomonas aeruginosa and Staphylococcus aureus.[21] Streptococcus pneumoniae is more common in the winter,[21] and it should be suspected in persons aspirating a large number of anaerobic organisms.[24]

Viruses

In adults, viruses account for about one third of pneumonia cases,[12] and in children for about 15% of them.[43] Commonly implicated agents include rhinoviruses, coronaviruses, influenza virus, respiratory syncytial virus (RSV), adenovirus, and parainfluenza.[12][44] Herpes simplex virus rarely causes pneumonia, except in groups such as newborns, persons with cancer, transplant recipients, and people with significant burns.[45] After organ transplantation or in otherwise immunocompromised persons, there are high rates of cytomegalovirus pneumonia.[43][45] 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.[24][43] Different viruses predominate at different times of the year; during flu season, for example, influenza may account for more than half of all viral cases.[43] Outbreaks of other viruses also occur occasionally, including hantaviruses and coronaviruses.[43] Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can also result in pneumonia.[46]

Fungi

Fungal pneumonia is uncommon, but occurs more commonly in individuals with weakened immune systems due to AIDS, immunosuppressive drugs, or other medical problems.[21][47] It is most often caused by Histoplasma capsulatum, Blastomyces, Cryptococcus neoformans, Pneumocystis jiroveci ( pneumocystis pneumonia, or PCP), and Coccidioides immitis. Histoplasmosis is most common in the Mississippi River basin, and coccidioidomycosis is most common in the Southwestern United States.[21] The number of cases of fungal pneumonia has been increasing in the latter half of the 20th century due to increasing travel and rates of immunosuppression in the population.[47] For people infected with HIV/AIDS, PCP is a common opportunistic infection.[48]

Parasites

A variety of parasites can affect the lungs, including Toxoplasma gondii, Strongyloides stercoralis, Ascaris lumbricoides, and Plasmodium malariae.[49] These organisms typically enter the body through direct contact with the skin, ingestion, or via an insect vector.[49] Except for Paragonimus westermani, most parasites do not specifically affect the lungs but involve the lungs secondarily to other sites.[49] Some parasites, in particular those belonging to the Ascaris and Strongyloides genera, stimulate a strong eosinophilic reaction, which may result in eosinophilic pneumonia.[49] In other infections, such as malaria, lung involvement is due primarily to cytokine-induced systemic inflammation.[49] In the developed world, these infections are most common in people returning from travel or in immigrants.[49] Around the world, parasitic pneumonia is most common in the immunodeficient.[50]

Noninfectious

Idiopathic interstitial pneumonia or noninfectious pneumonia[51] is a class of diffuse lung diseases. They include diffuse alveolar damage, organizing pneumonia, nonspecific interstitial pneumonia, lymphocytic interstitial pneumonia, desquamative interstitial pneumonia, respiratory bronchiolitis interstitial lung disease, and usual interstitial pneumonia.[52] Lipoid pneumonia is another rare cause due to lipids entering the lung.[53] These lipids can either be inhaled or spread to the lungs from elsewhere in the body.[53]

Pneumonia is typically diagnosed based on a combination of physical signs and often a chest X-ray.[60] In adults with normal vital signs and a normal lung examination, the diagnosis is unlikely.[61] However, the underlying cause can be difficult to confirm, as there is no definitive test able to distinguish between bacterial and non-bacterial cause.[12][60] The overall impression of a physician appears to be at least as good as decision rules for making or excluding the diagnosis.[62]

Diagnosis in children

In children, low oxygen levels and lower chest indrawing are more sensitive than hearing chest crackles with a stethoscope or increased respiratory rate.[64] Grunting and nasal flaring may be other useful signs in children less than five years old.[65]

Lack of wheezing is an indicator of Mycoplasma pneumoniae in children with pneumonia, but as an indicator it is not accurate enough to decide whether or not macrolide treatment should be used.[66] The presence of chest pain in children with pneumonia doubles the probability of Mycoplasma pneumoniae.[66]

Diagnosis in adults

In general, in adults, investigations are not needed in mild cases.[67] There is a very low risk of pneumonia if all vital signs and auscultation are normal.[68] C-reactive protein (CRP) may help support the diagnosis.[69] For those with CRP less than 20 mg/L without convincing evidence of pneumonia, antibiotics are not recommended.[40]

Procalcitonin may help determine the cause and support decisions about who should receive antibiotics.[70] Antibiotics are encouraged if the 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.[40] In people requiring hospitalization, pulse oximetry, chest radiography and blood tests - including a complete blood count, serum electrolytes, C-reactive protein level, and possibly liver function tests - are recommended.[67]

The diagnosis of influenza-like illness can be made based on the signs and symptoms; however, confirmation of an influenza infection requires testing.[71] Thus, treatment is frequently based on the presence of influenza in the community or a rapid influenza test.[71]

Adults 65 years old or older, as well as cigarette smokers and people with ongoing medical conditions are at increased risk for pneumonia.[72]

Physical exam

Physical examination may sometimes reveal low blood pressure, high heart rate, or low oxygen saturation.[24] The respiratory rate may be faster than normal, and this may occur a day or two before other signs.[24][28] Examination of the chest may be normal, but it may show decreased expansion on the affected side. Harsh breath sounds from the larger airways that are transmitted through the inflamed lung are termed bronchial breathing and are heard on auscultation with a stethoscope.[24] Crackles (rales) may be heard over the affected area during inspiration.[24] Percussion may be dulled over the affected lung, and increased, rather than decreased, vocal resonance distinguishes pneumonia from a pleural effusion.[9]

Imaging

A chest X-ray showing a very prominent wedge-shaped area of airspace consolidation in the right lung characteristic of acute bacterial lobar pneumonia

CT of the chest demonstrating right-sided pneumonia (left side of the image)

A chest radiograph is frequently used in diagnosis.[23] 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.[23][67] If a person is sufficiently sick to require hospitalization, a chest radiograph is recommended.[67] Findings do not always match the severity of disease and do not reliably separate between bacterial and viral infection.[23]

X-ray presentations of pneumonia may be classified as lobar pneumonia, bronchopneumonia, lobular pneumonia, and interstitial pneumonia.[73] Bacterial, community-acquired pneumonia classically show lung consolidation of one lung segmental lobe, which is known as lobar pneumonia.[41] However, findings may vary, and other patterns are common in other types of pneumonia.[41] Aspiration pneumonia may present with bilateral opacities primarily in the bases of the lungs and on the right side.[41] Radiographs of viral pneumonia may appear normal, appear hyper-inflated, have bilateral patchy areas, or present similar to bacterial pneumonia with lobar consolidation.[41] Radiologic findings may not be present in the early stages of the disease, especially in the presence of dehydration, or may be difficult to interpret in the obese or those with a history of lung disease.[24] Complications such as pleural effusion may also be found on chest radiographs. Laterolateral chest radiographs can increase the diagnostic accuracy of lung consolidation and pleural effusion.[40]

A CT scan can give additional information in indeterminate cases[41] and provide more details in those with an unclear chest radiograph (for example occult pneumonia in chronic obstructive pulmonary disease). They can be used to exclude pulmonary embolism and fungal pneumonia, and detect lung abscesses in those who are not responding to treatments.[40] However, CT scans are more expensive, have a higher dose of radiation, and cannot be done at bedside.[40]

Lung ultrasound may also be useful in helping to make the diagnosis.[74] Ultrasound is radiation free and can be done at bedside. However, ultrasound requires specific skills to operate the machine and interpret the findings.[40] It may be more accurate than chest X-ray.[75]

Pneumonia seen by ultrasound[76]

Pneumonia seen by ultrasound[76]

Pneumonia seen by ultrasound[76]

Right middle lobe pneumonia in a child as seen on plain X-ray

Microbiology

In people managed in the community, determining the causative agent is not cost-effective and typically does not alter management.[23] For people who do not respond to treatment, sputum culture should be considered, and culture for Mycobacterium tuberculosis should be carried out in persons with a chronic productive cough.[67] Microbiological evaluation is also indicated in severe pneumonia, alcoholism, asplenia, immunosuppression, HIV infection, and those being empirically treated for MRSA of pseudomonas.[40][77] Although positive blood culture and pleural fluid 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 colonisation of respiratory tract.[40] Testing for other specific organisms may be recommended during outbreaks, for public health reasons.[67] In those hospitalized for severe disease, both sputum and blood cultures are recommended,[67] as well as testing the urine for antigens to Legionella and Streptococcus.[78] Viral infections, can be confirmed via detection of either the virus or its antigens with culture or polymerase chain reaction (PCR), among other techniques.[12] Mycoplasma, Legionella, Streptococcus, and Chlamydia can also be detected using PCR techniques on bronchoalveolar lavage and nasopharyngeal swab.[40] The causative agent is determined in only 15% of cases with routine microbiological tests.[9]

Classification

Pneumonitis refers to lung inflammation; pneumonia refers to pneumonitis, usually due to infection but sometimes non-infectious, that has the additional feature of pulmonary consolidation.[79] Pneumonia is most commonly classified by where or how it was acquired: community-acquired, aspiration, healthcare-associated, hospital-acquired, and ventilator-associated pneumonia.[41] It may also be classified by the area of the lung affected: lobar, bronchial pneumonia and acute interstitial pneumonia;[41] or by the causative organism.[80] Pneumonia in children may additionally be classified based on signs and symptoms as non-severe, severe, or very severe.[81]

The setting in which pneumonia develops is important to treatment,[82][83] as it correlates to which pathogens are likely suspects,[82] which mechanisms are likely, which antibiotics are likely to work or fail,[82] and which complications can be expected based on the person's health status.

Community

Community-acquired pneumonia (CAP) is acquired in the community,[82][83] outside of health care facilities. Compared with healthcare-associated pneumonia, it is less likely to involve multidrug-resistant bacteria. Although the latter are no longer rare in CAP,[82] they are still less likely. Prior stays in healthcare-related environments such as hospitals, nursing homes, or hemodialysis centers or a history of receiving domiciliary care can increase patients' risk for CAP caused by multidrug-resistant bacteria.[84]

Healthcare

Health care-associated pneumonia (HCAP) is an infection associated with recent exposure to the health care system,[82] including hospitals, outpatient clinics, nursing homes, dialysis centers, chemotherapy treatment, or home care.[83] HCAP is sometimes called MCAP (medical care-associated pneumonia).

People may become infected with pneumonia in a hospital; this is defined as pneumonia not present at the time of admission (symptoms must start at least 48 hours after admission).[83][82] It is likely to involve hospital-acquired infections, with higher risk of multidrug-resistant pathogens. People in a hospital often have other medical conditions, which may make them more susceptible to pathogens in the hospital.

Ventilator-associated pneumonia occurs in people breathing with the help of mechanical ventilation.[82][33] Ventilator-associated pneumonia is specifically defined as pneumonia that arises more than 48 to 72 hours after endotracheal intubation.[83]

Differential diagnosis

Several diseases can present with similar signs and symptoms to pneumonia, such as: chronic obstructive pulmonary disease, asthma, pulmonary edema, bronchiectasis, lung cancer, and pulmonary emboli.[9] Unlike pneumonia, asthma and COPD typically present with wheezing, pulmonary edema presents with an abnormal electrocardiogram, cancer and bronchiectasis present with a cough of longer duration, and pulmonary emboli present with acute onset sharp chest pain and shortness of breath.[9] Mild pneumonia should be differentiated from upper respiratory tract infection (URTI). Severe pneumonia should be differentiated from acute heart failure. Pulmonary infiltrates that resolved after giving mechanical ventilation should point to heart failure and atelectasis rather than pneumonia. For recurrent pneumonia, underlying lung cancer, metastasis, tuberculosis, a foreign bodies, immunosuppression, and hypersensitivity should be suspected.[40]

Deaths from lower respiratory infections per million persons in 2012

Disability-adjusted life year for lower respiratory infections per 100,000 inhabitants in 2004[141]

Pneumonia is a common illness affecting approximately 450 million people a year and occurring in all parts of the world.[12] It is a major cause of death among all age groups resulting in 4 million deaths (7% of the world's total death) yearly.[12][13] Rates are greatest in children less than five, and adults older than 75 years.[12] It occurs about five times more frequently in the developing world than in the developed world.[12] Viral pneumonia accounts for about 200 million cases.[12] In the United States, as of 2009, pneumonia is the 8th leading cause of death.[24]

Children

In 2008, pneumonia occurred in approximately 156 million children (151 million in the developing world and 5 million in the developed world).[12] 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.[12][23][142] Countries with the greatest burden of disease include India (43 million), China (21 million) and Pakistan (10 million).[143] It is the leading cause of death among children in low income countries.[12][13] 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.[144] Approximately half of these deaths can be prevented, as they are caused by the bacteria for which an effective vaccine is available.[145] The IDSA has recommended that children and infants with symptoms of CAP should be hospitalized so they have access to pediatric nursing care.[146] 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.[147]

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Pneumonia is an inflammatory condition of the lung primarily affecting the small air sacs known as alveoli.[3] [14] Symptoms typically include some combination of productive or dry cough, chest pain, fever, and difficulty breathing.[15] The severity of the condition is variable.[15] Pneumonia Other names Pneumonitis Chest X-ray of a pneumonia