pneumonia pneumonia pneumonia is an inflammatory condition of the lung primarily affecting the small air sacs known as alveoli. symptoms typically include some combination of productive or dry cough, chest pain, fever, and difficulty breathing. the severity of the condition is variable. not to be confused with pneumonitis. pneumoniaother namespneumonitischest x-ray of a pneumonia caused by influenza and haemophilus influenzae, with patchy consolidations, mainly in the right upper lobe (arrow)pronunciation/njuːˈmoʊniə/ new-mohn-ee-ə specialtypulmonology, infectious diseasesymptomscough, shortness of breath, chest pain, feverdurationfew weekscausesbacteria, virus, aspirationrisk factorscystic fibrosis, copd, sickle cell disease, asthma, diabetes, heart failure, history of smoking, very young age, older agediagnostic methodbased on symptoms, chest x-raydifferential diagnosiscopd, asthma, pulmonary edema, pulmonary embolismpreventionvaccines, handwashing, not smokingmedicationantibiotics, antivirals, oxygen therapyfrequency450 million (7%) per yeardeathsfour million per year pneumonia is usually caused by infection with viruses or bacteria, and less commonly by other microorganisms. identifying the responsible pathogen can be difficult. diagnosis is often based on symptoms and physical examination. chest x-rays, blood tests, and culture of the sputum may help confirm the diagnosis. the disease may be classified by where it was acquired, such as community- or hospital-acquired or healthcare-associated pneumonia. 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. 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. other methods of prevention include hand washing to prevent infection, not smoking, and social distancing. treatment depends on the underlying cause. pneumonia believed to be due to bacteria is treated with antibiotics. if the pneumonia is severe, the affected person is generally hospitalized. oxygen therapy may be used if oxygen levels are low. each year, pneumonia affects about 450 million people globally (7% of the population) and results in about 4 million deaths. with the introduction of antibiotics and vaccines in the 20th century, survival has greatly improved. nevertheless, pneumonia remains a leading cause of death in developing countries, and also among the very old, the very young, and the chronically ill. pneumonia often shortens the period of suffering among those already close to death and has thus been called "the old man's friend". signs and symptoms symptoms frequency symptomfrequency cough79–91% fatigue90% fever71–75% shortness of breath67–75% sputum60–65% chest pain39–49% 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. 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, malnutrition 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 blue-tinged skin, unwillingness to drink, convulsions, ongoing vomiting, extremes of temperature, or a decreased level of consciousness. 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 legionella may occur with abdominal pain, diarrhea, or confusion. pneumonia caused by streptococcus pneumoniae is associated with rusty colored sputum. pneumonia caused by klebsiella may have bloody sputum often described as "currant jelly". bloody sputum (known as hemoptysis) may also occur with tuberculosis, gram-negative pneumonia, lung abscesses and more commonly acute bronchitis. 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. viral pneumonia presents more commonly with wheezing 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 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. a causative agent may not be isolated in about half of cases despite careful testing. 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. most patients (62%) had no detectable pathogens in their sample, and unexpectedly, respiratory viruses were detected more frequently than bacteria. 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%)." 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. 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. additional risks in children include not being breastfed, exposure to cigarette smoke and other air pollution, malnutrition, and poverty. the use of acid-suppressing medications – such as proton-pump inhibitors or h2 blockers – is associated with an increased risk of pneumonia. approximately 10% of people who require mechanical ventilation develop ventilator-associated pneumonia, and people with a gastric feeding tube have an increased risk of developing aspiration pneumonia. moreover, the misplacement of a feeding tube can lead to aspiration pneumonia. 28% of tube malposition results in pneumonia. 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. 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. bacteria main article: bacterial pneumonia 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. other commonly isolated bacteria include haemophilus influenzae in 20%, chlamydophila pneumoniae in 13%, and mycoplasma pneumoniae in 3% of cases; staphylococcus aureus; moraxella catarrhalis; and legionella pneumophila. 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). the spreading of organisms is facilitated by certain risk factors. 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. streptococcus pneumoniae is more common in the winter, and it should be suspected in persons aspirating a large number of anaerobic organisms. viruses main article: viral pneumonia a chest x-ray of a patient with severe viral pneumonia due to sars in adults, viruses account for about one third of pneumonia cases, and in children for about 15% of them. commonly implicated agents include rhinoviruses, coronaviruses, influenza virus, respiratory syncytial virus (rsv), adenovirus, and parainfluenza. herpes simplex virus rarely causes pneumonia, except in groups such as newborns, persons with cancer, transplant recipients, and people with significant burns. after organ transplantation or in otherwise immunocompromised persons, there are high rates of cytomegalovirus 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 times of the year; during flu season, for example, influenza may account for more than half of all viral cases. outbreaks of other viruses also occur occasionally, including hantaviruses and coronaviruses. severe acute respiratory syndrome coronavirus 2 (sars-cov-2) can also result in pneumonia. fungi main article: fungal pneumonia fungal pneumonia is uncommon, but occurs more commonly in individuals with weakened immune systems due to aids, immunosuppressive drugs, or other medical problems. 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. 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. for people infected with hiv/aids, pcp is a common opportunistic infection. parasites main article: parasitic pneumonia a variety of parasites can affect the lungs, including toxoplasma gondii, strongyloides stercoralis, ascaris lumbricoides, and plasmodium malariae. these organisms typically enter the body through direct contact with the skin, ingestion, or via an insect vector. except for paragonimus westermani, most parasites do not specifically affect 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 eosinophilic reaction, which may result in eosinophilic pneumonia. in other infections, such as malaria, lung involvement is due primarily to cytokine-induced systemic inflammation. in the developed world, these infections are most common in people returning from travel or in immigrants. around the world, parasitic pneumonia is most common in the immunodeficient. noninfectious main article: idiopathic interstitial pneumonia idiopathic interstitial pneumonia or noninfectious pneumonia 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. lipoid pneumonia is another rare cause due to lipids entering the lung. these lipids can either be inhaled or spread to the lungs from elsewhere in the body. mechanisms pneumonia fills the lung's alveoli with fluid, hindering oxygenation. the alveolus on the left is normal, whereas the one on the right is full of fluid from pneumonia. pneumonia frequently starts as an upper respiratory tract infection that moves into the lower respiratory tract. it is a type of pneumonitis (lung inflammation). the normal flora of the upper airway give protection by competing with pathogens for nutrients. in the lower airways, reflexes of the glottis, actions of complement proteins and immunoglobulins are important for protection. microaspiration of contaminated secretions can infect the lower airways and cause pneumonia. the progress of pneumonia is determined by the virulence of the organism; the amount of organism required to start an infection; and the body's immune response against the infection. bacterial most bacteria enter the lungs via small aspirations of organisms residing in the throat or nose. half of normal people have these small aspirations during sleep. while the throat always contains bacteria, potentially infectious ones reside there only at certain times and under certain conditions. a minority of types of bacteria such as mycobacterium tuberculosis and legionella pneumophila reach the lungs via contaminated airborne droplets. bacteria can also spread via the blood. once in the lungs, bacteria may invade the spaces between cells and between alveoli, where the macrophages and neutrophils (defensive white blood cells) attempt to inactivate the bacteria. the neutrophils also release cytokines, 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 touch their eyes or nose. other viral infections occur