Community-acquired pneumonia: Difference between revisions

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[[Image:Pneumonia.gif|thumb|right|200px|'''Pneumonia.''' Chest x-ray showing increased shadowing in right lung (left side of image). <small>(''Source: Center for Disease Control and Prevention''.)</small>]]

{{Infobox medical condition (new)

'''Community-acquired pneumonia''' ('''CAP''') is a [[disease]] in which individuals who are have not recently been [[hospital]]ized develop an [[infection]] of the [[lung]]s (pneumonia). CAP is a common illness and can affect people of all ages. CAP often causes problems [[breathing]], [[fever]], chest [[pain]]s, and a [[cough]]. CAP occurs because the areas of the lung which absorb [[oxygen]] ([[alveoli]]) from the [[atmosphere]] become filled with fluid and cannot work effectively.

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'''Community-acquired pneumonia''' (CAP) refers to [[pneumonia]] contracted by a person outside of the healthcare system. In contrast, [[hospital-acquired pneumonia]] (HAP) is seen in patients who are in a hospital or who have recently been hospitalized in the last 48 hours. Those who live in long-term care facilities or who had pneumonia after 48 hours of hospitalization for another cause are also classified as having CAP (they were previously designated as having HCAP (healthcare associated pneumonia)).<ref name="Vaughn 2024" /> CAP is common, affecting people of all ages, and its symptoms occur as a result of oxygen-absorbing areas of the lung ([[Pulmonary alveolus|alveoli]]) becoming colonized by a pathogenic microorganism (such as bacteria, viruses or fungi). The resulting inflammation and tissue damage causes fluid to fill the alveoli, inhibiting lung function and causing the symptoms of the disease.<ref name="Vaughn 2024" /> Common symptoms of CAP include [[dyspnea]], [[fever]], [[chest pain]]s and [[cough]].

10% of those with CAP are hospitalized. The 30 day mortality for those hospitalized with CAP is 2.8% for adults younger than 60 and 26.8% for adults older than 60 with other medical conditions.<ref name="Vaughn 2024" />

CAP occurs throughout the world and is a leading cause of illness and death. Causes of CAP include [[bacteria]], [[viruses]], [[fungi]], and [[parasites]]. CAP can be [[diagnosis|diagnosed]] by [[symptom]]s and [[physical examination]] alone, though [[x-ray]]s, examination of the [[sputum]], and other tests are often used. Individuals with CAP sometimes require [[treatment]] in a [[hospital]]. CAP is primarily treated with [[antibiotic]] [[medication]]. Some forms of CAP can be [[Preventive medicine|prevented]] by [[vaccination]].{{an|Sharma}}

CAP, the most common type of pneumonia, is a leading [[List of causes of death by rate|cause of illness and death]] worldwide{{Citation needed|date=May 2020}}. Its causes include [[bacteria]], [[virus]]es, [[Fungus|fungi]] and [[parasitism|parasites]].<ref>{{Cite web|title = Pneumonia Causes – Mayo Clinic|url = http://www.mayoclinic.org/diseases-conditions/pneumonia/basics/causes/con-20020032|website = www.mayoclinic.org|access-date = 2015-05-18}}</ref> CAP is diagnosed by assessing symptoms, performing a physical examination, by [[x-ray]] or by [[sputum]] examination. Some form of chest imaging, usually in the form of a chest x-ray, showing characteristic findings is required for the diagnosis.<ref name="Vaughn 2024" /> Most cases can be treated on an outpatient basis, but some patients with CAP require hospitalization. CAP is treated primarily with [[antibiotics]], antivirals or antifungals depending on the confirmed or suspected microorganism pathogen.<ref>{{Cite web|title = Pneumonia Treatments and drugs – Mayo Clinic|url = http://www.mayoclinic.org/diseases-conditions/pneumonia/basics/treatment/con-20020032|website = www.mayoclinic.org|access-date = 2015-05-18}}</ref> Some forms of CAP can be prevented by [[vaccination]]<ref>{{Cite journal |doi = 10.1097/MCP.0000000000000369|pmid = 28198725|title = Adult pneumococcal vaccination|journal = Current Opinion in Pulmonary Medicine|volume = 23|issue = 3|pages = 225–230|year = 2017|last1 = José|first1 = Ricardo J.|last2 = Brown|first2 = Jeremy S.| s2cid=4700975 }}</ref> and by abstaining from tobacco products.<ref>{{Cite web|title = Pneumonia Prevention – Mayo Clinic|url = http://www.mayoclinic.org/diseases-conditions/pneumonia/basics/prevention/con-20020032|website = www.mayoclinic.org|access-date = 2015-05-18}}</ref> Vaccination against [[flu vaccine|influenza]], [[Covid vaccine|Covid]], [[RSV vaccine|respiratory syncytial virus]] and the [[pneumococcal conjugate vaccine]] can all prevent CAP.<ref name="Vaughn 2024" />

==Symptoms==

Symptoms of CAP commonly include [[dyspnea|problems breathing]]; coughing that produces greenish or yellow [[sputum]]; a high [[fever]] that may be accompanied with sweating, chills, and [[rigor (medicine)|uncontrollable shaking]]; sharp or stabbing [[chest pain]]; and rapid, shallow breathing that is often painful. Less commonly, there may be the coughing up of blood ([[hemoptysis]]), [[headache]]s (including migraine headaches), [[anorexia|loss of appetite]], excessive fatigue, blueness of the skin ([[cyanosis]]), [[nausea]], [[vomiting]], [[diarrhea]], joint pain ([[arthalgia]]) or muscle aches ([[myalgia]]). The manifestations of pneumonia, like those for many conditions, may not be typical in older people. They may instead experience new or worsening confusion, [[hypothermia]], or falls. Infants may be overly sleepy, develop yellowing of the skin ([[jaundice]]) or have difficulties feeding. {{an|Metaly}}

== Signs and symptoms ==

==Diagnosis==

Individuals with symptoms of CAP require further evaluation. [[Physical examination]] by a health provider may reveal fever, an increased [[respiratory rate]] ([[hyperventilation|tachypnea]]), low [[blood pressure]] ([[hypotension]]), a fast [[heart rate]] ([[tachycardia]]), and/or changes in the amount of oxygen in the [[blood]]. Feeling the way the chest expands ([[palpation]]) and tapping the chest wall ([[Percussion (medicine)|percussion]]) to identify dull areas which do not [[resonance|resonate]] can identify areas of the lung which are stiff and full of fluid (consolidated). Examination of the lungs with the aid of a [[stethoscope]] can reveal several things. A lack of normal breath sounds or the presence of crackling sounds ([[rales]]) when the lungs are listened to ([[auscultation|auscultated]]) can also indicate consolidation. Increased vibration of the chest when speaking (tactile fremitus) and increased volume of whispered speech during [[auscultation]] of the chest can also reveal consolidation. {{an|Metlay}}

==={{anchor|Symptoms of CAP}}Common symptoms===

[[X-ray]]s of the chest, examination of the [[blood]] and [[sputum]] for infectious [[microorganisms]], and [[Medical laboratory|blood tests]] are commonly used to diagnose individuals with suspected CAP based upon symptoms and physical examination. The use of each test depends on the severity of illness, local practices, and the concern for any [[complication]]s resulting from the infection.

[[File:Symptoms of pneumonia.svg|300px|center|alt=Illustration of pneumonia symptoms on a human body]]

* Coughing which produces greenish or yellow sputum

* A high fever, accompanied by sweating, chills and shivering

* Sharp, stabbing chest pains

* Rapid, shallow, often painful breathing

==={{anchor|Less common symptoms}}Less-common symptoms===

All patients with CAP should have the amount of oxygen in their blood monitored with a machine called a [[pulse oximeter|pulse oximetry]]. This helps determine how well the lungs are able to work despite infection. In some cases, analysis of [[arterial blood gas]] may be required to accurately determine the amount of oxygen in the blood. [[Complete blood count]] (CBC), a blood test, may reveal extra [[white blood cell]]s, indicating an infection. Chest x-rays and chest [[computed tomography]] (CT) can reveal areas of [[opacity]] (seen as white) which represent consolidation. A normal chest x-ray makes CAP less likely; however, CAP is sometimes not seen on x-rays because the disease is either in its initial stages or involves a part of the lung not easily seen by x-ray. In some cases, chest CT can reveal a CAP which is not present on chest x-ray. X-rays can often be misleading, as many other diseases can mimic CAP such as [[congestive heart failure|heart problems]] or other types of lung damage.{{an|Syrjala}}

* Coughing up blood ([[hemoptysis]])

* Headaches, including migraines

* [[Anorexia (symptom)|Loss of appetite]]

* Excessive fatigue

* Bluish skin ([[cyanosis]])

* [[Nausea]]

* [[Vomiting]]

* [[Diarrhea]]

* Joint pain ([[arthralgia]])

* Muscle aches ([[myalgia]])

* Rapid heartbeat

* Dizziness or lightheadedness

==={{anchor|Symptoms in older people}}In the elderly===

Several tests can be performed to identify the cause of an individual's CAP. [[Blood culture]]s can be drawn to isolate any bacteria or fungi in the blood stream. Sputum [[Gram's stain]] and culture can also reveal the causative microorganism. In more severe cases, a procedure wherein a flexible scope is passed through the mouth into the lungs ([[bronchoscopy]]) can be used collect fluid for culture. Special tests can be performed if an uncommon microorganism is suspected (such as testing the urine for [[Legionella]] [[antigen]] when [[Legionellosis|Legionnaires' disease]] is a concern).

* New or worsening confusion

* [[Hypothermia]]

* Poor coordination, which may lead to falls

==={{anchor|Symptoms for infants}}In infants===

== Pathophysiology ==

* Unusual sleepiness

The symptoms of CAP are the result of both the invasion of the lungs by [[microorganism]]s and the [[immune system]]'s response to the infection. The mechanisms of infection are quite different for [[virus]]es and the other microorganisms.

* Yellowing of the skin ([[jaundice]])

* Difficulty feeding<ref name=Metaly />

=== {{anchor|Sepsis|Respiratory failure|Pleural effusion and empyema|Abscess}}Complications ===

Major complications of CAP include:

* [[Sepsis]] - A life-threatening reaction to infection. A common cause of sepsis is [[bacterial pneumonia]], frequently the result of infection with ''streptococcus pneumoniae''. Patients with sepsis require intensive care with blood pressure monitoring and support against hypotension. Sepsis can cause liver, kidney and heart damage.

* Respiratory failure - CAP patients often have [[dyspnea]], which may require support. Non-invasive machines (such as [[bilevel positive airway pressure]]), a [[tracheal tube]] or a [[Medical ventilator|ventilator]] may be used.

* Pleural effusion and empyema - Microorganisms from the lung may trigger fluid collection in the [[pleural cavity]], or [[empyema]]. Pleural fluid, if present, should be [[thoracentesis|collected with a needle]] and examined. Depending on the results, complete drainage of the fluid with a [[chest tube]] may be necessary to prevent proliferation of the infection. Antibiotics, which do not penetrate the pleural cavity well, are less effective.

* [[Abscess]] - A pocket of fluid and bacteria may appear on X-ray as a cavity in the lung. Abscesses, typical of [[aspiration pneumonia]], usually contain a mixture of [[Anaerobic organism|anaerobic bacteria]]. Although antibiotics can usually cure abscesses, sometimes they require drainage by a surgeon or [[Interventional radiology|radiologist]].

== {{anchor|Cause}}Causes ==

*''Viruses''

Many different microorganisms can cause CAP. However, the most common cause is ''[[Streptococcus pneumoniae]]''. Certain groups of people are more susceptible to CAP-causing pathogens - [[infant]]s, adults with [[chronic condition]]s (such as [[chronic obstructive pulmonary disease]]), and senior citizens. [[Alcoholism|Alcoholics]] and others with compromised immune systems are more likely to develop CAP from ''[[Haemophilus influenzae]]'' or ''[[Pneumocystis jirovecii]]''.<ref>{{Cite web|title = What is pneumonia? What causes pneumonia?|url = http://www.medicalnewstoday.com/articles/151632.php|access-date = 2015-05-18}}</ref> A definitive cause is identified in only half the cases.{{cn|date=March 2022}}

:Viruses must invade cells in order to reproduce. Typically, a virus will reach the lungs by traveling in droplets through the [[mouth]] and [[nose]] with [[inhalation]]. There, the virus invades the cells lining the airways and the alveoli. This invasion often leads cell death either through direct killing by the virus or by self-destruction through [[apoptosis]]. Further damage to the lungs occurs when the immune system responds to the infection. [[White blood cell]]s, in particular [[lymphocyte]]s, are responsible for activating a variety of chemicals ([[cytokine]]s) which cause leaking of fluid into the alveoli. The combination of cellular destruction and fluid-filled alveoli interrupts the transportation of oxygen into the bloodstream. In addition to the effects on the lungs, many viruses affect other [[organ]]s and can lead to illness affecting many different bodily functions. Viruses also make the body more susceptible to bacterial infection; for this reason, bacterial pneumonia often complicates viral CAP.

=== Neonates and infants ===

*''Bacteria and fungi''

It is possible for a fetus to develop a lung infection before birth by aspirating infected [[amniotic fluid]] or through a blood-borne infection which crossed the [[placenta]]. Infants can also inhale contaminated fluid from the vagina at birth. The most prevalent pathogen causing CAP in newborns is ''[[Streptococcus agalactiae]]'', also known as group-B streptococcus (GBS). GBS causes more than half of CAP in the first week after birth.<ref name=Webber /> Other bacterial causes of neonatal CAP include ''[[Listeria monocytogenes]]'' and a variety of [[Mycobacterium|mycobacteria]]. CAP-causing viruses may also be transferred from mother to child; [[herpes simplex virus]], the most common, is life-threatening, and [[adenoviridae]], [[mumps]] and [[enterovirus]] can also cause pneumonia. Another cause of neonatal CAP is ''[[Chlamydia trachomatis]]'', which, though acquired at birth, does not cause pneumonia until two to four weeks later. It usually presents with no fever and a characteristic, staccato cough.

:Bacteria and fungi also typically enter the lung with inhalation, though they can reach the lung through the bloodstream if other parts of the body are infected. Often, bacteria live in parts of the [[upper respiratory tract]] and are constantly being inhaled into the alveoli. Once inside the alveoli, [[bacteria]] and [[fungus|fungi]] travel into the spaces between the cells and also between adjacent alveoli through connecting pores. This invasion triggers the [[immune system]] to respond by sending white blood cells responsible for attacking microorganisms ([[neutrophil]]s) to the lungs. The neutrophils [[phagocytosis|engulf]] and kill the offending organisms but also release cytokines which result in a general activation of the immune system. This results in the fever, chills, and fatigue common in CAP. The neutrophils, bacteria, and fluid leaked from surrounding blood vessels fill the alveoli and result in impaired oxygen transportation. Bacteria often travel from the lung into the blood stream and can result in serious illness such as [[septic shock]], in which there is low blood pressure leading to damage in multiple parts of the body including the [[brain]], [[kidney]], and [[heart]].

CAP in older infants reflects increased exposure to microorganisms, with common bacterial causes including ''Streptococcus pneumoniae'', ''[[Escherichia coli]]'', ''[[Klebsiella pneumoniae]]'', ''[[Moraxella catarrhalis]]'' and ''[[Staphylococcus aureus]]''. Maternally-derived [[syphilis]] is also a cause of CAP in infants. Viral causes include [[human respiratory syncytial virus]] (RSV), [[human metapneumovirus]], adenovirus, [[human parainfluenza viruses]], [[influenza]] and [[rhinovirus]], and RSV is a common source of illness and hospitalization in infants.<ref name=Abzug /> CAP caused by fungi or parasites is not usually seen in otherwise-healthy infants.

*''Parasites''

:There are a variety of parasites which can affect the lungs. In general, these parasites enter the body through the skin or by being swallowed. Once inside the body, these parasites travel to the lungs, most often through the blood. There, a similar combination of cellular destruction and immune response causes disruption of oxygen transportation.

=== Children ===

== Microorganisms causing CAP ==

Although children older than one month tend to be at risk for the same microorganisms as adults, children under five years of age are much less likely to have pneumonia caused by ''[[Mycoplasma pneumoniae]]'', ''[[Chlamydophila pneumoniae]]'' or ''[[Legionella|Legionella pneumophila]]'' than older children. In contrast, older children and teenagers are more likely to acquire ''Mycoplasma pneumoniae'' and ''Chlamydophila pneumoniae'' than adults.<ref name=Wubbel />

There are over a hundred microorganisms which can cause CAP. The most common types of microorganisms are different among different groups of people. Newborn [[infant]]s, [[children]], and [[adult]]s are at risk for different spectrums of disease causing microorganisms. In addition, adults with [[chronic]] illnesses, who live in certain parts of the world, who reside in [[nursing home]]s, who have recently been treated with [[antibiotic]]s, or who are [[alcoholism|alcoholics]] are at risk for unique infections. Even when aggressive measures are taken, a definite cause for pneumonia is only identified in half the cases.

=== ''Infants''Adults ===

A full spectrum of microorganisms is responsible for CAP in adults, and patients with certain [[risk factor]]s are more susceptible to infections by certain groups of microorganisms. Identifying people at risk for infection by these organisms aids in appropriate treatment.

Newborn infants can acquire lung infections prior to being born either by breathing infected [[amniotic fluid]] or by blood-borne infection across the [[placenta]]. Infants can also inhale ([[aspirate]] fluid from the [[birth]] canal as they are being born. The most important infection in newborns is caused by [[Streptococcus agalactiae]], also known as Group B Streptococcus or GBS. GBS causes at least 50% of cases of CAP in the first week of life.{{an|Webber}} Other bacterial causes in the newborn period include ''[[Listeria monocytogenes]]'' and [[tuberculosis]]. Viruses can also be transferred from mother to child; [[herpes simplex virus]] is the most common and life-threatening, but [[adenovirus]], [[mumps]], and [[enterovirus]] can also cause disease.

Many less-common organisms can cause CAP in adults; these may be determined by identifying specific risk factors, or when treatment for more common causes fails.

=== Risk factors ===

CAP in older infants reflects increased exposure to microorganisms. Common bacterial causes include ''[[Streptococcus pneumoniae]]'', ''[[Escherichia coli]]'', ''[[Klebsiella pneumoniae]]'', ''[[Moraxella catarrhalis]]'', and ''[[Staphylococcus aureus]]''. A unique cause of CAP in this group is ''[[Chlamydia trachomatis]]'', which is acquired during birth but which does not cause pneumonia until 2-4 weeks later. Common viruses include [[respiratory syncytial virus]] (RSV), [[metapneumovirus]], [[adenovirus]], [[parainfluenza]], [[influenza]], and [[rhinovirus]]. RSV in particular is a common source of illness and hospitalization.{{an|Abzug}} Fungi and parasites are not typically encountered in otherwise healthy infants, though maternally-derived [[syphilis]] can be a cause of CAP in this age group.

Some patients have an underlying problem which increases their risk of infection. Some risk factors are:

* ''Obstruction'' - When part of the airway ([[bronchus]]) leading to the alveoli is obstructed, the lung cannot eliminate fluid; this can lead to pneumonia. One cause of obstruction, especially in young children, is inhalation of a foreign object such as a marble or toy. The object lodges in a small airway, and pneumonia develops in the obstructed area of the lung. Another cause of obstruction is [[lung cancer]], which can block the flow of air.

* ''Lung disease'' - Patients with underlying lung disease are more likely to develop pneumonia. Diseases such as emphysema and habits such as smoking result in more frequent and more severe bouts of pneumonia. In children, recurrent pneumonia may indicate [[cystic fibrosis]] or [[pulmonary sequestration]].

* ''Immune problems'' - [[Immunodeficiency|Immune-deficient]] patients, such as those with [[HIV/AIDS]], are more likely to develop pneumonia. Other immune problems that increase the risk of developing pneumonia range from severe childhood immune deficiencies, such as [[Wiskott–Aldrich syndrome]], to the less severe [[common variable immunodeficiency]].<ref name=Mundy />

=== ''Children''Pathophysiology ===

The symptoms of CAP are the result of lung infection by microorganisms and the response of the [[immune system]] to the infection. Mechanisms of infection are different for viruses and other microorganisms.{{cn|date=March 2022}}

For the most part, children older than one month of life are at risk for the same microorganisms as adults. However, children less than five years are much less likely to have pneumonia caused by ''[[Mycoplasma pneumoniae]]'', ''[[Chlamydophila pneumoniae]]'', or ''[[Legionella|Legionella pneumophila]]''. In contrast, older children and teenagers are more likely to acquire ''[[Mycoplasma pneumoniae]]'' and ''[[Chlamydophila pneumoniae]]'' than adults.{{an|Wubbel}}

=== ''Adults'' Viruses===

Up to 20 percent of CAP cases can be attributed to viruses.<ref>{{Cite book|title=Respiratory infections|last=Mandell|first=L|publisher=CRC Press|year=2006|pages=338}}</ref> The most common viral causes are influenza, parainfluenza, human respiratory syncytial virus, human metapneumovirus and adenovirus. Less common viruses which may cause serious illness include [[chickenpox]], [[Severe acute respiratory syndrome|SARS]], [[Influenza A virus subtype H5N1|avian flu]] and [[hantavirus]].<ref name="Roux" />

The full spectrum of microorganisms are responsible for CAP in adults. Several important groups of organisms are more common among people with certain [[risk factor]]s. Identifying people at risk for these organisms is important for appropriate treatment.

Typically, a virus enters the lungs through the inhalation of water droplets and invades the cells lining the airways and the alveoli. This leads to cell death; the cells are killed by the virus or they [[apoptosis|self-destruct]]. Further lung damage occurs when the immune system responds to the infection. [[White blood cell]]s, particularly [[lymphocyte]]s, activate chemicals known as [[cytokine]]s which cause fluid to leak into the alveoli. The combination of cell destruction and fluid-filled alveoli interrupts the transportation of oxygen into the bloodstream. In addition to their effects on the lungs, many viruses affect other organs. Viral infections weaken the immune system, making the body more susceptible to bacterial infection, including bacterial pneumonia.

*''Viruses''

:Viruses cause 20% of CAP cases. The most common viruses are [[influenza]], [[parainfluenza]], [[respiratory syncytial virus]], [[metapneumovirus]], and [[adenovirus]]. Less common viruses causing significant illness include [[varicella|chicken pox]], [[SARS]], [[H5N1|avian flu]], and [[hantavirus]].{{an|Roux}}

===Bacteria and fungi===

*''Atypical organisms''

:TheAlthough most common bacterial causescases of bacterial pneumonia are thecaused so-calledby ''Streptococcus pneumoniae'', infections by [[atypical bacteria]] such as ''[[Mycoplasma pneumoniae]],'' and ''[[Chlamydophila pneumoniae]].,'' and ''[[Legionella|Legionella pneumophila]]'' iscan consideredalso atypicalcause butCAP. isEnteric less[[gram-negative common.bacteria]], Atypicalsuch organismsas are''[[Escherichia morecoli]]'' difficultand to''[[Klebsiella growpneumoniae]]'', respondare toa differentgroup antibiotics,of andbacteria werethat discoveredtypically morelive recently thanin the typical[[large intestine]]; contamination of food and water by these bacteria discoveredcan result in theoutbreaks earlyof pneumonia. ''[[twentiethPseudomonas centuryaeruginosa]]'', an uncommon cause of CAP, is a difficult bacteria to treat.

Bacteria and fungi typically enter the lungs by inhalation of water droplets, although they can reach the lung through the bloodstream if an infection is present. In the alveoli, bacteria and fungi travel into the spaces between cells and adjacent alveoli through connecting pores. The immune system responds by releasing [[neutrophil granulocyte]]s, white blood cells responsible for attacking microorganisms, into the lungs. The neutrophils [[phagocytosis|engulf]] and kill the microorganisms, releasing cytokines which activate the entire immune system. This response causes fever, chills and fatigue, common symptoms of CAP. The neutrophils, bacteria and fluids leaked from surrounding blood vessels fill the alveoli, impairing oxygen transport. Bacteria may travel from the lung to the bloodstream, causing [[septic shock]] (very low blood pressure which damages the brain, kidney, and heart).

*''Streptococcus pneumoniae''

:''[[Streptococcus pneumoniae]]'' is a common bacterial cause of CAP. Prior to the development of antibiotics and vaccination, it was a leading cause of death. Traditionally highly sensitive to [[penicillin]], during the [[1970s]] resistance to multiple antibiotics began to develop. Current strains of "drug resistant Streptococcus pneumoniae" or DRSP are common, accounting for twenty percent of all Streptococcus pneumoniae infections. Adults with risk factors for DRSP including being older than 65, having exposure to children in [[day care]], having alcoholism or other severe underlying disease, or recent treatment with antibiotics should initially be treated with antibiotics effective against DRSP. {{an|Ruhe}}

===Parasites===

*''Hemophilus influenzae''

A variety of parasites can affect the lungs, generally entering the body through the skin or by being swallowed. They then travel to the lungs through the blood, where the combination of cell destruction and immune response disrupts oxygen transport.

:''[[Haemophilus influenzae|Hemophilus influenzae]]'' is another common bacterial cause of CAP. First discovered in [[1892]], it was initially believed to be the cause of influenza because it commonly causes CAP in people who have suffered recent lung damage from viral pneumonia.

== Diagnosis ==

*''Enteric Gram negative bacteria''

Patients with symptoms of CAP require evaluation. Diagnosis of pneumonia is made clinically, rather than on the basis of a particular test.<ref name="Mandell">{{cite journal | last1=Mandell | first1=L. A. | last2=Wunderink | first2=R. G. | last3=Anzueto | first3=A. | last4=Bartlett | first4=J. G. | last5=Campbell | first5=G. D. | last6=Dean | first6=N. C. | last7=Dowell | first7=S. F. | last8=File | first8=T. M. | last9=Musher | first9=D. M. | last10=Niederman | first10=M. S. | last11=Torres | first11=A. | last12=Whitney | first12=C. G. | title=Infectious Diseases Society of America/American Thoracic Society Consensus Guidelines on the Management of Community-Acquired Pneumonia in Adults | journal=Clinical Infectious Diseases | publisher=Oxford University Press (OUP) | volume=44 | issue=Supplement 2 | date=2007-03-01 | issn=1058-4838 | pmc=7107997| doi=10.1086/511159 | pages=S27–S72 | pmid=17278083| doi-access=free }}</ref> Evaluation begins with a physical examination by a health provider, which may reveal fever, an increased [[respiratory rate]] ([[hyperventilation|tachypnea]]), low blood pressure ([[hypotension]]), a fast heart rate ([[tachycardia]]) and changes in the amount of oxygen in the blood. [[Palpation|Palpating]] the chest as it expands and [[Percussion (medicine)|tapping]] the chest wall to identify dull, non-resonant areas can identify stiffness and fluid, signs of CAP. Listening to the lungs with a stethoscope ([[auscultation]]) can also reveal signs associated with CAP. A lack of normal breath sounds or the presence of [[crackles]] can indicate fluid consolidation. Increased vibration of the chest when speaking, known as tactile fremitus, and increased volume of whispered speech during auscultation can also indicate the presence of fluid.<ref name=Metlay />

:The enteric Gram negative bacteria such as ''[[Escherichia coli]]'' and ''[[Klebsiella pneumoniae]]'' are a group of bacteria that typically live in the human [[colon|intestines]]. Adults with risk factors for infection including residence in a [[nursing home]], serious [[heart]] and [[lung]] disease, and recent antibiotic use should initially be treated with antibiotics effective against Enteric Gram negative bacteria.

Several tests can identify the cause of CAP. [[Blood culture]]s can isolate bacteria or fungi in the bloodstream. Sputum [[Gram staining]] and culture can also reveal the causative microorganism. In severe cases, [[bronchoscopy]] can collect fluid for culture. Special tests, such as urinalysis, can be performed if an uncommon microorganism is suspected.

*''Pseudomonas aeruginosa''

:''[[Pseudomonas aeruginosa]]'' is an uncommon cause of CAP but is a particularly difficult bacteria to treat. Individuals who are malnourished, have a lung disease called [[bronchiectasis]], are on [[corticosteroids]], or have recently had strong antibiotics for a week or more should initially be treated with antibiotics effective against ''Pseudomonas aeruginosa''.{{an|Lieberman}}

Chest X-rays and [[X-ray computed tomography]] (CT) can reveal areas of [[Opacity (optics)|opacity]] (seen as white), indicating consolidation.<ref name="Mandell"/> CAP does not always appear on x-rays, sometimes because the disease is in its initial stages or involves a part of the lung not clearly visible on x-ray. In some cases, chest CT can reveal pneumonia not seen on x-rays. However, [[congestive heart failure]] or other types of lung damage can mimic CAP on x-ray.<ref name=Syrjala />

Many less common organisms cause CAP. They are typically identified because an individual has special risk factors or after treatment for the common causes has failed. These rarer causes are covered in more detail in their specific pages: [[bacterial pneumonia]], [[viral pneumonia]], [[fungal pneumonia]], and [[parasitic pneumonia]].

When signs of pneumonia are discovered during evaluation, chest X-rays and examination of the blood and sputum for infectious microorganisms may be done to support a diagnosis of CAP. The diagnostic tools employed will depend on the severity of illness, local practices and concern about [[Complication (medicine)|complications]] of the infection. All patients with CAP should have their blood oxygen monitored with [[pulse oximetry]]. In some cases, [[arterial blood gas]] analysis may be required to determine the amount of oxygen in the blood. A [[complete blood count]] (CBC) may reveal extra [[white blood cell]]s, indicating infection.{{cn|date=March 2022}}

== Treatment ==

CAP is treated by administering an antibiotic which is effective in killing the offending microorganism as well as managing any complications of the infection. If the causative microorganism is identified, different antibiotics are tested in the laboratory in order to identify which medication will be most effective. Often, however, no microorganism is ever identified. Also, since laboratory testing can take several days, there is some delay until an organism is identified. In both cases, a person's risk factors for different organisms must be remembered when choosing the initial antibiotics (called [[empiricism|empiric]] therapy). Additional consideration must be given to the setting in which the individual will be treated. Most people will be fully treated after taking oral pills while other people need to be hospitalized for [[intravenous]] antibiotics and, possibly, [[intensive care medicine|intensive care]]. In general, all therapies in older children and adults will include treatment for atypical bacteria. Typically this is a macrolide antibiotic such as [[azithromycin]] or [[clarithromycin]] although a [[fluoroquinolone]] such as [[levofloxacin]] can substitute.

=== ''NewbornPrevention infants'' ===

CAP may be prevented by treating underlying illnesses that increases its risk, by [[smoking cessation]], and by [[vaccination]]. Vaccination against ''[[Haemophilus influenzae]]'' and ''[[Streptococcus pneumoniae]]'' in the first year of life has been protective against childhood CAP. A vaccine against ''[[Streptococcus pneumoniae]]'', available for adults, is recommended for healthy individuals over 65 and all adults with COPD, [[heart failure]], [[diabetes mellitus]], [[cirrhosis]], [[alcoholism]], [[cerebrospinal fluid]] leaks or who have had a [[splenectomy]]. Re-vaccination may be required after five or ten years.<ref name=Butler />

Most newborn infants with CAP are hospitalized and given [[intravenous]] [[ampicillin]] and [[gentamicin]] for at least ten days. This treats the common bacteria ''[Streptococcus agalactiae]]'', ''[[Listeria monocytogenes]]'', and ''[[Escherichia coli]]''. If [[herpes simplex virus]] is the cause, intravenous [[acyclovir]] is administered for 21 days.

Patients who have been vaccinated against ''Streptococcus pneumoniae'', health professionals, nursing-home residents and pregnant women should be vaccinated annually against [[influenza]].<ref name=CDC /> During an outbreak, drugs such as [[amantadine]], [[rimantadine]], [[zanamivir]] and [[oseltamivir]] have been demonstrated to prevent influenza.<ref name=Hayden />

=== ''Children'' ===

Treatment of CAP in children depends on both the age of the child and the severity of his/her illness. Children less than five do not typically receive treatment to cover atypical bacteria. If a child does not need to be hospitalized, [[amoxicillin]] for seven days is a common treatment. However, with increasing prevalence of DRSP, other agents such as cefpodoxime will most likely become more popular in the future.{{an|Bradley}} Hospitalized children should receive intravenous [[ampicillin]], [[ceftriaxone]], or [[cefotaxime]].

=== ''Adults''Treatment ===

{{Multiple image|image1=Lungs with CAP Pretreatment.jpg|image2=Lungs with CAP postreatment.jpg|footer=Chest X-rays of a CAP patient before (''left'') and after treatment|footer_align=center}}

CAP is treated with an antibiotic that kills the infecting microorganism; treatment also aims at managing complications. If the causative microorganism is unidentified, which is often the case, the laboratory identifies the most effective antibiotic; this may take several days.

Health professionals consider a person's risk factors for various organisms when choosing an initial antibiotic. Additional consideration is given to the treatment setting; most patients are cured by oral medication, while others must be hospitalized for [[intravenous therapy]] or [[intensive care medicine|intensive care]].

In [[2001]], the American Thoracic Society, drawing on work by the British and Canadian Thoracic Societies, established guidelines for the management of adults with CAP which divided individuals with CAP into four categories based upon common organisms encountered.{{an|Neiderman}}

Current treatment guidelines recommend a beta-lactam, like amoxicillin, and a macrolide, like azithromycin or clarithromycin, or a [[Quinolone antibiotic|quinolone]], such as [[levofloxacin]]. [[Doxycycline]] is the antibiotic of choice in the UK for atypical bacteria, due to increased [[Clostridioides difficile infection]] in hospital patients linked to the increased use of [[clarithromycin]].

[[Ceftriaxone]] and [[azithromycin]] are often used to treat community-acquired pneumonia, which usually presents with a few days of cough, fever, and shortness of breath. Chest x-ray typically reveals a lobar infiltrate (rather than diffuse).<ref>{{Cite web|title=UWorld {{!}} Test Prep for NCLEX, SAT, ACT, MCAT, USMLE & More!|url=https://www.uworld.com/|access-date=2021-01-25|website=UWorld Test Prep}}</ref>

*''Healthy outpatients without risk factors''

:This group, the largest, is composed of otherwise healthy patients without risk factors for DRSP, enteric Gram negative bacteria, ''Pseudomonas'', or other less common causes of CAP. The primary microoganisms in this group are viruses, atypical bacteria, penicillin sensitive ''Streptococcus pneumoniae'', and ''Hemophilus influenzae''. Recommended management is with a macrolide antibiotic such as [[azithromycin]] or [[clarithromycin]] for seven to ten days.

=== Newborns ===

*''Outpatients with underlying illness and/or risk factors''

Most newborn infants with CAP are hospitalized, receiving IV [[ampicillin]] and [[gentamicin]] for at least ten days to treat the common causative agents ''[[Streptococcus agalactiae]]'', ''[[Listeria monocytogenes]]'' and ''[[Escherichia coli]]''. To treat the [[herpes simplex virus]], IV [[acyclovir]] is administered for 21 days.

:This group does not require hospitalization; its members either have underlying health problems (such as [[emphysema]] or [[congestive heart failure]]) or is at risk for DRSP and/or enteric Gram negative bacteria. Treatment is with a [[fluoroquinolone]] active against ''Streptococcus pneumoniae'' such as [[levofloxacin]] or a [[beta-lactam antibiotic]] such as [[cefpodoxime]], [[cefuroxime]], [[amoxicillin]], or [[Co-amoxiclav|amoxicillin/clavulanate]] plus a macrolide antibiotic such as [[azithromycin]] or [[clarithromycin]] for seven to ten days.

=== Children ===

*''Hospitalized individuals not at risk for Pseudomonas''

Treatment of CAP in children depends on the child's age and the severity of illness. Children under five are not usually treated for atypical bacteria. If hospitalization is not required, a seven-day course of [[amoxicillin]] is often prescribed, with [[co-trimaxazole]] as an alternative when there is allergy to penicillins.<ref name="ReferenceA">{{cite journal|last1=Lodha|first1=R|last2=Kabra|first2=SK|last3=Pandey|first3=RM|title=Antibiotics for community-acquired pneumonia in children.|journal=The Cochrane Database of Systematic Reviews|date=4 June 2013|volume=2013|issue=6|pages=CD004874|pmid=23733365|doi=10.1002/14651858.CD004874.pub4|pmc=7017636}}</ref> Further studies are needed to confirm the efficacy of newer antibiotics.<ref name="ReferenceA"/> With the increase in [[Pneumococcal infection#Treatment|drug-resistant Streptococcus pneumoniae]], antibiotics such as [[cefpodoxime]] may become more popular.<ref name=Bradley /> Hospitalized children receive intravenous [[ampicillin]], [[ceftriaxone]] or [[cefotaxime]], and a recent study found that a three-day course of antibiotics seems sufficient for most mild-to-moderate CAP in children.<ref name=pmid18729535>{{cite journal |vauthors=Dimopoulos G, Matthaiou DK, Karageorgopoulos DE, Grammatikos AP, Athanassa Z, Falagas ME |title=Short- versus long-course antibacterial therapy for community-acquired pneumonia : a meta-analysis |journal=Drugs |volume=68 |issue=13 |pages=1841–54 |year=2008 |pmid=18729535 |doi=10.2165/00003495-200868130-00004|doi-access=free }}</ref>

:This group requires hospitalization and administration of intravenous antibiotics. Treatment is with either an intravenous [[fluoroquinolone]] active against ''Streptococcus pneumoniae'' such as [[levofloxacin]] or [[beta-lactam antibiotic]] such as cefotaxime, ceftriaxone, ampicillin/sulbactam, or high-dose ampicillin plus an intravenous macrolide antibiotic such as [[azithromycin]] or [[clarithromycin]] for seven to ten days.

=== Adults ===

*''Individuals requiring intensive care at risk for Pseudomonas''

In 2001 the [[American Thoracic Society]], drawing on the work of the [[British Thoracic Society|British]] and [[Canadian Thoracic Society|Canadian Thoracic Societies]], established guidelines for the management of adult CAP by dividing patients into four categories based on common organisms:<ref name=Neiderman />

:Individuals being treated in an intensive care unit with risk factors for infection with ''Pseudomonas aeruginosa'' require specific antibiotics targeting this difficult to eradicate bacteria. One possible regimen is an intravenous antipseudomonal beta-lactam such as [[cefepime]], [[imipenem]], [[meropenem]], or [[piperacillin|piperacillin/tazobactam]] plus an intravenous antipseudomonal fluoroquinolone such as [[levofloxacin]]. Another recommended regimen is an intravenous antipseudomonal beta-lactam such as cefepime, imipenem, meropenem, or piperacillin/ tazobactam plus an intravenous aminoglycoside such as [[gentamicin]] or [[tobramycin]] plus either an intravenous macrolide such azithromycin or an intravenous nonpseudomonal fluoroquinolone such as [[ciprofloxacin]].

* Healthy outpatients without risk factors: This group (the largest) is composed of otherwise-healthy patients without risk factors for DRSP, enteric [[gram-negative bacteria]], ''Pseudomonas'' or other, less common, causes of CAP. Primary microorganisms are viruses, atypical bacteria, penicillin-sensitive ''Streptococcus pneumoniae'' and ''[[Haemophilus influenzae]]''. Recommended drugs are macrolide antibiotics, such as [[azithromycin]] or [[clarithromycin]], for seven<ref name="pmid17765048">{{cite journal |vauthors=Li JZ, Winston LG, Moore DH, Bent S |title=Efficacy of short-course antibiotic regimens for community-acquired pneumonia: a meta-analysis |journal=The American Journal of Medicine |volume=120 |issue=9 |pages=783–90 |date=September 2007 |pmid=17765048 |doi=10.1016/j.amjmed.2007.04.023}}</ref> to ten days. A shorter course of these antibiotics has been investigated, however, there is not sufficient evidence to make recommendations.<ref>{{cite journal |last1=López-Alcalde |first1=Jesús |last2=Rodriguez-Barrientos |first2=Ricardo |last3=Redondo-Sánchez |first3=Jesús |last4=Muñoz-Gutiérrez |first4=Javier |last5=Molero García |first5=José María |last6=Rodríguez-Fernández |first6=Carmen |last7=Heras-Mosteiro |first7=Julio |last8=Marin-Cañada |first8=Jaime |last9=Casanova-Colominas |first9=Jose |last10=Azcoaga-Lorenzo |first10=Amaya |last11=Hernandez Santiago |first11=Virginia |last12=Gómez-García |first12=Manuel |title=Short-course versus long-course therapy of the same antibiotic for community-acquired pneumonia in adolescent and adult outpatients |journal=Cochrane Database of Systematic Reviews |date=6 September 2018 |volume=2018 |issue=9 |pages=CD009070 |doi=10.1002/14651858.CD009070.pub2|pmid=30188565 |pmc=6513237 |hdl=10023/18430 |hdl-access=free }}</ref>

* Outpatients with underlying illness or risk factors: Although this group does not require hospitalization, they have underlying health problems such as emphysema or heart failure or are at risk for DRSP or enteric gram-negative bacteria. They may be treated with a quinolone active against ''Streptococcus pneumoniae'' (such as [[levofloxacin]]) or a [[β-lactam antibiotic]] (such as [[cefpodoxime]], [[cefuroxime]], [[amoxicillin]] or [[amoxicillin/clavulanic acid]]) and a macrolide antibiotic, such as [[azithromycin]] or [[clarithromycin]], for seven to ten days.<ref>{{cite journal |vauthors=Vardakas KZ, Siempos II, Grammatikos A, Athanassa Z, Korbila IP, Falagas ME |title=Respiratory fluoroquinolones for the treatment of community-acquired pneumonia: a meta-analysis of randomized controlled trials |journal=CMAJ |volume=179 |issue=12 |pages=1269–77 |date=December 2008 |pmid=19047608 |pmc=2585120 |doi=10.1503/cmaj.080358}}</ref>

* Hospitalized patients without risk for ''Pseudomonas'': This group requires intravenous antibiotics, with a quinolone active against ''Streptococcus pneumoniae'' (such as [[levofloxacin]]), a β-lactam antibiotic (such as cefotaxime, ceftriaxone, [[ampicillin/sulbactam]] or high-dose ampicillin plus a macrolide antibiotic (such as [[azithromycin]] or [[clarithromycin]]) for seven to ten days.

* Intensive-care patients at risk for ''[[Pseudomonas aeruginosa]]'': These patients require antibiotics targeting this difficult-to-eradicate bacterium. One regimen is an intravenous antipseudomonal beta-lactam such as [[cefepime]], [[imipenem]], [[meropenem]] or [[piperacillin|piperacillin/tazobactam]], plus an IV antipseudomonal fluoroquinolone such as [[levofloxacin]]. Another is an IV antipseudomonal beta-lactam such as cefepime, imipenem, meropenem or piperacillin/tazobactam, plus an aminoglycoside such as [[gentamicin]] or [[tobramycin]], plus a macrolide (such as azithromycin) or a nonpseudomonal fluoroquinolone such as [[ciprofloxacin]].

For mild-to-moderate CAP, shorter courses of antibiotics (3–7 days) seem to be sufficient.<ref name=pmid18729535/>

=== The decision to hospitalize ===

Some patients with CAP will be at increased risk of death despite antimicrobial treatment. A key reason for this is the host's exaggerated inflammatory response. There is a tension between controlling the infection on one hand and minimizing damage to other tissues on the other. Some recent research focuses on immunomodulatory therapy that can modulate the immune response in order to reduce injury to the lung and other affected organs such as the heart. Although the evidence for these agents has not resulted in their routine use, their potential benefits are promising.<ref>Woods DR, José RJ. Current and emerging evidence for immunomodulatory therapy in community-acquired pneumonia. Ann Res Hosp 2017;1:33 http://arh.amegroups.com/article/view/3806</ref>

== Prognosis ==

Individuals who are treated for CAP outside of the hospital have a mortality rate less than 1%. Fever typically responds in the first two days of therapy and other symptoms resolve in the first week. The x-ray, however, may remain abnormal for at least a month, even when CAP has been successfully treated. Among individuals who require hospitalization, the mortality rate averages 12% overall, but is as much as 40% in people who have bloodstream infections or require intensive care.{{an|Woodhead}}

=== {{anchor|Hospitalize}}Hospitalization ===

When CAP does not respond as expected, there are several possible causes. A complication of CAP may have occurred or a previously unknown health problem may be playing a role. Both situations are covered in more detail below. Additional causes include inappropriate antibiotics for the causative organism (ie DRSP), a previously unsuspected microorganism (such as [[tuberculosis]]), or a condition which mimics CAP (such as [[Wegener's granulomatosis]]). Additional testing may be performed and may include additional radiologic imaging (such as a [[Computed tomography|computed tomography scan]]) or a procedure such as a [[bronchoscopy]] or lung [[biopsy]].

Some CAP patients require intensive care, with [[clinical prediction rule]]s such as the [[pneumonia severity index]] and [[CURB-65]] guiding the decision whether or not to hospitalize.<ref name=Fine /> Factors increasing the need for hospitalization include:

* Age greater than 65

* Underlying chronic illnesses

* [[Respiratory rate]] greater than 30 per minute

* Systolic [[blood pressure]] less than 90 [[Millimeter of mercury|mmHg]]

* [[Heart rate]] greater than 125 per minute

* [[Temperature]] below 35 or over 40&nbsp;°C

* Confusion

* Evidence of infection outside the lung

Laboratory results indicating hospitalization include:

== Complications of CAP ==

* Arterial oxygen tension less than 60&nbsp;mm Hg

Despite appropriate antibiotic therapy, severe complications can result from CAP

* [[Carbon dioxide]] over 50 mmHg or [[pH]] under 7.35 while breathing room air

* [[Hematocrit]] under 30 percent

* [[Creatinine]] over 1.2&nbsp;mg/dl or [[blood urea nitrogen]] over 20&nbsp;mg/dl

* White-blood-cell count under 4 × 10^9/L or over 30 × 10^9/L

* Neutrophil count under 1 x 10^9/L

X-ray findings indicating hospitalization include:

=== ''Sepsis'' ===

* Involvement of more than one lobe of the [[lung]]

[[Sepsis]] can occur when microorganisms enter the blood stream and the [[immune system]] responds. Sepsis most often occurs with [[bacterial pneumonia]]; ''Streptococcus pneumoniae'' is the most common cause. Individuals with sepsis require hospitalization in an intensive care unit. They often require medications and intravenous fluids to keep their blood pressure from going too low. Sepsis can cause liver, kidney, and heart damage among other things.

* Presence of a cavity

* [[Pleural effusion]]

== Prognosis ==

=== ''Respiratory failure'' ===

The CAP outpatient mortality rate is less than one percent, with fever typically responding within the first two days of therapy, and other symptoms abating in the first week. However, X-rays may remain abnormal for at least a month. Hospitalized patients have an average mortality rate of 12 percent, with the rate rising to 40 percent for patients with bloodstream infections or those who require intensive care.<ref name=Woodhead /> Factors increasing mortality are identical to those indicating hospitalization.

Because CAP affects the lungs, often individuals with CAP have difficulty breathing. If enough of the lung is involved, it may not be possible for a person to breathe enough to live without support. Non-invasive machines such as a [[bilevel positive airway pressure]] machine may be used. Otherwise, placement of a [[endotracheal tube|breathing tube]] into the mouth may be necessary and a [[Medical ventilator|ventilator]] may be used to help the person breathe.

When CAP does not respond to treatment, this may indicate a previously unknown health problem, a treatment complication, inappropriate antibiotics for the causative organism, a previously unsuspected microorganism (such as [[tuberculosis]]) or a condition mimicking CAP (such as [[granuloma]] with polyangiitis). Additional tests include [[X-ray computed tomography]], [[bronchoscopy]] or lung [[biopsy]].

=== ''Pleural effusion and empyema'' ===

Occasionally, microorganisms from the lung will cause fluid to form in the space surrounding the lung, called the [[pleural cavity]]. If the microorganisms themselves are present, the fluid collection is often called an [[empyema]]. If pleural fluid is present in a person with CAP, the fluid should be collected with a needle ([[thoracentesis]]) and examined. Depending on the result of the examination, complete drainage of the fluid may be necessary, often with a [[chest tube]]. If the fluid is not drained, bacteria can continue to cause illness because antibiotics do not penetrate well into the pleural cavity.

=== ''Abcess'' ===

Occasionally, microorganisms in the lung will form a pocket of fluid and bacteria called an [[abcess]]. Abcesses can be seen on an x-ray as a cavity within the lung. Sometimes abcesses must be drained by a [[surgeon]] or [[Interventional radiology|radiologist]] because antibiotics often fail to kill microorganisms within an abcess.

== Special circumstances leading to CAP ==

== Epidemiology ==

CAP is a common illnessworldwide, in all parts of the world. Itand is a major cause of death amongin all age groups. In children, themost majoritydeaths of(over deathstwo million a year) occur in the newborn period,. withAccording overto twoa million[[World worldwideHealth deathsOrganization]] a year. In factestimate, the WHO estimates that one in three newborn infant deaths areresult due tofrom pneumonia.{{an|<ref name=Garenne}} /> Mortality decreases with age until late adulthood;, elderlywith individualsthe are particularlyelderly at risk for CAP and its associated mortality.

More CAP cases of CAP occur during the winter months than duringat other times of the year. CAP occursis more commonlycommon in males than females, and more common in blacksblack people than Caucasians.<ref>{{Cite journal|last1=Ramirez|first1=Julio A|last2=Wiemken|first2=Timothy L|last3=Peyrani|first3=Paula|last4=Arnold|first4=Forest W|last5=Kelley|first5=Robert|last6=Mattingly|first6=William A|last7=Nakamatsu|first7=Raul|last8=Pena|first8=Senen|last9=Guinn|first9=Brian E|date=2017-07-28|title=Adults Hospitalized With Pneumonia in the United States: Incidence, Epidemiology, and Mortality|journal=Clinical Infectious Diseases|language=en|volume=65|issue=11|pages=1806–1812|doi=10.1093/cid/cix647|pmid=29020164|issn=1058-4838|doi-access=free}}</ref> IndividualsPatients with underlying illnesses (such as [[Alzheimer's disease]], [[cystic fibrosis]], [[emphysema]]COPD, [[tobacco smoking]], [[alcoholism]], or [[immunosuppression|immune -system problems]]) arehave atan increased risk forof developing pneumonia.{{an|<ref name=Almirall}} />

The strongest risk factor for CAP is older age (over 65). Other risk factors include smoking (conferring a 1.57X increased risk of CAP)(impaired [[mucociliary clearance]] due to tobacco smoke exposure is thought to be a main driving mechanism), underlying pulmonary disease (1.99X increased risk of CAP), asthma (1.71X), poor oral health (2.78X), poor nutritional status (6.14X), functional impairment (2.13X) and using immunosuppressive drugs (3.10X).<ref name="Vaughn 2024">{{cite journal |last1=Vaughn |first1=Valerie M. |last2=Dickson |first2=Robert P. |last3=Horowitz |first3=Jennifer K. |last4=Flanders |first4=Scott A. |title=Community-Acquired Pneumonia: A Review |journal=JAMA |date=15 October 2024 |volume=332 |issue=15 |pages=1282 |doi=10.1001/jama.2024.14796}}</ref>

== Prevention ==

In addition to treating any underlying illness which can increase a person's risk for CAP, there are several additional ways to prevent CAP. Smoking cessation is important not only for treatment of any underlying lung disease, but also because cigarette smoke interferes with many of the body's natural defenses against CAP.

==See also==

[[Vaccination]] is important in both children and adults. Vaccinations against ''[[Haemophilus influenzae]]'' and ''[[Streptococcus pneumoniae]]'' in the first year of life have greatly reduced their role in CAP in children. A vaccine against ''[[Streptococcus pneumoniae]]'' is also available for adults and is currently recommended for all healthy individuals older than 65 and any adults with [[emphysema]], [[congestive heart failure]], [[diabetes mellitus]], [[cirrhosis]] of the [[liver]], [[alcoholism]], [[cerebrospinal fluid]] leaks, or who do not have a [[asplenia|spleen]]. A repeat vaccination may also be required after five or ten years.{{an|Butler}}

* [[Bacterial pneumonia]]

* [[Viral pneumonia]]

[[Influenza]] vaccines should be given yearly to the same individuals as receive vaccination against ''[[Streptococcus pneumoniae]]''. In addition, health care workers, nursing home residents, and pregnant women should receive the vaccine.{{an|CDC}} When an influenza outbreak is occurring, medications such as [[amantadine]], [[rimantadine]], [[zanamivir]], and [[oseltamivir]] have been shown to prevent cases of influenza.{{an|Hayden}}

* [[Fungal pneumonia]]

* [[Parasitic pneumonia]]

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<ref name=Butler>{{cite journal |vauthors=Butler JC, Breiman RF, Campbell JF, Lipman HB, Broome CV, Facklam RR |title=Pneumococcal polysaccharide vaccine efficacy. An evaluation of current recommendations |journal=JAMA |volume=270 |issue=15 |pages=1826–31 |date=October 1993 |pmid=8411526 |doi=10.1001/jama.270.15.1826}}</ref>

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}}

* {{cite journal |vauthors=Mandell LA, Wunderink RG, Anzueto A |title=Infectious Diseases Society of America/American Thoracic Society consensus guidelines on the management of community-acquired pneumonia in adults |journal=Clinical Infectious Diseases |volume=44 |issue=Suppl 2 |pages=S27–72 |date=March 2007 |pmid=17278083 |doi=10.1086/511159|display-authors=etal|doi-access=free |pmc=7107997 }}

==See alsoExternal links ==

* [https://web.archive.org/web/20140517221823/http://cid.oxfordjournals.org/content/44/Supplement_2/S27.full.pdf+html Infectious Diseases Society of America/American Thoracic Society Consensus Guidelines on the Management of Community-Acquired Pneumonia in Adults PDF]

*[[Pneumonia]]

*[[Nosocomial pneumonia|Hospital-acquired pneumonia]]

{{Respiratory pathology}}

*[[Bacterial pneumonia]]

*[[Viral {{pneumonia]]}}

*[[Fungal pneumonia]]

*[[Parasitic pneumonia]]

*[[Tuberculosis]]

[[Category:Pneumonia]]

{{med-stub}}

[[Category:Pulmonology]]

[[Category:Infectious diseases]]