View source for Classification of pneumonia

{{about|classification of pneumonia|the disease itself|Pneumonia}}
{{Use dmy dates|date=April 2021}}
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| alt             = A black and white X-ray picture showing a triangle white area on the left side. A circle highlights the area.
| caption         = A chest X-ray showing a very prominent wedge-shape [[bacterial pneumonia]] in the right lung
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[[Pneumonia]] can be classified in several ways, most commonly by where it was acquired (hospital versus community), but may also by the area of lung affected or by the causative organism.<ref name="pmid16013205">{{cite journal |vauthors=Dunn L |title=Pneumonia: classification, diagnosis and nursing management |journal=Nurs Stand |volume=19 |issue=42 |pages=50–4 |year=2005 |pmid=16013205 |doi=10.7748/ns2005.06.19.42.50.c3901}}</ref> There is also a combined clinical classification, which combines factors such as age, risk factors for certain microorganisms, the presence of underlying lung disease or systemic disease and whether the person has recently been hospitalized.
==By location acquired==
===Community-acquired===
{{Main|Community-acquired pneumonia}}
[[Community-acquired pneumonia]] (CAP) is infectious pneumonia in a person who has not recently been hospitalized. CAP is the most common type of pneumonia. The most common causes of CAP vary depending on a person's age, but they include ''[[Streptococcus pneumoniae]]'', viruses, the atypical bacteria, and ''[[Haemophilus influenzae]]''. Overall, ''Streptococcus pneumoniae'' is the most common cause of community-acquired pneumonia worldwide. [[Gram-negative bacteria]] cause CAP in certain at-risk populations. CAP is the fourth most common cause of death in the United Kingdom and the sixth in the United States. The term "walking pneumonia" has been used to describe a type of community-acquired pneumonia of less severity (because the sufferer can continue to "walk" rather than requiring hospitalization).<ref>{{cite web |url=http://www.uptodate.com/online/content/topic.do?topicKey=pedi_id/18313&selectedTitle=1~1&source=search_result |title=UpToDate Inc. }}</ref> Walking pneumonia is usually caused by the atypical bacterium, ''[[Mycoplasma pneumoniae]]''.<ref>{{cite journal |vauthors=Krause DC, Balish MF |title=Cellular engineering in a minimal microbe: structure and assembly of the terminal organelle of Mycoplasma pneumoniae |journal=Mol. Microbiol. |volume=51 |issue=4 |pages=917–24 |date=February 2004 |pmid=14763969 |doi= 10.1046/j.1365-2958.2003.03899.x|doi-access=free }}</ref>
===Hospital-acquired===
{{Main|Hospital-acquired pneumonia}}
Hospital-acquired pneumonia, also called [[Nosocomial infection|nosocomial]] pneumonia, is pneumonia acquired during or after hospitalization for another illness or procedure with onset at least 72 hrs after admission. The causes, microbiology, treatment and prognosis are different from those of community-acquired pneumonia. Up to 5% of patients admitted to a hospital for other causes subsequently develop pneumonia. Hospitalized patients may have many risk factors for pneumonia, including [[mechanical ventilation]], prolonged [[malnutrition]], underlying [[heart]] and [[lung]] diseases, decreased amounts of stomach acid, and immune disturbances. Additionally, the microorganisms a person is exposed to in a hospital are often different from those at home. Hospital-acquired microorganisms may include resistant bacteria such as [[Methicillin-resistant Staphylococcus aureus|MRSA]], ''[[Pseudomonas]]'', ''[[Enterobacter]]'', and ''[[Serratia]]''. Because individuals with hospital-acquired pneumonia usually have underlying illnesses and are exposed to more dangerous bacteria, it tends to be more deadly than community-acquired pneumonia. [[Ventilator-associated pneumonia]] (VAP) is a subset of hospital-acquired pneumonia. VAP is pneumonia which occurs after at least 48 hours of [[intubation]] and [[mechanical ventilation]].
==By cause==
Pneumonia has historically been characterized as either typical or [[atypical pneumonia|atypical]] depending on the presenting symptoms and thus the presumed underlying organism.<ref name=EBMED05>{{cite journal|last=Ebby|first=Orin|title=Community-Acquired Pneumonia: From Common Pathogens To Emerging Resistance|journal=Emergency Medicine Practice|date=Dec 2005|volume=7|issue=12|url=https://www.ebmedicine.net/topics.php?paction=showTopic&topic_id=118}}</ref> Attempting to make this distinction based on symptoms, however, has not been found to be accurate, and [[The American Thoracic Society]] does not recommend its use.<ref name=EBMED05/>
===Bronchiolitis obliterans organizing pneumonia===
:[[Bronchiolitis obliterans organizing pneumonia]] (BOOP) is caused by inflammation of the small airways of the lungs. It is also known as cryptogenic organizing pneumonitis (COP).
;Eosinophilic pneumonia
:[[Eosinophilic pneumonia]] is invasion of the lung by [[eosinophil]]s, a particular kind of [[white blood cell]]. Eosinophilic pneumonia often occurs in response to infection with a [[parasite]] or after exposure to certain types of environmental factors.
===Chemical pneumonia===
:[[Chemical pneumonia]] (usually called [[chemical pneumonitis]]) is caused by chemical [[toxicant]]s such as [[pesticide]]s, which may enter the body by [[inhalation]] or by skin contact. When the toxic substance is an oil, the pneumonia may be called ''lipoid pneumonia''.
===Aspiration pneumonia===
:[[Aspiration pneumonia]] (or aspiration pneumonitis) is caused by [[Pulmonary aspiration|aspirating]] foreign objects which are usually oral or gastric contents, either while eating, or after reflux or vomiting which results in [[bronchopneumonia]]. The resulting lung inflammation is not an infection but can contribute to one, since the material aspirated may contain [[Anaerobic organism|anaerobic]] bacteria or other unusual causes of pneumonia. Aspiration is a leading cause of death among hospital and [[nursing home]] patients, since they often cannot adequately protect their airways and may have otherwise impaired defenses.
===Dust pneumonia===
:[[Dust pneumonia]] describes disorders caused by excessive exposure to [[dust storms]], particularly during the [[Dust Bowl]] in the United States. With dust pneumonia, dust settles all the way into the alveoli of the lungs, stopping the cilia from moving and preventing the lungs from ever clearing themselves.
===Necrotizing pneumonia===
{{Main|Necrotizing pneumonia}}
:'''Necrotizing pneumonia''' (NP), also known as '''cavitary pneumonia''' or '''cavitatory necrosis''', is a rare but severe complication of [[lung]] [[Parenchyma#Lungs|parenchymal]] [[infection]].<ref name="Sawicki Lu Valim Cleveland pp. 1285–1291">{{cite journal|last1=Sawicki|first1=G. S.|last2=Lu|first2=F. L.|last3=Valim|first3=C.|last4=Cleveland|first4=R. H.|last5=Colin|first5=A. A.|date=2008-03-05|title=Necrotising pneumonia is an increasingly detected complication of pneumonia in children|journal=European Respiratory Journal|volume=31|issue=6|pages=1285–1291|doi=10.1183/09031936.00099807|pmid=18216055|issn=0903-1936|doi-access=free}}</ref><ref name="TsaiKu2012">{{cite journal|last1=Tsai|first1=Yueh-Feng|last2=Ku|first2=Yee-Huang|year=2012|title=Necrotizing pneumonia|journal=Current Opinion in Pulmonary Medicine|volume=18|issue=3|pages=246–252|doi=10.1097/MCP.0b013e3283521022|pmid=22388585|issn=1070-5287}}</ref><ref name="Masters Isles Grimwood p.">{{cite journal|last1=Masters|first1=I. Brent|last2=Isles|first2=Alan F.|last3=Grimwood|first3=Keith|date=July 25, 2017|title=Necrotizing pneumonia: an emerging problem in children?|journal=Pneumonia|volume=9|issue=1|page=11|doi=10.1186/s41479-017-0035-0|pmid=28770121|pmc=5525269|issn=2200-6133|doi-access=free}}</ref> In necrotizing pneumonia, there is a substantial [[liquefactive necrosis|liquefaction]] following death of the lung tissue, which may lead to [[gangrene]] formation in the lung.<ref name="Scotta Marostica Stein 2019 pp. 427–438.e4">{{cite book|last1=Scotta|first1=Marcelo C.|title=Kendig's Disorders of the Respiratory Tract in Children|last2=Marostica|first2=Paulo J.C.|last3=Stein|first3=Renato T.|year=2019|publisher=Elsevier|isbn=978-0-323-44887-1|pages=435.e4|chapter=Pneumonia in Children|doi=10.1016/b978-0-323-44887-1.00025-0|s2cid=81700501}}</ref><ref name="Widysanto Liem Puspita Pradhana p.">{{cite journal | last1=Widysanto | first1=Allen | last2=Liem | first2=Maranatha | last3=Puspita | first3=Karina Dian | last4=Pradhana | first4=Cindy Meidy Leony | title=Management of necrotizing pneumonia with bronchopleural fistula caused by multidrug‐resistant Acinetobacter baumannii | journal=Respirology Case Reports | year=2020 | volume=8 | issue=8 | pages=e00662 | pmid=32999723 | doi=10.1002/rcr2.662 | pmc=7507560 | doi-access=free }}</ref> In most cases patients with NP have [[fever]], [[cough]] and [[bad breath]], and those with more indolent infections have weight loss.<ref name="Reimel Krishnadasen Cuschieri Klein 2000 p.">{{cite journal | last1=Reimel | first1=Beth Ann | last2=Krishnadasen | first2=Baiya | last3=Cuschieri | first3=Joseph | last4=Klein | first4=Matthew B | last5=Gross | first5=Joel | last6=Karmy-Jones | first6=Riyad | title=Surgical management of acute necrotizing lung infections | journal=Canadian Respiratory Journal | volume=13 | issue=7 | date=January 1, 2000 | pages=369–373 | pmid=17036090 | doi=10.1155/2006/760390 | pmc=2683290 | doi-access=free }}</ref> Often patients clinically present with acute respiratory failure.<ref name="Reimel Krishnadasen Cuschieri Klein 2000 p."/> The most common pathogens responsible for NP are ''[[Streptococcus pneumoniae]]'', ''[[Staphylococcus aureus]]'', ''[[Klebsiella pneumoniae]]''.<ref name="Krutikov Rahman Tiberi 2019 pp. 225–232">{{cite journal | last1=Krutikov | first1=Maria | last2=Rahman | first2=Ananna | last3=Tiberi | first3=Simon | title=Necrotizing pneumonia (aetiology, clinical features and management) | journal=Current Opinion in Pulmonary Medicine | volume=25 | issue=3 | year=2019 | issn=1070-5287 | doi=10.1097/mcp.0000000000000571 | pages=225–232| pmid=30844921 | s2cid=73507080 }}</ref>
===Opportunistic pneumonia===
:People with [[Immunocompromised|weakened immune defense]], such as [[AIDS|HIV/AIDS]] patients, are highly susceptible to [[opportunistic infections]] affecting the lungs.<ref name="Current Problems in Diagnostic Radiology 1993 pp. 5–35">{{cite journal | title=Opportunistic pneumonia | journal=Current Problems in Diagnostic Radiology | volume=22 | issue=1 | date=January 1, 1993 | issn=0363-0188 | doi=10.1016/0363-0188(93)90005-E | pages=5–35 | url=https://www.sciencedirect.com/science/article/abs/pii/036301889390005E | access-date=February 23, 2021| last1=Conces | first1=Dewey J. | pmid=8428506 }}</ref> Most common pathogens are ''[[Pneumocystis jiroveci]]'', ''[[Mycobacterium avium-intracellulare]]'' complex, ''[[Streptococcus pneumoniae]]'', ''[[Haemophilus]]'' species. Less frequent pathogens are ''[[Cryptococcus neoformans]]'', ''[[Histoplasma capsulatum]]'', ''[[Coccidioides immitis]]'', [[cytomegalovirus]] (CMV), and ''[[Toxoplasma gondii]]''.<ref name="Huang Crothers p.">{{cite journal | last1=Huang | first1=Laurence | last2=Crothers | first2=Kristina A. | title=HIV-associated Opportunistic Pneumonias | journal=Respirology | year=2009 | volume=14 | issue=4 | pages=474–485 | pmid=19645867 | doi=10.1111/j.1440-1843.2009.01534.x | pmc=2835537 | doi-access=free }}</ref>
:Chemotherapy-induced immunodeficiency may lead to severe lung infections.<ref name="Vento Cainelli Temesgen 2008 pp. 982–992" /> Pathogens commonly associated with lung infectioins are bacteria (like ''[[Pseudomonas aeruginosa]]'', ''[[Stenotrophomonas maltophilia]]'', and ''[[Nocardia]]'' species), viruses (eg, [[respiratory syncytial virus]], [[parainfluenza virus]], [[influenza virus A]] and [[influenza B]], and cytomegalovirus), and fungi (e.g. ''[[Aspergillus]]'', ''[[Fusarium]]'', and [[Mucorales]] species, and ''Pneumocystis jirovecii'').<ref name="Vento Cainelli Temesgen 2008 pp. 982–992">{{cite journal | last1=Vento | first1=Sandro | last2=Cainelli | first2=Francesca | last3=Temesgen | first3=Zelalem | title=Lung infections after cancer chemotherapy | journal=The Lancet Oncology | volume=9 | issue=10 | date=October 1, 2008 | issn=1470-2045 | pmid=19071255 | doi=10.1016/S1470-2045(08)70255-9 | pages=982–992 | url=https://www.thelancet.com/journals/lanonc/article/PIIS1470-2045(08)70255-9/abstract | access-date=February 23, 2021}}</ref>
===Double pneumonia (bilateral pneumonia)===
:This is a historical term for [[acute lung injury]] (ALI) or [[acute respiratory distress syndrome]] (ARDS).<ref>{{cite journal |vauthors=Girard TD, Bernard GR |title=Mechanical ventilation in ARDS: a state-of-the-art review |journal=Chest |volume=131 |issue=3 |pages=921–9 |date=March 2007 |pmid=17356115 |doi=10.1378/chest.06-1515 }}</ref> However, the term was and, especially by lay people, still is used to denote pneumonia affecting both lungs. Accordingly, the term 'double pneumonia' is more likely to be used to describe bilateral pneumonia than it is ALI or ARDS.
===Severe acute respiratory syndrome===
:[[Severe acute respiratory syndrome]] (SARS) is a highly contagious and deadly type of pneumonia which first occurred in November 2002 after initial outbreaks in China caused by [[SARS-CoV]], which had almost disappeared by the month of May 2004 (it was later called SARS-CoV-1 to distinguish it from other similar viruses). The second outbreak, [[SARS-CoV-2]], started in December 2019 from Wuhan, China and was declared pandemic by the WHO on 11 March 2020. SARS is caused by the [[SARS coronavirus]], a previously unknown [[pathogen]].
==By area of lung affected==
Initial descriptions of pneumonia focused on the [[anatomic]] or [[pathology|pathologic]] appearance of the lung, either by direct inspection at [[autopsy]] or by its appearance under a [[microscope]].
* A [[Lobar pneumonia|''lobar'' pneumonia]] is an infection that only involves a single lobe, or section, of a [[lung]]. Lobar pneumonia is often due to ''[[Streptococcus pneumoniae]]'' (though ''[[Klebsiella pneumoniae]]'' is also possible.)<ref name="pmid1792415">{{cite journal |vauthors=Feldman C, Kallenbach JM, Levy H, Thorburn JR, Hurwitz MD, Koornhof HJ |title=Comparison of bacteraemic community-acquired lobar pneumonia due to Streptococcus pneumoniae and Klebsiella pneumoniae in an intensive care unit |journal=Respiration |volume=58 |issue=5–6 |pages=265–70 |year=1991 |pmid=1792415 |doi=10.1159/000195943}}</ref>
* ''Multilobar'' pneumonia involves more than one lobe, and it often causes a more severe illness.
* [[Bronchial pneumonia]] affects the lungs in patches around the tubes (bronchi or bronchioles).
* [[Usual interstitial pneumonia|''Interstitial'' pneumonia]] involves the areas in between the alveoli, and it may be called "interstitial pneumonitis." It is more likely to be caused by viruses or by atypical bacteria.
The discovery of x-rays made it possible to determine the anatomic type of pneumonia without direct examination of the lungs at autopsy and led to the development of a [[radiology|radiological]] classification. Early investigators distinguished between typical lobar pneumonia and atypical (e.g. ''Chlamydophila'') or viral pneumonia using the location, distribution, and appearance of the opacities they saw on chest x-rays. Certain x-ray findings can be used to help predict the course of illness, although it is not possible to clearly determine the microbiologic cause of a pneumonia with x-rays alone.
With the advent of modern microbiology, classification based upon the causative microorganism became possible. Determining which microorganism is causing an individual's pneumonia is an important step in deciding treatment type and length. Sputum cultures, blood cultures, tests on respiratory secretions, and specific blood tests are used to determine the microbiologic classification. Because such laboratory testing typically takes several days, microbiologic classification is usually not possible at the time of initial diagnosis.
<gallery>
File:Normal AP.JPG|Normal AP CXR
File:Normal lateral chest x-ray.jpg|Normal lateral CXR
File:LLL_pneumonia_with_effusionM.jpg|AP CXR showing left lower lobe pneumonia associated with a small left sided pleural effusion
File:RLL_pneumoniaM.jpg|AP CXR showing right lower lobe pneumonia
File:Pneumnia1.jpg|AP CXR showing pneumonia of the lingula of the left lung
File:PneumoniaRUL.jpg|Right upper lobe pneumonia as marked by the circle.
File:PneumoLLL.PNG|Left upper lobe pneumonia with a small pleural effusion.
File:RLLpneumonia.PNG|Right lower lobe pneumonia as seen on a lateral CXR
</gallery>
==Clinical==
Traditionally, clinicians have classified pneumonia by clinical characteristics, dividing them into "acute" (less than three weeks duration) and "chronic" pneumonias. This is useful because chronic pneumonias tend to be either non-infectious, or mycobacterial, fungal, or mixed bacterial infections caused by airway obstruction. Acute pneumonias are further divided into the classic bacterial bronchopneumonias (such as ''[[Streptococcus pneumoniae]]''), the atypical pneumonias (such as the interstitial pneumonitis of ''[[Mycoplasma pneumoniae]]'' or ''[[Chlamydia pneumoniae]]''), and the aspiration pneumonia syndromes.{{citation needed|date=April 2021}}
Chronic pneumonias, on the other hand, mainly include those of ''[[Nocardia]]'', ''[[Actinomyces]]'' and ''[[Blastomyces dermatitidis]]'', as well as the granulomatous pneumonias (''[[Mycobacterium tuberculosis]]'' and [[atypical mycobacteria]], ''[[Histoplasma capsulatum]]'' and ''[[Coccidioides immitis]]'').<ref name=Kumar13-7>Table 13-7 in: {{cite book |author1=Mitchell, Richard Sheppard |author2=Kumar, Vinay |author3=Abbas, Abul K. |author4=Fausto, Nelson |title=Robbins Basic Pathology|publisher=Saunders |location=Philadelphia |year= 2007 |isbn=978-1-4160-2973-1 |edition=8th}}</ref>
The combined clinical classification, now the most commonly used classification scheme, attempts to identify a person's risk factors when he or she first comes to medical attention. The advantage of this classification scheme over previous systems is that it can help guide the selection of appropriate initial treatments even before the microbiologic cause of the pneumonia is known. There are two broad categories of pneumonia in this scheme: community-acquired pneumonia and hospital-acquired pneumonia. A recently{{when|date=April 2021}} introduced type of [[healthcare-associated pneumonia]] (in patients living outside the hospital who have recently been in close contact with the health care system) lies between these two categories.{{citation needed|date=April 2021}}
==References==
{{reflist}}
== External links ==
{{Medical resources
|  DiseasesDB      = 10166
|  ICD10           = {{ICD10|J|12||j|09}}, {{ICD10|J|13||j|09}}, {{ICD10|J|14||j|09}}, {{ICD10|J|15||j|09}}, {{ICD10|J|16||j|09}}, {{ICD10|J|17||j|09}}, {{ICD10|J|18||j|09}}, {{ICD10|P|23||p|20}}
|  ICD9            = {{ICD9|480}}-{{ICD9|486}}, {{ICD9|770.0}}
|  ICDO            =
|  OMIM            =
|  MedlinePlus     = 000145
|  eMedicineSubj   = search
|  eMedicineTopic  = pneumonia
|  MeshID          = D011014
}}
{{Pneumonia}}
[[Category:Pneumonia]]
[[Category:Medical classification]]