Editing Pneumonia (section)

==Cause==
[[File:Streptococcus pneumoniae.jpg|thumb|alt=Three lone round objects in a black background|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.<ref name=Lancet11/> A causative agent may not be isolated in about half of cases despite careful testing.<ref name=EBMED05/> 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.<ref name="EPIC2015">{{cite journal | vauthors = Jain S, Self WH, Wunderink RG, Fakhran S, Balk R, Bramley AM, Reed C, Grijalva CG, Anderson EJ, Courtney DM, Chappell JD, Qi C, Hart EM, Carroll F, Trabue C, Donnelly HK, Williams DJ, Zhu Y, Arnold SR, Ampofo K, Waterer GW, Levine M, Lindstrom S, Winchell JM, Katz JM, Erdman D, Schneider E, Hicks LA, McCullers JA, Pavia AT, Edwards KM, Finelli L | title = Community-Acquired Pneumonia Requiring Hospitalization among U.S. Adults | journal = The New England Journal of Medicine | volume = 373 | issue = 5 | pages = 415–27 | date = July 2015 | pmid = 26172429 | pmc = 4728150 | doi = 10.1056/NEJMoa1500245 }}</ref> Most patients (62%) had no detectable pathogens in their sample, and unexpectedly, respiratory viruses were detected more frequently than bacteria.<ref name="EPIC2015"/> 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%)."<ref name="EPIC2015"/>

The term ''pneumonia'' is sometimes more broadly applied to any condition resulting in [[inflammation]] of the lungs (caused for example by [[autoimmune disease]]s, chemical burns or drug reactions); however, this inflammation is more accurately referred to as [[pneumonitis]].<ref name="isbn0-7234-3200-7"/><ref name=Bowden2010/>

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]].<ref name=Clinic2011/><ref>{{cite book|editor-last=Marrie|editor-first=Thomas J. |title=Community-acquired pneumonia|date=2002|publisher=Kluwer Academic Publishers|location=New York|isbn=978-0-306-46834-6|page=20|url=https://books.google.com/books?id=Yc0RBwAAQBAJ&pg=PA20}}</ref><ref name=CDC2020SCD/> Additional risks in children include not being [[breastfeeding|breastfed]], exposure to cigarette smoke and other air pollution, malnutrition, and poverty.<ref>{{cite journal | vauthors = Nguyen TK, Tran TH, Roberts CL, Fox GJ, Graham SM, Marais BJ | title = Risk factors for child pneumonia – focus on the Western Pacific Region | journal = Paediatric Respiratory Reviews | volume = 21 | pages = 95–101 | date = January 2017 | pmid = 27515732 | doi = 10.1016/j.prrv.2016.07.002 }}</ref> The use of acid-suppressing medications – such as [[proton-pump inhibitors]] or [[H2 blockers]] – is associated with an increased risk of pneumonia.<ref>{{cite journal | vauthors = Eom CS, Jeon CY, Lim JW, Cho EG, Park SM, Lee KS | title = Use of acid-suppressive drugs and risk of pneumonia: a systematic review and meta-analysis | journal = CMAJ | volume = 183 | issue = 3 | pages = 310–19 | date = February 2011 | pmid = 21173070 | pmc = 3042441 | doi = 10.1503/cmaj.092129 }}</ref> Approximately 10% of people who require [[mechanical ventilation]] develop [[ventilator-associated pneumonia]],<ref name="Ar2016">{{cite journal | vauthors = Arthur LE, Kizor RS, Selim AG, van Driel ML, Seoane L | title = Antibiotics for ventilator-associated pneumonia | journal = The Cochrane Database of Systematic Reviews | volume = 2016 | pages = CD004267 | date = October 2016 | issue = 10 | pmid = 27763732 | pmc = 6461148 | doi = 10.1002/14651858.CD004267.pub4 }}</ref> and people with a [[gastric feeding tube]] have an increased risk of developing [[aspiration pneumonia]].<ref>{{cite journal | vauthors = Alkhawaja S, Martin C, Butler RJ, Gwadry-Sridhar F | title = Post-pyloric versus gastric tube feeding for preventing pneumonia and improving nutritional outcomes in critically ill adults | journal = The Cochrane Database of Systematic Reviews | issue = 8 | pages = CD008875 | date = August 2015 | volume = 2018 | pmid = 26241698 | pmc = 6516803 | doi = 10.1002/14651858.CD008875.pub2 }}</ref> Moreover, the misplacement of a feeding tube can lead to aspiration pneumonia. 28% of tube malposition results in pneumonia.<ref>{{cite web |date=5 March 2013 |title=Interprofessional Task force Uses a collaborative approach for internal feeding tube management |url=https://issuu.com/umms/docs/nv-winter_2013 |access-date=16 January 2023 |website=News and Views |page=10 |language=en}}</ref><ref>{{cite journal |date=17 November 2016 |title=ASPEN Safe Practices for Enteral Nutrition Therapy |url=https://eclass.hua.gr/modules/document/file.php/DIET159/JPEN%20J%20Parenter%20Enteral%20Nutr-2016-Boullata-0148607116673053.pdf |journal=Journal of Parenteral and Enteral Nutrition |volume=XX |issue=X |access-date=16 January 2023 |archive-date=16 January 2023 |archive-url=https://web.archive.org/web/20230116100215/https://eclass.hua.gr/modules/document/file.php/DIET159/JPEN%20J%20Parenter%20Enteral%20Nutr-2016-Boullata-0148607116673053.pdf }}</ref> As with [[Avanos Medical]]'s feeding tube placement system, the CORTRAK* 2 EAS, which was recalled in May 2022 by the [[Food and Drug Administration|FDA]] due to adverse events reported, including pneumonia, caused a total of 60 injuries and 23 patient deaths, as communicated by the FDA.<ref>{{cite journal |date=21 March 2022 |title=Urgent: Field Correction Cortrak* 2 Enteral Access System (EAS) |url=https://static.foxnews.com/foxnews.com/content/uploads/2022/04/Avanos_CORTRAK2_Field_Correction_Letter.pdf |journal=Avanos |pages=1–2}}</ref><ref>{{cite web |last=Park |first=Andrea |date=16 May 2022 |title=Avanos Medical faces Class I recall for feeding tube system linked to 23 deaths since 2015 |url=https://www.fiercebiotech.com/medtech/avanos-medical-faces-class-i-recall-feeding-tube-system-linked-23-deaths-2015 |access-date=16 January 2023 |website=Fierce Biotech |language=en}}</ref><ref>{{cite journal |last=Health |first=Center for Devices and Radiological |date=16 May 2022 |title=Avanos Medical Recalls Cortrak*2 Enteral Access System for Risk of Misplaced Enteral Tubes Could Cause Patient Harm |url=https://www.fda.gov/medical-devices/medical-device-recalls/avanos-medical-recalls-cortrak2-enteral-access-system-risk-misplaced-enteral-tubes-could-cause |journal=FDA |language=en}}</ref> For people with certain variants of the [[FER (gene)|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.<ref name="Elena 2015"/>

===Bacteria===
{{Main|Bacterial pneumonia}}
[[File:MRSAPneumoCT.png|thumb|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.<ref name=Rad07/><ref name=EOP10>{{cite journal | vauthors = Anevlavis S, Bouros D | title = Community acquired bacterial pneumonia | journal = Expert Opinion on Pharmacotherapy | volume = 11 | issue = 3 | pages = 361–74 | date = February 2010 | pmid = 20085502 | doi = 10.1517/14656560903508770 | s2cid = 24376187 }}</ref> Other commonly isolated bacteria include ''[[Haemophilus influenzae]]'' in 20%, ''[[Chlamydophila pneumoniae]]'' in 13%, and ''Mycoplasma pneumoniae'' in 3% of cases;<ref name=Rad07/> ''[[Staphylococcus aureus]]''; ''[[Moraxella catarrhalis]]''; and ''[[Legionella pneumophila]]''.<ref name=EBMED05/> A number of [[drug resistance|drug-resistant]] versions of the above infections are becoming more common, including drug-resistant ''Streptococcus pneumoniae'' (DRSP) and [[methicillin-resistant Staphylococcus aureus|methicillin-resistant ''Staphylococcus aureus'']] (MRSA).<ref name=Clinic2011/>

The spreading of organisms is facilitated by certain risk factors.<ref name=EBMED05/> Alcoholism is associated with ''Streptococcus pneumoniae'', [[anaerobic organism]]s, 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''.<ref name=EBMED05/> ''Streptococcus pneumoniae'' is more common in the winter,<ref name=EBMED05/> and it should be suspected in persons aspirating a large number of anaerobic organisms.<ref name=Clinic2011/>

===Viruses===
{{Main|Viral pneumonia}}
[[File:SARS xray.jpg|thumb|A chest x-ray of a patient with severe viral pneumonia due to [[Severe acute respiratory syndrome|SARS]]]]
In adults, viruses account for about one third of pneumonia cases,<ref name=Lancet11/> and in children for about 15% of them.<ref name=M31/> Commonly implicated agents include [[rhinovirus]]es, [[coronavirus]]es, [[influenza virus]], [[respiratory syncytial virus]] (RSV), [[adenovirus]], and [[parainfluenza]].<ref name=Lancet11/><ref name=Viral09/> [[Herpes simplex virus]] rarely causes pneumonia, except in groups such as newborns, persons with cancer, transplant recipients, and people with significant burns.<ref name=Text2010>{{cite book|vauthors=Behera D|title=Textbook of pulmonary medicine|year=2010|publisher=Jaypee Brothers Medical Pub.|location=New Delhi|isbn=978-81-8448-749-7|pages=391–94|url=https://books.google.com/books?id=0TbJjd9eTp0C&pg=PA391|edition=2nd}}{{Dead link|date=September 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> After [[organ transplantation]] or in otherwise [[immunocompromised]] persons, there are high rates of [[cytomegalovirus]] pneumonia.<ref name=M31/><ref name=Text2010/> 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.<ref name=Clinic2011/><ref name=M31/> 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.<ref name=M31/> Outbreaks of other viruses also occur occasionally, including [[hantaviruses]] and coronaviruses.<ref name=M31/> [[Severe acute respiratory syndrome coronavirus 2]] (SARS-CoV-2) can also result in pneumonia.<ref>{{cite journal | vauthors = Lai CC, Shih TP, Ko WC, Tang HJ, Hsueh PR | title = Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and coronavirus disease-2019 (COVID-19): The epidemic and the challenges | journal = International Journal of Antimicrobial Agents | volume = 55 | issue = 3 | page = 105924 | date = March 2020 | pmid = 32081636 | pmc = 7127800 | doi = 10.1016/j.ijantimicag.2020.105924 | doi-access = free }}</ref>

===Fungi===
{{Main|Fungal pneumonia}}

Fungal pneumonia is uncommon, but occurs more commonly in individuals with weakened immune systems due to AIDS, [[immunosuppressive drug]]s, or other medical problems.<ref name=EBMED05/><ref name=Fungus2009>{{cite book|last1=Maskell|first1=Nick | last2 = Millar | first2 = Ann |title=Oxford Desk Reference: Respiratory Medicine |year=2009|publisher=Oxford University Press|location=Oxford | isbn = 978-0-19-923912-2 |page=196|url=https://books.google.com/books?id=MfEUkzQQ1BEC&pg=PA196}}</ref> It is most often caused by ''[[Histoplasmosis|Histoplasma capsulatum]]'', ''[[Blastomyces]]'', ''[[Cryptococcus neoformans]]'', ''[[Pneumocystis jiroveci]]'' ([[pneumocystis pneumonia]], or PCP), and ''[[Coccidioides immitis]]''. Histoplasmosis is most common in the [[Mississippi embayment|Mississippi River basin]], and [[coccidioidomycosis]] is most common in the Southwestern United States.<ref name=EBMED05/> 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.<ref name=Fungus2009/> For people infected with [[HIV/AIDS]], PCP is a common [[opportunistic infection]].<ref name=Ewa2015>{{cite journal | vauthors = Ewald H, Raatz H, Boscacci R, Furrer H, Bucher HC, Briel M | title = Adjunctive corticosteroids for Pneumocystis jiroveci pneumonia in patients with HIV infection | journal = The Cochrane Database of Systematic Reviews | issue = 4 | pages = CD006150 | date = April 2015 | volume = 2015 | pmid = 25835432 | pmc = 6472444 | doi = 10.1002/14651858.CD006150.pub2 }}</ref>

===Parasites===
{{Main|Parasitic pneumonia}}
A variety of [[parasite]]s can affect the lungs, including ''[[Toxoplasma gondii]]'', ''[[Strongyloides stercoralis]]'', ''[[Ascaris lumbricoides]]'', and ''[[Plasmodium malariae]]''.<ref name=M37>Murray and Nadel (2010). Chapter 37.</ref> These organisms typically enter the body through direct contact with the skin, ingestion, or via an insect vector.<ref name=M37/> Except for ''[[Paragonimus westermani]]'', most parasites do not specifically affect the lungs but involve the lungs secondarily to other sites.<ref name=M37/> Some parasites, in particular those belonging to the ''Ascaris'' and ''Strongyloides'' genera, stimulate a strong [[eosinophilic]] reaction, which may result in [[eosinophilic pneumonia]].<ref name=M37/> In other infections, such as malaria, lung involvement is due primarily to [[cytokine]]-induced [[systemic inflammation]].<ref name=M37/> In the [[developed world]], these infections are most common in people returning from travel or in immigrants.<ref name=M37/> Around the world, parasitic pneumonia is most common in the immunodeficient.<ref>{{cite journal | vauthors = Vijayan VK | title = Parasitic lung infections | journal = Current Opinion in Pulmonary Medicine | volume = 15 | issue = 3 | pages = 274–82 | date = May 2009 | pmid = 19276810 | doi = 10.1097/MCP.0b013e328326f3f8 | s2cid = 2631717 }}</ref>

===Noninfectious===
{{Main|Idiopathic interstitial pneumonia}}

Idiopathic interstitial pneumonia or noninfectious pneumonia<ref>{{cite book|editor-last=Root|editor-first=Richard K.|title=Clinical infectious diseases: a practical approach|year=1999|publisher=Oxford Univ. Press|location=New York [u.a.]|isbn=978-0-19-508103-9|page=833|url=https://books.google.com/books?id=zvCOpighJggC&pg=PA833}}</ref> is a class of [[diffuse lung disease]]s. 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]].<ref>{{cite book| veditors = Costabel U |title=Diffuse parenchymal lung disease: 47 tables|year=2007|publisher=Karger|location=Basel|isbn=978-3-8055-8153-0|page=4|edition=[Online-Ausg.]}}</ref> [[Lipoid pneumonia]] is another rare cause due to [[lipids]] entering the lung.<ref name=Had2010/> These lipids can either be inhaled or spread to the lungs from elsewhere in the body.<ref name="Had2010">{{cite journal |vauthors=Hadda V, Khilnani GC |date=December 2010 |title=Lipoid pneumonia: an overview |url=https://www.worldcat.org/title/262559133 |journal=Expert Review of Respiratory Medicine |volume=4 |issue=6 |pages=799–807 |doi=10.1586/ers.10.74 |oclc=262559133 |pmid=21128754 |s2cid=44309610}}</ref>