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{{CMG}}; '''Associate Editor(s)-In-Chief:''' [[Priyamvada Singh|Priyamvada Singh, M.D.]] [mailto:psingh@perfuse.org]
__NOTOC__
{{Pneumonia}}
{{Pneumonia}}
{{CMG}}; {{AE}} {{HQ}}, [[Priyamvada Singh|Priyamvada Singh, M.D.]] [mailto:psingh13579@gmail.com]; {{AL}}; {{Ochuko}}
==Overview==
==Overview==
[[Pneumonia]] can be caused by viral, bacterial, and fungal organisms. The etiology depends upon various factors like age, immune status, geographical area, and comorbid conditions.
Pneumonia can result from a variety of causes, including infection with [[bacteria]], [[viruses]], [[fungi]], [[parasites]], and chemical or physical injury to the lungs. The etiology will depend upon various factors such as age, immune status, geographical area, and comorbidities.


==Causes==
==Causes==
* Newborn [[infant]]s, [[children]], and [[adult]]s are at risk for different spectrums of disease causing microorganisms.
===Life Threatening Causes===
* In addition, adults with [[chronic (medicine)|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.
Life-threatening causes include conditions which may result in death or permanent disability within 24 hours if left untreated.
 
*[[Anthrax]]
 
===Common Causes===
*[[Cryptococcus neoformans]]
*[[Flu]]
*[[Histoplasmosis]]
*[[Hospital-acquired pneumonia]]
*[[Mycoplasma pneumonia]]
*[[Pneumocystis jiroveci]]
*[[Respiratory syncytial virus]]
*[[Rhinovirus]]
*[[Streptococcus pneumoniae]]
 
===Causes by Pathogen===
 
:'''''[[Bacterial pneumonia|Click here for bacterial pneumonia]]'''''<br>
:'''''[[Viral pneumonia|Click here for viral pneumonia]]'''''<br>
:'''''[[Fungal pneumonia|Click here for fungal pneumonia]]'''''<br>
 
===Infants===
===Infants===
====Source of infection====
====Source of Infection====
* Aerosol
* [[Aerosol]]
* [[Aspiration of amniotic fluid]]
* [[Aspiration pneumonia|Aspiration]] of amniotic fluid
* Blood-borne infection across the [[placenta]]
* Blood-borne [[infection]] across the [[placenta]]
=====Newborn=====
=====Newborn=====
* Most common cause is [[Streptococcus agalactiae]] (Group B Streptococcus)
* Most common cause is [[Streptococcus agalactiae]] ([[Group B streptococcal infection|Group B Streptococcus]])
* GBS causes at least 50% of cases of CAP in the first week of life.{{ref|Webber}}
* [[GBS]] causes at least 50% of cases of CAP in the first week of life.<ref name="pmid2107797">{{cite journal| author=Webber S, Wilkinson AR, Lindsell D, Hope PL, Dobson SR, Isaacs D| title=Neonatal pneumonia. | journal=Arch Dis Child | year= 1990 | volume= 65 | issue= 2 | pages= 207-11 | pmid=2107797 | doi= | pmc=PMC1792235 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=2107797  }} </ref>
* Other bacterial causes in the newborn period include ''[[Listeria monocytogenes]]'' and [[tuberculosis]]
* Other [[Bacteria|bacterial]] causes in the newborn period include ''[[Listeria monocytogenes]]'' and [[tuberculosis]]
* Viral causes like [[herpes simplex virus]] (most common) [[adenovirus]], [[mumps]], and [[enterovirus]]
* [[Virus|Viral]] causes like [[herpes simplex virus]] (most common) [[adenovirus]], [[mumps]], and [[enterovirus]]


===Children===
===Children===
* For the most part, children older than one month are at risk for the same microorganisms as adults.
* For the most part, children older than one month are at risk for the same [[Microorganism|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]]''.
* 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.{{ref|Wubbel}}
* In contrast, older children and teenagers are more likely to acquire ''[[mycoplasma pneumoniae]]'' and ''[[chlamydophila pneumoniae]]'' than adults.<ref name="pmid10048679">{{cite journal| author=Wubbel L, Muniz L, Ahmed A, Trujillo M, Carubelli C, McCoig C et al.| title=Etiology and treatment of community-acquired pneumonia in ambulatory children. | journal=Pediatr Infect Dis J | year= 1999 | volume= 18 | issue= 2 | pages= 98-104 | pmid=10048679 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=10048679  }} </ref>
* A unique cause of CAP in this group is ''[[chlamydia trachomatis]]'', which is acquired during birth but does not cause pneumonia until 2-4 weeks later.
* A unique cause of CAP in this group is ''[[chlamydia trachomatis]]'', which is acquired during [[birth]] but does not cause pneumonia until 2-4 weeks later.
* Common viruses include [[respiratory syncytial virus]] (RSV), [[metapneumovirus]], [[adenovirus]], [[parainfluenza]], [[influenza]], and [[rhinovirus]].
* Common viruses include [[respiratory syncytial virus]] (RSV), [[metapneumovirus]], [[adenovirus]], [[parainfluenza]], [[influenza]], and [[rhinovirus]].
* RSV in particular is a common source of illness and hospitalization.{{ref|Abzug}}
* [[Human respiratory syncytial virus|RSV]] in particular is a common source of illness and [[Hospital|hospitalization]].<ref name="pmid2177540">{{cite journal| author=Abzug MJ, Beam AC, Gyorkos EA, Levin MJ| title=Viral pneumonia in the first month of life. | journal=Pediatr Infect Dis J | year= 1990 | volume= 9 | issue= 12 | pages= 881-5 | pmid=2177540 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=2177540  }} </ref>
* 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.
* [[Fungus|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.
 
===Microbiological Etiology===
{| style="border: 0px; font-size: 85%; margin: 3px; width:700px;" align="center"
| valign="top" |
|+
! style="background: #4479BA; color:#FFF;  width: 250px;" | Typical Bacteria
! style="background: #4479BA; color:#FFF;  width: 250px;" | Atypical Bacteria
! style="background: #4479BA; color:#FFF;  width: 250px;" | Viruses
|-
| style="padding: 5px 5px; background: #F5F5F5;" |
# ''[[Streptococcus pneumoniae]]''
# ''[[Haemophilus influenzae]]''
# ''[[Staphylococcus aureus]]''
# ''[[Escherichia coli]]''
# ''[[Klebsiella pneumoniae]]''
# ''[[Pseudomonas aeruginosa]]''
| style="padding: 5px 5px; background: #F5F5F5;" |
# ''[[Mycoplasma pneumoniae]]''
# ''[[Chlamydophila pneumoniae]]''
# ''[[Legionella pneumophila]]''
| style="padding: 5px 5px; background: #F5F5F5;" |
# ''[[Influenza]]''
# ''[[Parainfluenza]]''
# ''[[Respiratory syncytial virus|Respiratory syncytial virus (RSV)]]''
# ''[[Metapneumovirus]]''
# ''[[Adenovirus]]''
|}
 
====Most Common Etiologies for Community-Acquired Pneumonia <small><ref name="pmid17278083">{{cite journal |author=Mandell LA, Wunderink RG, Anzueto A, Bartlett JG, Campbell GD, Dean NC, Dowell SF, File TM, Musher DM, Niederman MS, Torres A, Whitney CG |title=Infectious Diseases Society of America/American Thoracic Society consensus guidelines on the management of community-acquired pneumonia in adults |journal=[[Clinical Infectious Diseases : an Official Publication of the Infectious Diseases Society of America]] |volume=44 Suppl 2 |issue= |pages=S27–72 |year=2007 |month=March |pmid=17278083 |doi=10.1086/511159 |url=http://www.cid.oxfordjournals.org/cgi/pmidlookup?view=long&pmid=17278083 |accessdate=2012-09-06}}</ref><ref name="Wong-2013">{{Cite journal  | last1 = Wong | first1 = KK. | last2 = Fistek | first2 = M. | last3 = Watkins | first3 = RR. | title = Community-acquired pneumonia caused by Yersinia enterocolitica in an immunocompetent patient. | journal = J Med Microbiol | volume = 62 | issue = Pt 4 | pages = 650-1 | month = Apr | year = 2013 | doi = 10.1099/jmm.0.053488-0 | PMID = 23242642 }}</ref><ref name="Oh-2013">{{Cite journal  | last1 = Oh | first1 = YJ. | last2 = Song | first2 = SH. | last3 = Baik | first3 = SH. | last4 = Lee | first4 = HH. | last5 = Han | first5 = IM. | last6 = Oh | first6 = DH. | title = A case of fulminant community-acquired Acinetobacter baumannii pneumonia in Korea. | journal = Korean J Intern Med | volume = 28 | issue = 4 | pages = 486-90 | month = Jul | year = 2013 | doi = 10.3904/kjim.2013.28.4.486 | PMID = 23864808 }}</ref></small>====
{| style="border: 0px; font-size: 85%; margin: 3px; width:700px;" align="center"
| valign="top" |
|+
! style="background: #4479BA; color:#FFF;  width: 250px;" | Outpatient
 
! style="background: #4479BA; color:#FFF;  width: 250px;" | Inpatient (non-ICU)
 
! style="background: #4479BA; color:#FFF;  width: 250px;" | Inpatient (ICU)
 
|-
| style="padding: 5px 5px; background: #F5F5F5;" |
#[[Streptococcus pneumoniae]]
#[[Mycoplasma pneumoniae]]
#[[Haemophilus influenzae]]
#[[Chlamydophila pneumoniae]]
#[[Influenza|Influenza A and B]], [[adenovirus]], [[respiratory syncytial virus]], [[parainfluenza]]
| style="padding: 5px 5px; background: #F5F5F5;" |
#[[Streptococcus pneumoniae]]
#[[Mycoplasma pneumoniae]]
#[[Haemophilus influenzae]]
#[[Legionella]]
#[[Aspiration]]
#[[Influenza|Influenza A and B]], [[adenovirus]], [[respiratory syncytial virus]], [[parainfluenza]]
#[[Yersinia enterocolitica]]
| style="padding: 5px 5px; background: #F5F5F5;" |
#[[Streptococcus pneumoniae]]
#[[Staphylococcus aureus]]
#[[Legionella]]
#[[Gram-negative bacilli]]
#[[Haemophilus influenzae]]
#[[Acinetobacter baumannii]]
|}


===Adults===
==Community Acquired Pneumonia==
====Viruses====
 
* Viruses cause 20% of CAP cases.
===Most Common Etiologies for Community-Acquired Pneumonia <small><ref name="pmid17278083">{{cite journal |author=Mandell LA, Wunderink RG, Anzueto A, Bartlett JG, Campbell GD, Dean NC, Dowell SF, File TM, Musher DM, Niederman MS, Torres A, Whitney CG |title=Infectious Diseases Society of America/American Thoracic Society consensus guidelines on the management of community-acquired pneumonia in adults |journal=[[Clinical Infectious Diseases : an Official Publication of the Infectious Diseases Society of America]] |volume=44 Suppl 2 |issue= |pages=S27–72 |year=2007 |month=March |pmid=17278083 |doi=10.1086/511159 |url=http://www.cid.oxfordjournals.org/cgi/pmidlookup?view=long&pmid=17278083 |accessdate=2012-09-06}}</ref><ref name="Wong-2013">{{Cite journal  | last1 = Wong | first1 = KK. | last2 = Fistek | first2 = M. | last3 = Watkins | first3 = RR. | title = Community-acquired pneumonia caused by Yersinia enterocolitica in an immunocompetent patient. | journal = J Med Microbiol | volume = 62 | issue = Pt 4 | pages = 650-1 | month = Apr | year = 2013 | doi = 10.1099/jmm.0.053488-0 | PMID = 23242642 }}</ref><ref name="Oh-2013">{{Cite journal  | last1 = Oh | first1 = YJ. | last2 = Song | first2 = SH. | last3 = Baik | first3 = SH. | last4 = Lee | first4 = HH. | last5 = Han | first5 = IM. | last6 = Oh | first6 = DH. | title = A case of fulminant community-acquired Acinetobacter baumannii pneumonia in Korea. | journal = Korean J Intern Med | volume = 28 | issue = 4 | pages = 486-90 | month = Jul | year = 2013 | doi = 10.3904/kjim.2013.28.4.486 | PMID = 23864808 }}</ref></small>===
* Common viruses are [[influenza]], [[parainfluenza]], [[respiratory syncytial virus]], [[metapneumovirus]], and [[adenovirus]].
{| style="border: 0px; font-size: 85%; margin: 3px; width:700px;" align="center"
* Less common viruses include [[varicella|chicken pox]], [[SARS]], [[H5N1|avian flu]], and [[hantavirus]].{{ref|Roux}}
| valign="top" |
====Atypical organisms====
|+
*[[Mycoplasma pneumoniae]], [[chlamydophila pneumoniae]], and [[Legionella|legionella pneumophila]] are often grouped as atypical pneumonia. Community acquired pneumonia caused by these agents present insidiously, with a non-productive cough and prominent extra-pulmonary complaints, such as myalgias and diarrhea (lack the typical pneumonia symptoms of fever, cough, and sputum).
! style="background: #4479BA; color:#FFF;  width: 250px;" | Outpatient
* Mycoplasma pneumonia is often called is "walking pneumonia." It is transmitted via respiratory droplets and is common among healthy individuals in close contact with one another, such as dormitories or military barracks.
* Atypical organisms are more difficult to grow, respond to different antibiotics, and were discovered more recently than the typical bacteria discovered in the early [[twentieth century]].


====Streptococcus pneumoniae====
! style="background: #4479BA; color:#FFF;  width: 250px;" | Inpatient (non-ICU)
* '''Streptococcus pneumoniae''' is the most common cause of [[community acquired pneumonia]].
* Aspiration pneumonia is most commonly caused by anaerobic organisms.
* Prior to the development of antibiotics and vaccination, it was a leading cause of death.
* Traditionally, it was highly sensitive to [[penicillin]], but 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]], alcoholism, other severe underlying disease, or recent treatment with antibiotics should initially be treated with antibiotics effective against DRSP.{{ref|Ruhe}}


====Hemophilus influenzae====
! style="background: #4479BA; color:#FFF;  width: 250px;" | Inpatient (ICU)  
* 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.
====Enteric Gram negative bacteria====
* Involve colonic bacteria E.coli and K.pneumonia
* 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.
====Pseudomonas aeruginosa====
* Uncommon cause of CAP but is a particularly difficult bacteria to treat.
* Individuals who are malnourished, have [[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]].{{ref|Lieberman}}
====Special situations====
* Coccidioides are common in southwestern US.
* Anaerobic infection is common in alcoholics, nevertheless, pneumococcal pneumonia remains the most common cause of CAP in alcoholics too.
* [[Psittacosis]] (due to [[Chlamydophila psittaci]]) should be considered in the patient with exposure to birds or bird droppings.
* [[Anaerobes]] are common in patients with poor dental hygiene, and suspected large volume of aspiration.
* [[Streptococcus pneumonia]], [[H.influenza]], [[Moraxella catarrhalis]], and [[legionella]] species are the common causes of community acquired pneumonia in [[Chronic obstructive pulmonary disorders]] and [[Smokers]].
* [[S. pneumonia]], gram negative bacilli, [[H.influenza]], [[staphylococcus aureus]], anaerobes, and [[chlamydiae pneumonia]] are commoner in nursing home residents.
* [[S. pneumonia]], [[H.influenza]], and [[mycobacterium tuberculosis]] are common pathogens in early stages of HIV. Whereas, [[P.jiroveci]], [[histoplasma]], and [[cryptococcus]] are commonly seen in late stages HIV.
* In patients with structural lung disease such as [[bronchiectasis]] and [[cystic fibrosis]], [[pseudomonas aeruginosa]], [[Burkholderia cepacia]] (pseudomonas), and [[staphylococcus aureus]] are the common pathogens involved.
==Aspiration pneumonia causes==
* Incompetent [[swallowing]] mechanism, such as in neurological disease (a common cause being [[cerebrovascular accident|strokes]]) or while a person is [[Drunkenness|intoxicated]].
* [[Iatrogenic]] causes such as [[general anaesthesia]] for an [[Surgery|operation]] and patients are therefore instructed to be [[nil per os]] (NPO) for at least four hours before surgery.
* Whether aspiration pneumonia represents a true bacterial infection or a chemical inflammatory process remains the subject of significant controversy.
==Infectious Diseases Society of America/American Thoracic Society consensus statement on common etiologies of community-acquired pneumonia in adults. <ref name="pmid17278083">{{cite journal |author=Mandell LA, Wunderink RG, Anzueto A, Bartlett JG, Campbell GD, Dean NC, Dowell SF, File TM, Musher DM, Niederman MS, Torres A, Whitney CG |title=Infectious Diseases Society of America/American Thoracic Society consensus guidelines on the management of community-acquired pneumonia in adults |journal=[[Clinical Infectious Diseases : an Official Publication of the Infectious Diseases Society of America]] |volume=44 Suppl 2 |issue= |pages=S27–72 |year=2007 |month=March |pmid=17278083 |doi=10.1086/511159 |url=http://www.cid.oxfordjournals.org/cgi/pmidlookup?view=long&pmid=17278083 |accessdate=2012-09-06}}</ref> (DONOT EDIT)==
{{lquote|
===Outpatient===
* [[Streptococcus pneumoniae]]
* [[Mycoplasma pneumoniae]]
* [[Haemophilus influenzae]]
* [[Chlamydophila pneumoniae]]
* [[Respiratory viruses]]
===Inpatient (non-ICU)===
* S. pneumoniae
* M. pneumoniae
* C. pneumoniae
* H. influenzae
* Legionella species
* Aspiration
* Respiratory virusesa
===Inpatient (ICU)===
* S. pneumoniae
* Staphylococcus aureus
* Legionella species
* Gram-negative bacilli
* H. influenzae
}}<br />


|-
| style="padding: 5px 5px; background: #F5F5F5;" |
#[[Streptococcus pneumoniae]]
#[[Mycoplasma pneumoniae]]
#[[Haemophilus influenzae]]
#[[Chlamydophila pneumoniae]]
#[[Influenza|Influenza A and B]], [[adenovirus]], [[respiratory syncytial virus]], [[parainfluenza]]
| style="padding: 5px 5px; background: #F5F5F5;" |
#[[Streptococcus pneumoniae]]
#[[Mycoplasma pneumoniae]]
#[[Haemophilus influenzae]]
#[[Legionella]]
#[[Aspiration]]
#[[Influenza|Influenza A and B]], [[adenovirus]], [[respiratory syncytial virus]], [[parainfluenza]]
#[[Yersinia enterocolitica]]
| style="padding: 5px 5px; background: #F5F5F5;" |
#[[Streptococcus pneumoniae]]
#[[Staphylococcus aureus]]
#[[Legionella]]
#[[Gram-negative bacilli]]
#[[Haemophilus influenzae]]
#[[Acinetobacter baumannii]]
|}
===Common Causes by Age Group===
{| style="border: 0px; font-size: 85%; margin: 3px; width:700px;" align="center"
| valign="top" |
|+
! style="background: #4479BA; color:#FFF;  width: 100px;" | Age Group
! style="background: #4479BA; color:#FFF;  width: 250px;" | Neonates
! style="background: #4479BA; color:#FFF;  width: 250px;" | Children
! style="background: #4479BA; color:#FFF;  width: 250px;" | Adults
|-
| style="padding: 5px 5px; background: #DCDCDC;font-weight: bold" | Bacteria
| style="padding: 5px 5px; background: #F5F5F5;" |
# ''[[Listeria monocytogenes]]''
# ''[[Mycobacterium tuberculosis]]''
| style="padding: 5px 5px; background: #F5F5F5;" |
# ''[[Mycoplasma pneumoniae]]''
# ''[[Chlamydophila pneumoniae]]''
# ''[[Legionella pneumophila]]''
# ''[[Chlamydia trachomatis]]''
| style="padding: 5px 5px; background: #F5F5F5;" |
'''Typical Bacteria'''
# ''[[Streptococcus pneumoniae]]''
# ''[[Haemophilus influenzae]]''
# ''[[Escherichia coli]]''
# ''[[Klebsiella pneumoniae]]''
# ''[[Pseudomonas aeruginosa]]''
'''Atypical Bacteria'''
# ''[[Mycoplasma pneumoniae]]''
# ''[[Chlamydophila pneumoniae]]''
# ''[[Legionella pneumophila]]''
|-
| style="padding: 5px 5px; background: #DCDCDC;font-weight: bold" | Virus
| style="padding: 5px 5px; background: #F5F5F5;" |
# [[Herpes simplex virus]]
# [[Adenovirus]]
# [[Mumps]]
# [[Enterovirus]]
| style="padding: 5px 5px; background: #F5F5F5;" |
# [[Respiratory syncytial virus|Respiratory syncytial virus (RSV)]]
# [[Metapneumovirus]]
# [[Adenovirus]]
# [[Parainfluenza]]
# [[Influenza]]
# [[Rhinovirus]]
| style="padding: 5px 5px; background: #F5F5F5;" |
# [[Influenza]]
# [[Parainfluenza]]
# [[Respiratory syncytial virus|Respiratory syncytial virus (RSV)]]
# [[Metapneumovirus]]
# [[Adenovirus]]
|}


* Newborn [[infant]]s, [[children]], and [[adult]]s are at risk for different spectrums of disease causing microorganisms.


* In addition, adults with [[chronic (medicine)|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.


===Infants and Newborns===


* GBS causes at least 50% of cases of CAP in the first week of life.{{ref|Webber}}
* Other bacterial causes in the newborn period include ''[[Listeria monocytogenes]]'' and ''[[Mycobacterium tuberculosis]]''.
* Viral causes like [[herpes simplex virus]] (most common), [[adenovirus]], [[mumps]], and [[enterovirus]].


===Children===


* For the most part, children older than one month are at risk for the same microorganisms as adults.
* Children less than five years are much less likely to have pneumonia caused by ''[[Mycoplasma pneumoniae]]'', ''[[Chlamydophila pneumoniae]]'', or ''[[Legionella|Legionella pneumophila]]''.<ref name="Shachor-Meyouhas-2012">{{Cite journal  | last1 = Shachor-Meyouhas | first1 = Y. | last2 = Arad-Cohen | first2 = N. | last3 = Zaidman | first3 = I. | last4 = Gefen | first4 = A. | last5 = Kassis | first5 = I. | title = [Legionella pneumonia in a child with leukemia]. | journal = Harefuah | volume = 151 | issue = 8 | pages = 479-82, 496 | month = Aug | year = 2012 | doi =  | PMID = 23350295 }}</ref>
* In contrast, older children and teenagers are more likely to acquire ''[[Mycoplasma pneumoniae]]'' and ''[[Chlamydophila pneumoniae]]'' than adults.{{ref|Wubbel}}
* A unique cause of CAP in this group is ''[[Chlamydia trachomatis]]'', which is acquired during birth but does not cause pneumonia until 2-4 weeks later.
* Common viruses include [[respiratory syncytial virus|respiratory syncytial virus (RSV)]], [[metapneumovirus]], [[adenovirus]], [[parainfluenza]], [[influenza]], and [[rhinovirus]].
* [[RSV]] in particular is a common source of illness and [[Hospital|hospitalization]].{{ref|Abzug}}
* Fungi and parasites are not typically encountered in otherwise healthy [[Infant|infants]], though maternally-derived [[syphilis]] can be a cause of CAP in this age group.


===Adults===
The causes of CAP in adults are outlined in the following categories:
======Viruses======


* [[Virus|Viruses]] account for about 20% cases of CAP.
* Common viruses are [[influenza]], [[parainfluenza]], [[respiratory syncytial virus]], [[metapneumovirus]], and [[adenovirus]].
* Less common viruses include [[varicella|chicken pox]], [[SARS]], [[H5N1|avian flu]], and [[hantavirus]].{{ref|Roux}}


======''Streptococcus pneumoniae''======


* ''[[Streptococcus pneumoniae]]'' is the most common cause of community-acquired pneumonia.
* [[Aspiration pneumonia]] is most commonly caused by [[anaerobic]] organisms.
* Prior to the development of [[Antibiotic|antibiotics]] and [[vaccination]], it was a leading cause of death.
* Traditionally, it was highly sensitive to [[penicillin]], but during the 1970s resistance to multiple [[Antibiotic|antibiotics]] began to develop.
* Current strains of drug resistant ''[[Streptococcus pneumoniae]]'' (DRSP) are common, accounting for twenty percent of all [[streptococcal]] [[Infection|infections]].
* Risk factors for DRSP in adults include being older than 65, having exposure to children in day care, [[alcoholism]], other severe underlying disease, or recent treatment with [[Antibiotic|antibiotics]]; individuals exposed to these risk factors should initially be treated with [[Antibiotic|antibiotics]] effective against DRSP.{{ref|Ruhe}}


======Atypical Organisms======
* ''[[Mycoplasma pneumoniae]]'', ''[[Chlamydophila pneumoniae]]'', and ''[[Legionella|Legionella pneumophila]]'' are often grouped as atypical pneumonia. Community-acquired pneumonia caused by these agents present insidiously, with a non-productive [[cough]] and prominent extra-[[Lung|pulmonary]] complaints, such as [[myalgia]]s and [[diarrhea]] (lack the typical [[pneumonia]] symptoms of [[fever]], [[cough]], and [[sputum]]).


* ''[[Mycoplasma pneumoniae]]'' is often referred to as "walking pneumonia." It is transmitted via respiratory droplets and is common among healthy individuals in close contact with one another in settings such as dormitories or military barracks.


* Atypical organisms are more difficult to grow and respond to different [[Antibiotic|antibiotics]]; they were discovered more recently than the typical [[bacteria]] discovered in the early twentieth century.


======''Haemophilus influenzae''======


* ''[[Haemophilus influenzae]]'' used to be a 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 [[Virus|viral]] pneumonia.


======Enteric Gram-Negative Bacteria======


* Enteric bacteria such as ''[[Escherichia coli]]'' and ''[[Klebsiella pneumoniae]]'' may cause commnity-acquired penumonia.
* Risk factors in adults for infection include: living in a [[nursing home]], serious [[heart disease|heart]] and [[lung disease]], and recent [[antibiotic]] use; these individuals should initially be treated with [[Antibiotic|antibiotics]] effective against enteric [[Gram-negative bacteria]].


======''Pseudomonas aeruginosa''======


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


======Special Situations======


* [[Coccidioidomycosis|Coccidioides spp.]] are common in southwestern area of the United States.
* [[Anaerobic]] infection is common in alcoholics. [[Pneumococcal]] pneumonia remains the most common cause of CAP in alcoholics.
* [[Psittacosis]] (caused by ''[[Chlamydophila psittaci]]'') should be considered in the patient with exposure to birds or bird droppings.
* [[Anaerobes]] are common in patients with poor dental hygiene and a suspected large volume of aspiration.
* ''[[Streptococcus pneumoniae]]'', ''[[Haemophilus influenzae]]'', ''[[Moraxella catarrhalis]]'', and ''[[Legionella]]'' species are the common causes of community acquired pneumonia in those with chronic obstructive pulmonary disorders and smokers.
* ''[[Streptococcus pneumoniae]]'', [[Gram-negative bacilli]], ''[[Haemophilus influenzae]]'', ''[[Staphylococcus aureus]]'', [[anaerobe]]s, and ''[[Chlamydophila pneumoniae]]'' are more common in nursing home residents.
* ''[[Streptococcus pneumoniae]]'', ''[[Haemophilus influenzae]]'', and ''[[Mycobacterium tuberculosis]]'' are common pathogens in early stages of [[HIV]], whereas, ''[[Pneumocystis jiroveci]]'', ''[[Histoplasma]]'', and ''[[Cryptococcus]]'' are commonly seen in late stages [[HIV]].
* In patients with structural lung disease such as [[bronchiectasis]] and [[cystic fibrosis]], ''[[Pseudomonas aeruginosa]]'', ''[[Burkholderia cepacia]]'', and ''[[Staphylococcus aureus]]'' are the common pathogens involved.


======Aspiration Pneumonia======


* Incompetent [[swallowing]] mechanism, as can be found in neurological disease (a common cause being [[cerebrovascular accident|strokes]]) or while a person is [[Drunkenness|intoxicated]].
* [[Iatrogenic]] causes such as [[general anaesthesia]] for an [[Surgery|operation]]. Patients are therefore instructed to be [[nil per os]] (NPO) for at least four hours before surgery.
* Whether [[aspiration pneumonia]] represents a true bacterial infection or a chemical inflammatory process remains the subject of significant controversy.


==Hospital Acquired Pneumonia==
The causes of hospital acquired pneumonia are as follows:<ref name="pmid15699079">{{cite journal |author= |title=Guidelines for the management of adults with hospital-acquired, ventilator-associated, and healthcare-associated pneumonia |journal=[[American Journal of Respiratory and Critical Care Medicine]] |volume=171 |issue=4 |pages=388–416 |year=2005 |month=February |pmid=15699079 |doi=10.1164/rccm.200405-644ST |url=http://ajrccm.atsjournals.org/cgi/pmidlookup?view=long&pmid=15699079 |accessdate=2012-09-12}}</ref>


===Aerobic Gram Negative Pathogens===
* Commonly polymicrobial
* Common microbial agents include:
** [[Pseudomonas aeruginosa]]
** [[Escherichia coli]]
** [[Klebsiella pneumoniae]]
** [[Acinetobacter]]


===Gram-Positive Pathogens===
* [[Staphylococcus aureus]]
* [[Methicillin resistant staphylococcus aureus]] (common in patients with [[diabetes mellitus]], [[head trauma]], and in ICU)


===Elderly Population===
* S. aureus
* Enteric [[gram-negative]] rods
* [[Streptococcus]] pneumoniae
* [[Pseudomonas]]


===Ventilator-associated Pneumonia (VAP)===
*The microbiologic [[Flora (microbiology)|flora]] responsible for VAP is different from that of the more common [[community-acquired pneumonia]] (CAP). In particular, [[Virus|viruses]] and [[Fungus|fungi]] are uncommon causes in people who do not have underlying [[immunocompromise|immune deficiencies]].
*Though any microorganism that causes CAP can cause VAP, there are several [[bacteria]] which are particularly important causes of VAP because of their resistance to commonly used [[Antibiotic|antibiotics]]. These bacteria are referred to as [[multidrug resistance|multidrug resistant]] (MDR).
*VAP has been classified into either early-onset pneumonia (EOP), if pneumonia develops within 96 hours of the patient’s admission to an ICU or intubation for mechanical ventilation, and late-onset pneumonia (LOP), if pneumonia develops after 96 hours of the patient’s admission to an ICU or intubation for mechanical ventilation. <ref>{{cite web|url=http://www.cdc.gov/hicpac/pdf/guidelines/HApneu2003guidelines.pdf |title=CDC GUIDELINES FOR PREVENTING HEALTH-CARE-ASSOCIATED PNEUMONIA, 2003}}</ref>
* This categorization can be helpful to clinicians in initiating empiric antimicrobial therapy for cases of pneumonia, when the results of microbiologic diagnostic testing are not yet available.
* EOP has been associated usually with non-multi-antimicrobial-resistant microorganisms such as [[Escherichia coli]], [[Klebsiella]] spp., [[Proteus]] spp., [[S. pneumoniae]], [[H. influenzae]], and oxacillin-sensitive [[S. aureus]].
*On the other hand, LOP has been associated with [[Pseudomonas aeruginosa]], [[oxacillin-resistant S. aureus]], and [[Acinetobacter spp]] (strains that are usually multi-antibiotic-resistant).


The following is a list of the most MDR common pathogens associated with ventilator-associated pneumonia:
* ''[[Pseudomonas aeruginosa]]'' is the most common MDR [[gram-negative]] bacterium causing VAP. ''[[Pseudomonas]]'' has natural resistance to many antibiotics and has been known to acquire resistance to every antibiotic except for polymixin B. [[Drug resistance|Resistance]] is typically acquired through upregulation or [[Mutations|mutation]] of a variety of efflux pumps which pump antbiotics out of the cell. Resistance may also occur through loss of an outer membrane porin channel (OprD).
* ''[[Klebsiella pneumoniae]]'' has natural resistance to some [[Beta-lactam antibiotic|beta-lactam antibiotic]]s such as [[ampicillin]]. Resistance to [[cephalosporins]] and [[aztreonam]] may arise through [[Enzyme induction and inhibition|induction]] of a [[plasmid]]-based extended spectrum [[beta-lactamase]] (ESBL) or [[plasmid]]-based ampC-type [[enzyme]].
* ''[[Serratia marcescens]]'' has an ampC [[gene]] which can be induced by exposure to [[Antibiotic|antibiotics]] such as [[Cephalosporin|cephalosporins]]. Thus, culture sensitivities may initially indicate appropriate treatment which fails due to [[Bacteria|bacterial]] response.
* ''[[Enterobacter]]'' as a group also have an inducible ampC gene. [[Enterobacter]] may also develop [[Drug resistance|resistance]] by acquiring [[Plasmid|plasmids]].
* ''[[Citrobacter]]'' also has an inducible ampC gene.
* ''[[Stenotrophomonas maltophilia]]'' often colonizes people who have [[endotracheal tube]]s or [[tracheostomy|tracheostomies]] but can also cause pneumonia. It is often resistant to a wide array of [[Antibiotic|antibiotics]] but is usually sensitive to [[co-trimoxazole]].
* ''[[Acinetobacter]]'' are becoming more common and may be resistant to [[carbapenem]]s such as [[imipenem]] and [[meropenem]].
* ''[[Burkholderia cepacia]]'' is an important organism in people with [[cystic fibrosis]] and is often resistant to multiple [[Antibiotic|antibiotics]].
* ''[[Methicillin-resistant Staphylococcus aureus]]'' is an increasing cause of VAP. As many as fifty percent of ''[[Staphylococcus aureus]]'' isolates in the intensive care setting are resistant to [[methicillin]]. [[Drug resistance|Resistance]] is conferred by the mecA gene.


==Aspiration Pneumonia Causes==
* Incompetent [[swallowing]] mechanism, such as in neurological disease (a common cause being [[cerebrovascular accident|strokes]]) or while a person is [[Drunkenness|intoxicated]].
* [[Iatrogenic]] causes such as [[general anaesthesia]] for an [[Surgery|operation]]. Patients are therefore instructed to be [[nil per os]] (NPO) for at least four hours before surgery.
* Whether aspiration pneumonia represents a true [[Bacteria|bacterial]] [[infection]] or a chemical inflammatory process remains the subject of significant controversy.


===Drug Side Effect===
*[[Blinatumomab]]
*[[Belimumab]]
*[[Boceprevir]]
*[[Ceritinib]]
*[[Dornase Alfa]]
*[[Enfuvirtide]]
*[[ethanolamine oleate]]
*[[Felbamate]]
*[[Iloperidone]]
*[[interferon alfacon-1]]
*[[Pegylated interferon alfa-2b]]


===Causes in Aphabetical Order===
{{columns-list|4|
*[[Acebutolol]]
*[[Achalasia]]
*[[Achromobacter xylosoxidans]]
*[[Acinetobacter baumannii]]
*[[Actinomycosis]]
*[[Acute bronchitis]]
*[[Acute interstitial pneumonia]]
*[[Acute respiratory distress syndrome]]
*[[upper respiratory infection|Acute upper respiratory infection]]
*[[Acute viral nasopharyngitis (common cold)]]
*[[Adenovirus]]
*[[Adiaspiromycosis]]
*[[Agranulocytosis]]
*[[Aicardi syndrome]]
*[[Allergic bronchopulmonary aspergillosis]]
*[[Alzheimer disease ]]
*[[Amiodarone]]
*[[ammonia|Ammonia inhalation]]
*[[Anaerobes]]
*[[Anesthesia]]
*[[Anthrax]]
*[[Arnold-Chiari malformation]]
*[[Asbestosis]]
*[[Aspergillosis]]
*[[Aspergillus]]
*[[Aspiration]]
*[[Aspiration pneumonia]]
*[[Ataxia telangiectasia]]
*[[Atransferrinemia]]
*[[Atypical pneumonia]]
*[[aureobasidium pullulans|Aureobasidium pullulans exposure]]
*[[Austrian triad]]
*[[Avian influenza]]
*[[Bacillus anthracis]]
*[[Becker's muscular dystrophy]]
*[[Belimumab]]
*[[Blastomyces dermatitidis]]
*[[Blastomycosis]]
*[[Bleomycin]]
*[[Blinatumomab]]
*[[human bocavirus|Bocavirus]]
*[[Boceprevir]]
*[[Bordetella pertussis]]
*[[Bronchiectasis]]
*[[Bronchogenic carcinoma]]
*[[Brucella abortus]]
*[[Bucillamine]]
*[[Burkholderia cepacia]]
*[[Burkholderia pseudomallei]]
*[[Byssinosis]]
*[[Candida]]
*[[Captopril]]
*[[Carbamazepine]]
*[[Cerebrovascular accident]]
*[[Ceritinib]]
*[[Chediak-Higashi syndrome]]
*[[Chemical pneumonia]]
*[[Chicken pox]]
*[[Chlamydia trachomatis]]
*[[Chlamydophila pneumoniae]]
*[[Chlamydophila psittaci]]
*[[Chlorine gas]]
*[[Chloroacetophenone]]
*[[Cholesterol pneumonia]]
*[[Chronic granulomatous disease]]
*[[Chronic renal failure]]
*[[Cocaine abuse]]
*[[Coccidioides immitis]]
*[[Coccidioidomycosis]]
*[[Common cold]]
*[[Common variable immunodeficiency]]
*[[Community-acquired pneumonia]]
*[[Congenital pulmonary anomalies]]
*[[Cornelia de Lange syndrome]]
*[[Coronavirus]]
*[[Corticobasal degeneration]]
*[[Coxiella burnetii]]
*[[Crizotinib]]
*[[Cryptococcus neoformans]]
*[[Cryptogenic organizing pneumonia]]
*[[CS gas]]
*[[Cyclophosphamide]]
*[[Cystic fibrosis]]
*[[Cytomegalovirus]]
*[[Dermatomyositis]]
*[[Dihydroergocryptine]]
*[[Dihydroergotamine]]
*[[Docetaxel]]
*[[Dornase alfa]]
*[[Down syndrome]]
*[[Dressler syndrome]]
*[[Dronedarone]]
*[[Duchenne muscular dystrophy]]
*[[microsporidiosis pathophysiology|Encephalitozoon cuniculi infection]]
*[[Enfuvirtide]]
*[[Enterobacter]]
*[[Enterovirus]]
*[[Eosinophilic pneumonia]]
*[[Epiglottitis]]
*[[Escherichia coli]]
*[[Esophageal atresia]]
*[[Ethanolamine oleate]]
*[[Extrinsic allergic alveolitis]]
*[[Felbamate]]
*[[Flu]]
*[[formalin|Formalin vapors inhalation]]
*[[Francisella tularensis]]
*[[Gastric content aspiration]]
*[[Gastroesophageal reflux]]
*[[Gemcitabine]]
*[[General anaesthesia]]
*[[Gold]]
*[[Gold salts]]
*[[Gram-negative bacilli]]
*[[Group A streptococcal infection]]
*[[Group B streptococcal infection]]
*[[Haemophilus influenzae]]
*[[Hamman-Rich syndrome]]
*[[Hantavirus]]
*[[Herpes simplex virus]]
*[[Hexamethonium]]
*[[Histoplasma capsulatum]]
*[[Histoplasmosis]]
*[[HIV]]
*[[Hospital-acquired pneumonia]]
*[[Human T-lymphotropic virus]]
*[[hydrocarbon|Hydrocarbon poisoning]]
*[[Hydrogen sulfide]]
*[[Hyper-IgE syndrome]]
*[[Hyper-IgM syndrome]]
*[[Hypersensitivity pneumonitis]]
*[[Idelalisib]]
*[[myopathy|Idiopathic myopathy]]
*[[Idiopathic Parkinson's disease]]
*[[immunoglobulin G|IgG deficiency]]
*[[Iloperidone]]
*[[immunoglobulin G||Immunoglobulin G subclass deficiency]]
*[[dysphagia|Infantile dysphagia]]
*[[hypophosphatasia|Infantile hypophosphatasia]]
*[[Inflammatory bowel disease]]
*[[Influenza]]
*[[Interferon alfacon-1]]
*[[Interstitial lung disease]]
*[[Jeune's syndrome]]
*[[Kartagener syndrome]]
*[[Klebsiella]]
*[[Klebsiella pneumoniae]]
*[[Kyasanur-Forrest disease]]
*[[Larynx|Laryngeal cleft]]
*[[Legionella pneumophila]]
*[[Legionnaires' disease]]
*[[Lenz-Majewski hyperostotic dwarfism syndrome]]
*[[Leptospira]]
*[[Lipoid pneumonia]]
*[[Listeria monocytogenes]]
*[[Listeriosis]]
*[[Löffler's syndrome]]
*[[Lung abscess]]
*[[Lung cancer]]
*[[Lymphocytic interstitial pneumonia]]
*[[Machado-Joseph disease]]
*[[Malignancy]]
*[[Malignant buotonneuse fever]]
*[[spinocerebellar ataxia|Marie type ataxia]]
*[[Measles]]
*[[Mefloquine]]
*[[Melioidosis]]
*[[Mesalazine]]
*[[Metapneumovirus]]
*[[Methicillin-resistant staphylococcus aureus]]
*[[Methotrexate]]
*[[Middle East respiratory syndrome coronavirus infection]]
*[[Minocycline]]
*[[Mobius syndrome]]
*[[Moraxella catarrhalis]]
*[[MSSA]]
*[[Multiple myeloma]]
*[[popliteal pterygium syndrome|Multiple pterygium syndrome]]
*[[Mumps]]
*[[Mycobacterium avium-intracellulare]]
*[[Mycobacterium haemophilum]]
*[[Mycobacterium kansasii]]
*[[Mycobacterium tuberculosis]]
*[[Mycoplasma hominis]]
*[[Mycoplasma pneumoniae]]
*[[Neisseria meningitidis]]
*[[pneumonia|Neonatal pneumonia]]
*[[Neutropenia]]
*[[Nezelof syndrome]]
*[[Nilutamide]]
*[[Nitrofurantoin]]
*[[Nitrogen dioxide]]
*[[Nivolumab]]
*[[Nocardia]]
*[[Nocardiosis]]
*[[Occupational lung disease]]
*[[Olaparib]]
*[[Osteogenesis imperfecta]]
*[[ozone|Ozone inhalation]]
*[[Paclitaxel]]
*[[paracoccidioidomycosis|Paracoccidioides]]
*[[Paragonimiasis]]
*[[Parainfluenza]]
*[[Parechovirus]]
*[[Parkinson disease]]
*[[Pegylated interferon alfa-2b]]
*[[Pembrolizumab]]
*[[Penicillamine]]
*[[Persistent vegetative state]]
*[[Pertussis]]
*[[Phenytoin]]
*[[phosgene|Phosgene inhalation]]
*[[Pittsburgh pneumonia]]
*[[Plague]]
*[[Pleurisy]]
*[[Pneumococcal pneumonia]]
*[[Pneumococcus]]
*[[Pneumoconiosis]]
*[[Pneumocystis jiroveci]]
*[[Pneumocystis jirovecii pneumonia]]
*[[Pneumonic plague]]
*[[Polymyositis]]
*[[early myoclonic encephalopathy|Precocious myoclonic encephalopathy]]
*[[Progressive supranuclear palsy]]
*[[Proteus]]
*[[Pseudomonas aeruginosa]]
*[[pseudomonas|Pseudomonas pseudomallei]]
*[[Pseudophosphatasia]]
*[[Psittacosis]]
*[[Pulmonary surfactant-associated protein C]]
*[[Q fever]]
*[[Radiotherapy]]
*[[Rat-bite fever]]
*[[Respiratory syncytial virus]]
*[[Rheumatic fever]]
*[[Rheumatoid arthritis]]
*[[Rhinovirus]]
*[[Rhodococcus equi]]
*[[Rickettsia rickettsii]]
*[[Rituximab]]
*[[SCID]]
*[[Serratia]]
*[[Severe acute respiratory syndrome]]
*[[Sickle cell anemia]]
*[[Simpson-Golabi-Behmel syndrome]]
*[[Sjogren's syndrome]]
*[[Skeletal dysplasia]]
*[[Sporotrichosis]]
*[[Staphylococcus aureus]]
*[[Stenotrophomonas maltophilia]]
*[[pneumonitis|Sterile pneumonitis]]
*[[Still's disease]]
*[[Streptococcus agalactiae]]
*[[Streptococcus Group A]]
*[[Streptococcus pneumoniae]]
*[[sulfur dioxide|Sulfur dioxide inhalation]]
*[[Sulfasalazine]]
*[[Swine flu]]
*[[Systemic lupus erythematosus ]]
*[[Systemic sclerosis]]
*[[pneumoconiosis|Talc pneumoconiosis]]
*[[Ticlopidine]]
*[[Torulopsis]]
*[[Toxocariasis]]
*[[Toxoplasma gondii]]
*[[Trametinib]]
*[[Treponema pallidum]]
*[[Trichosporon]]
*[[Trypanosomiasis]]
*[[Tularemia]]
*[[Typhoid fever]]
*[[Typhus]]
*[[Ureaplasma urealyticum]]
*[[Usual interstitial pneumonia]]
*[[Varicella]]
*[[Varicella-zoster virus]]
*[[WHIM syndrome]]
*[[Whooping cough]]
*[[Williams-Campbell syndrome]]
*[[X-linked agammaglobulinemia]]
*[[Yersinia enterocolitica]]
*[[Yersinia pestis]]
*[[Zygomycosis]]
}}


===Causes by Organ System===


{| style="width:80%; height:100px" border="1"
| style="width:25%" bgcolor="LightSteelBlue" ; border="1" |'''Cardiovascular'''
| style="width:75%" bgcolor="Beige" ; border="1" | No underlying causes
|-
| bgcolor="LightSteelBlue" | '''Chemical/Poisoning'''
| bgcolor="Beige" | No underlying cause
|- bgcolor="LightSteelBlue"
| '''Dental'''
| bgcolor="Beige" | No underlying causes
|-
|- bgcolor="LightSteelBlue"
| '''Dermatologic'''
| bgcolor="Beige" | No underlying causes
|-
|- bgcolor="LightSteelBlue"
| '''Drug Side Effect'''
| bgcolor="Beige" |[[Blinatumomab]], [[belimumab]], [[boceprevir]], [[ceritinib]], [[dornase alfa]], [[enfuvirtide]], [[ethanolamine oleate]], [[felbamate]], [[iloperidone]], [[interferon alfacon-1]], [[pegylated interferon alfa-2b]]
|-
|- bgcolor="LightSteelBlue"
| '''Ear Nose Throat'''
| bgcolor="Beige" | No underlying causes
|-
|- bgcolor="LightSteelBlue"
| '''Endocrine'''
| bgcolor="Beige" | No underlying causes
|-
|- bgcolor="LightSteelBlue"
| '''Environmental'''
| bgcolor="Beige" | No underlying cause
|-
|- bgcolor="LightSteelBlue"
| '''Gastroenterologic'''
| bgcolor="Beige" | No underlying cause
|-
|- bgcolor="LightSteelBlue"
| '''Genetic'''
| bgcolor="Beige" | No underlying cause
|-
|- bgcolor="LightSteelBlue"
| '''Hematologic'''
| bgcolor="Beige" | No underlying causes
|-
|- bgcolor="LightSteelBlue"
| '''Iatrogenic'''
| bgcolor="Beige" | No underlying cause
|-
|- bgcolor="LightSteelBlue"
| '''Infectious Disease'''
| bgcolor="Beige" | [[Acinetobacter baumannii]], [[actinomycosis]], [[adenovirus|adenovirus (serotype 1, 2, 3, 4, 5, 7, 14, 21, 35)]], [[AIDS|AIDS-related opportunistic infections]], [[aspergillosis]], [[aspiration]], [[bacillus anthracis]], [[bird flu|bird flu (avian influenza)]], [[blastomycosis]], [[burkholderia cepacia]], [[burkholderia pseudomallei]], [[chlamydophila pneumoniae]], [[chickenpox]], [[coccidioides immitis]], [[coronavirus]], [[coxiella burnetii|coxiella burnetii (Q fever)]], [[cryptococcus neoformans]], [[cytomegalovirus]], [[escherichia coli]], [[enterovirus]], [[francisella tularensis]], [[gram-negative bacilli]], [[haemophilus influenzae]], H1N1 flu, [[hantavirus]], [[herpes simplex virus]], [[Histoplasma capsulatum]], [[histoplasmosis]], [[human bocavirus]], [[parechovirus|Human parechovirus types 1, 2, and 3]], [[influenza]], [[klebsiella pneumoniae]], [[legionella micdadei]], [[legionella pneumophila|legionella pneumophila (Legionnaires' disease)]], [[listeria monocytogenes]], [[mycoplasma pneumoniae]], [[measles]], [[melioidosis]], [[metapneumovirus]], [[Middle East respiratory syndrome coronavirus]], [[moraxella catarrhalis]], [[mumps]], [[mycobacterium avium-intracellulare]], [[mycobacterium haemophilum]], [[mycobacterium kansasii]], [[neisseria meningitidis]], [[coronavirus|New Haven coronavirus]], [[nocardia]], [[paragonimiasis]], [[parainfluenza]], [[pneumocystis jiroveci]], [[pneumonic plague]], [[proteus]], [[pseudomonas aeruginosa]], [[chlamydophila psittaci|chlamydophila psittaci (psittacosis)]], [[rat-bite fever]], [[respiratory syncytial virus|respiratory syncytial virus (RSV)]], [[rhinovirus]], [[rhodococcus equi]], [[streptococcus pneumoniae|streptococcus pneumoniae (pneumococcus)]], [[SARS]], [[serratia]], [[severe acute respiratory syndrome]], [[sporotrichosis ]] , [[staphylococcus aureus]], [[streptococcus agalactiae|streptococcus agalactiae (group B streptococcus)]], [[streptococcus pyogenes|streptococcus pyogenes (group A streptococcus)]], [[streptococcus pneumoniae]], [[swine flu]], [[toxocariasis ]] , [[toxoplasma gondii]], [[trichosporon ]] , [[trypanosomiasis]], [[typhus]], [[varicella-zoster virus]], [[yersinia enterocolitica]], [[yersinia pestis]], [[zygomycosis]]
|- bgcolor="LightSteelBlue"
| '''Musculoskeletal/Orthopedic'''
| bgcolor="Beige" | No underlying causes
|-
|- bgcolor="LightSteelBlue"
| '''Neurologic'''
| bgcolor="Beige" | No underlying causes
|-
|- bgcolor="LightSteelBlue"
| '''Nutritional/Metabolic'''
| bgcolor="Beige" | No underlying cause
|-
|- bgcolor="LightSteelBlue"
| '''Obstetric/Gynecologic'''
| bgcolor="Beige" | No underlying causes
|-
|- bgcolor="LightSteelBlue"
| '''Oncologic'''
| bgcolor="Beige" | No underlying cause
|- bgcolor="LightSteelBlue"
| '''Ophthalmologic'''
| bgcolor="Beige" | No underlying causes
|-
|- bgcolor="LightSteelBlue"
| '''Overdose/Toxicity'''
| bgcolor="Beige" | No underlying cause
|-
|- bgcolor="LightSteelBlue"
| '''Psychiatric'''
| bgcolor="Beige" | No underlying causes
|-
|- bgcolor="LightSteelBlue"
| '''Pulmonary'''
| bgcolor="Beige" | No underlying causes
|-
|- bgcolor="LightSteelBlue"
| '''Renal/Electrolyte'''
| bgcolor="Beige" | No underlying causes
|-
|- bgcolor="LightSteelBlue"
| '''Rheumatology/Immunology/Allergy'''
| bgcolor="Beige" | No underlying cause
|-
|- bgcolor="LightSteelBlue"
| '''Sexual'''
| bgcolor="Beige" | No underlying causes
|-
|- bgcolor="LightSteelBlue"
| '''Trauma'''
| bgcolor="Beige" | No underlying causes
|-
|- bgcolor="LightSteelBlue"
| '''Urologic'''
| bgcolor="Beige" | No underlying causes
|-
|- bgcolor="LightSteelBlue"
| '''Miscellaneous'''
| bgcolor="Beige" | No underlying cause
|-
|}


==References==
==References==
{{reflist|2}}
{{Reflist|2}}


[[Category:Disease]]
[[Category:Disease]]
[[Category:Pulmonology]]
[[Category:Pulmonology]]
[[Category:Infectious disease]]
 
[[Category:Pneumonia|Pneumonia]]
[[Category:Pneumonia|Pneumonia]]
[[Category:Emergency medicine]]
[[Category:Emergency medicine]]
[[Category:Crowdiagnosis]]


{{WH}}
{{WH}}
{{WS}}
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Latest revision as of 22:13, 5 March 2018

Pneumonia Microchapters

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Hamid Qazi, MD, BSc [2], Priyamvada Singh, M.D. [3]; Alejandro Lemor, M.D. [4]; Ogheneochuko Ajari, MB.BS, MS [5]

Overview

Pneumonia can result from a variety of causes, including infection with bacteria, viruses, fungi, parasites, and chemical or physical injury to the lungs. The etiology will depend upon various factors such as age, immune status, geographical area, and comorbidities.

Causes

Life Threatening Causes

Life-threatening causes include conditions which may result in death or permanent disability within 24 hours if left untreated.

Common Causes

Causes by Pathogen

Click here for bacterial pneumonia
Click here for viral pneumonia
Click here for fungal pneumonia

Infants

Source of Infection

Newborn

Children

Microbiological Etiology

Typical Bacteria Atypical Bacteria Viruses
  1. Streptococcus pneumoniae
  2. Haemophilus influenzae
  3. Staphylococcus aureus
  4. Escherichia coli
  5. Klebsiella pneumoniae
  6. Pseudomonas aeruginosa
  1. Mycoplasma pneumoniae
  2. Chlamydophila pneumoniae
  3. Legionella pneumophila
  1. Influenza
  2. Parainfluenza
  3. Respiratory syncytial virus (RSV)
  4. Metapneumovirus
  5. Adenovirus

Most Common Etiologies for Community-Acquired Pneumonia [4][5][6]

Outpatient Inpatient (non-ICU) Inpatient (ICU)
  1. Streptococcus pneumoniae
  2. Mycoplasma pneumoniae
  3. Haemophilus influenzae
  4. Chlamydophila pneumoniae
  5. Influenza A and B, adenovirus, respiratory syncytial virus, parainfluenza
  1. Streptococcus pneumoniae
  2. Mycoplasma pneumoniae
  3. Haemophilus influenzae
  4. Legionella
  5. Aspiration
  6. Influenza A and B, adenovirus, respiratory syncytial virus, parainfluenza
  7. Yersinia enterocolitica
  1. Streptococcus pneumoniae
  2. Staphylococcus aureus
  3. Legionella
  4. Gram-negative bacilli
  5. Haemophilus influenzae
  6. Acinetobacter baumannii

Community Acquired Pneumonia

Most Common Etiologies for Community-Acquired Pneumonia [4][5][6]

Outpatient Inpatient (non-ICU) Inpatient (ICU)
  1. Streptococcus pneumoniae
  2. Mycoplasma pneumoniae
  3. Haemophilus influenzae
  4. Chlamydophila pneumoniae
  5. Influenza A and B, adenovirus, respiratory syncytial virus, parainfluenza
  1. Streptococcus pneumoniae
  2. Mycoplasma pneumoniae
  3. Haemophilus influenzae
  4. Legionella
  5. Aspiration
  6. Influenza A and B, adenovirus, respiratory syncytial virus, parainfluenza
  7. Yersinia enterocolitica
  1. Streptococcus pneumoniae
  2. Staphylococcus aureus
  3. Legionella
  4. Gram-negative bacilli
  5. Haemophilus influenzae
  6. Acinetobacter baumannii

Common Causes by Age Group

Age Group Neonates Children Adults
Bacteria
  1. Listeria monocytogenes
  2. Mycobacterium tuberculosis
  1. Mycoplasma pneumoniae
  2. Chlamydophila pneumoniae
  3. Legionella pneumophila
  4. Chlamydia trachomatis

Typical Bacteria

  1. Streptococcus pneumoniae
  2. Haemophilus influenzae
  3. Escherichia coli
  4. Klebsiella pneumoniae
  5. Pseudomonas aeruginosa

Atypical Bacteria

  1. Mycoplasma pneumoniae
  2. Chlamydophila pneumoniae
  3. Legionella pneumophila
Virus
  1. Herpes simplex virus
  2. Adenovirus
  3. Mumps
  4. Enterovirus
  1. Respiratory syncytial virus (RSV)
  2. Metapneumovirus
  3. Adenovirus
  4. Parainfluenza
  5. Influenza
  6. Rhinovirus
  1. Influenza
  2. Parainfluenza
  3. Respiratory syncytial virus (RSV)
  4. Metapneumovirus
  5. Adenovirus
  • Newborn infants, children, and adults 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 homes, who have recently been treated with antibiotics, or who are alcoholics are at risk for unique infections.

Infants and Newborns

Children

Adults

The causes of CAP in adults are outlined in the following categories:

Viruses
Streptococcus pneumoniae
Atypical Organisms
  • Mycoplasma pneumoniae is often referred to as "walking pneumonia." It is transmitted via respiratory droplets and is common among healthy individuals in close contact with one another in settings such as dormitories or military barracks.
  • Atypical organisms are more difficult to grow and respond to different antibiotics; they were discovered more recently than the typical bacteria discovered in the early twentieth century.
Haemophilus influenzae
  • Haemophilus influenzae used to be a 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.
Enteric Gram-Negative Bacteria
Pseudomonas aeruginosa
Special Situations
Aspiration Pneumonia

Hospital Acquired Pneumonia

The causes of hospital acquired pneumonia are as follows:[8]

Aerobic Gram Negative Pathogens

Gram-Positive Pathogens

Elderly Population

Ventilator-associated Pneumonia (VAP)

  • The microbiologic flora responsible for VAP is different from that of the more common community-acquired pneumonia (CAP). In particular, viruses and fungi are uncommon causes in people who do not have underlying immune deficiencies.
  • Though any microorganism that causes CAP can cause VAP, there are several bacteria which are particularly important causes of VAP because of their resistance to commonly used antibiotics. These bacteria are referred to as multidrug resistant (MDR).
  • VAP has been classified into either early-onset pneumonia (EOP), if pneumonia develops within 96 hours of the patient’s admission to an ICU or intubation for mechanical ventilation, and late-onset pneumonia (LOP), if pneumonia develops after 96 hours of the patient’s admission to an ICU or intubation for mechanical ventilation. [9]
  • This categorization can be helpful to clinicians in initiating empiric antimicrobial therapy for cases of pneumonia, when the results of microbiologic diagnostic testing are not yet available.
  • EOP has been associated usually with non-multi-antimicrobial-resistant microorganisms such as Escherichia coli, Klebsiella spp., Proteus spp., S. pneumoniae, H. influenzae, and oxacillin-sensitive S. aureus.
  • On the other hand, LOP has been associated with Pseudomonas aeruginosa, oxacillin-resistant S. aureus, and Acinetobacter spp (strains that are usually multi-antibiotic-resistant).

The following is a list of the most MDR common pathogens associated with ventilator-associated pneumonia:

Aspiration Pneumonia Causes

Drug Side Effect

Causes in Aphabetical Order

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4

Causes by Organ System

Cardiovascular No underlying causes
Chemical/Poisoning No underlying cause
Dental No underlying causes
Dermatologic No underlying causes
Drug Side Effect Blinatumomab, belimumab, boceprevir, ceritinib, dornase alfa, enfuvirtide, ethanolamine oleate, felbamate, iloperidone, interferon alfacon-1, pegylated interferon alfa-2b
Ear Nose Throat No underlying causes
Endocrine No underlying causes
Environmental No underlying cause
Gastroenterologic No underlying cause
Genetic No underlying cause
Hematologic No underlying causes
Iatrogenic No underlying cause
Infectious Disease Acinetobacter baumannii, actinomycosis, adenovirus (serotype 1, 2, 3, 4, 5, 7, 14, 21, 35), AIDS-related opportunistic infections, aspergillosis, aspiration, bacillus anthracis, bird flu (avian influenza), blastomycosis, burkholderia cepacia, burkholderia pseudomallei, chlamydophila pneumoniae, chickenpox, coccidioides immitis, coronavirus, coxiella burnetii (Q fever), cryptococcus neoformans, cytomegalovirus, escherichia coli, enterovirus, francisella tularensis, gram-negative bacilli, haemophilus influenzae, H1N1 flu, hantavirus, herpes simplex virus, Histoplasma capsulatum, histoplasmosis, human bocavirus, Human parechovirus types 1, 2, and 3, influenza, klebsiella pneumoniae, legionella micdadei, legionella pneumophila (Legionnaires' disease), listeria monocytogenes, mycoplasma pneumoniae, measles, melioidosis, metapneumovirus, Middle East respiratory syndrome coronavirus, moraxella catarrhalis, mumps, mycobacterium avium-intracellulare, mycobacterium haemophilum, mycobacterium kansasii, neisseria meningitidis, New Haven coronavirus, nocardia, paragonimiasis, parainfluenza, pneumocystis jiroveci, pneumonic plague, proteus, pseudomonas aeruginosa, chlamydophila psittaci (psittacosis), rat-bite fever, respiratory syncytial virus (RSV), rhinovirus, rhodococcus equi, streptococcus pneumoniae (pneumococcus), SARS, serratia, severe acute respiratory syndrome, sporotrichosis , staphylococcus aureus, streptococcus agalactiae (group B streptococcus), streptococcus pyogenes (group A streptococcus), streptococcus pneumoniae, swine flu, toxocariasis , toxoplasma gondii, trichosporon , trypanosomiasis, typhus, varicella-zoster virus, yersinia enterocolitica, yersinia pestis, zygomycosis
Musculoskeletal/Orthopedic No underlying causes
Neurologic No underlying causes
Nutritional/Metabolic No underlying cause
Obstetric/Gynecologic No underlying causes
Oncologic No underlying cause
Ophthalmologic No underlying causes
Overdose/Toxicity No underlying cause
Psychiatric No underlying causes
Pulmonary No underlying causes
Renal/Electrolyte No underlying causes
Rheumatology/Immunology/Allergy No underlying cause
Sexual No underlying causes
Trauma No underlying causes
Urologic No underlying causes
Miscellaneous No underlying cause

References

  1. Webber S, Wilkinson AR, Lindsell D, Hope PL, Dobson SR, Isaacs D (1990). "Neonatal pneumonia". Arch Dis Child. 65 (2): 207–11. PMC 1792235. PMID 2107797.
  2. Wubbel L, Muniz L, Ahmed A, Trujillo M, Carubelli C, McCoig C; et al. (1999). "Etiology and treatment of community-acquired pneumonia in ambulatory children". Pediatr Infect Dis J. 18 (2): 98–104. PMID 10048679.
  3. Abzug MJ, Beam AC, Gyorkos EA, Levin MJ (1990). "Viral pneumonia in the first month of life". Pediatr Infect Dis J. 9 (12): 881–5. PMID 2177540.
  4. 4.0 4.1 Mandell LA, Wunderink RG, Anzueto A, Bartlett JG, Campbell GD, Dean NC, Dowell SF, File TM, Musher DM, Niederman MS, Torres A, Whitney CG (2007). "Infectious Diseases Society of America/American Thoracic Society consensus guidelines on the management of community-acquired pneumonia in adults". Clinical Infectious Diseases : an Official Publication of the Infectious Diseases Society of America. 44 Suppl 2: S27–72. doi:10.1086/511159. PMID 17278083. Retrieved 2012-09-06. Unknown parameter |month= ignored (help)
  5. 5.0 5.1 Wong, KK.; Fistek, M.; Watkins, RR. (2013). "Community-acquired pneumonia caused by Yersinia enterocolitica in an immunocompetent patient". J Med Microbiol. 62 (Pt 4): 650–1. doi:10.1099/jmm.0.053488-0. PMID 23242642. Unknown parameter |month= ignored (help)
  6. 6.0 6.1 Oh, YJ.; Song, SH.; Baik, SH.; Lee, HH.; Han, IM.; Oh, DH. (2013). "A case of fulminant community-acquired Acinetobacter baumannii pneumonia in Korea". Korean J Intern Med. 28 (4): 486–90. doi:10.3904/kjim.2013.28.4.486. PMID 23864808. Unknown parameter |month= ignored (help)
  7. Shachor-Meyouhas, Y.; Arad-Cohen, N.; Zaidman, I.; Gefen, A.; Kassis, I. (2012). "[Legionella pneumonia in a child with leukemia]". Harefuah. 151 (8): 479–82, 496. PMID 23350295. Unknown parameter |month= ignored (help)
  8. "Guidelines for the management of adults with hospital-acquired, ventilator-associated, and healthcare-associated pneumonia". American Journal of Respiratory and Critical Care Medicine. 171 (4): 388–416. 2005. doi:10.1164/rccm.200405-644ST. PMID 15699079. Retrieved 2012-09-12. Unknown parameter |month= ignored (help)
  9. "CDC GUIDELINES FOR PREVENTING HEALTH-CARE-ASSOCIATED PNEUMONIA, 2003" (PDF).

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