Editing Pneumonia (section)

==Diagnosis==
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Pneumonia is typically diagnosed based on a combination of physical signs and often a [[chest X-ray]].<ref name=Diag10>{{cite journal | vauthors = Lynch T, Bialy L, Kellner JD, Osmond MH, Klassen TP, Durec T, Leicht R, Johnson DW | title = A systematic review on the diagnosis of pediatric bacterial pneumonia: when gold is bronze | journal = PLOS ONE| volume = 5 | issue = 8 | pages = e11989 | date = August 2010 | pmid = 20700510 | pmc = 2917358 | doi = 10.1371/journal.pone.0011989 | editor1-last = Huicho | bibcode = 2010PLoSO...511989L | editor1-first = Luis | doi-access = free }}</ref> In recent years, however, the role of lung ultrasonography has gained prominence, with substantial evidence demonstrating that, in expert hands, it surpasses radiography in accuracy.<ref>{{Cite journal |last1=Di Bella |first1=Stefano |last2=Sisto |first2=Ugo Giulio |last3=Mearelli |first3=Filippo |date=2025-01-09 |title=Community-Acquired Pneumonia |url=https://jamanetwork.com/journals/jama/fullarticle/2829043 |journal=JAMA |volume=333 |issue=6 |pages=535–536 |language=en |doi=10.1001/jama.2024.24962 |pmid=39786767 |issn=0098-7484}}</ref> In adults with normal vital signs and a normal lung examination, the diagnosis is unlikely.<ref>{{cite journal | vauthors = Marchello CS, Ebell MH, Dale AP, Harvill ET, Shen Y, Whalen CC | title = Signs and Symptoms That Rule out Community-Acquired Pneumonia in Outpatient Adults: A Systematic Review and Meta-Analysis | journal = Journal of the American Board of Family Medicine | volume = 32 | issue = 2 | pages = 234–47 | date = 2019 | pmid = 30850460 | pmc = 7422644 | doi = 10.3122/jabfm.2019.02.180219 | doi-access = free }}</ref> However, the underlying cause can be difficult to confirm, as there is no definitive test able to distinguish between bacterial and non-bacterial cause.<ref name=Lancet11/><ref name=Diag10/> The overall impression of a physician appears to be at least as good as decision rules for making or excluding the diagnosis.<ref>{{cite journal | vauthors = Dale AP, Marchello C, Ebell MH | title = Clinical gestalt to diagnose pneumonia, sinusitis, and pharyngitis: a meta-analysis | journal = The British Journal of General Practice | volume = 69 | issue = 684 | pages = e444–e453 | date = July 2019 | pmid = 31208974 | pmc = 6582453 | doi = 10.3399/bjgp19X704297 }}</ref>

===Diagnosis in children===
The [[World Health Organization]] has defined pneumonia in children clinically based on either a cough or difficulty breathing and a rapid respiratory rate, chest indrawing, or a decreased level of consciousness.<ref name=WHOBook/> A rapid respiratory rate is defined as greater than 60 breaths per minute in children under 2 months old, greater than 50 breaths per minute in children 2 months to 1 year old, or greater than 40 breaths per minute in children 1 to 5 years old.<ref name=WHOBook>{{cite book|last1=Ezzati|first1=Majid | last2 = Lopez | first2 = Alan D. | last3 = Rodgers | first3 = Anthony | last4 = Murray | first4 = Christopher J.L. |title=Comparative quantification of health risks|year=2004|publisher=World Health Organization|location=Genève|isbn=978-92-4-158031-1|page=70|url=https://books.google.com/books?id=ACV1jEGx4AgC&pg=PA70}}</ref>

In children, low oxygen levels and lower chest indrawing are more [[Sensitivity and specificity|sensitive]] than hearing chest [[crackles]] with a [[stethoscope]] or increased respiratory rate.<ref>{{cite journal | vauthors = Shah SN, Bachur RG, Simel DL, Neuman MI | title = Does This Child Have Pneumonia?: The Rational Clinical Examination Systematic Review | journal = JAMA | volume = 318 | issue = 5 | pages = 462–71 | date = August 2017 | pmid = 28763554 | doi = 10.1001/jama.2017.9039 | s2cid = 44974175 }}</ref> Grunting and nasal flaring may be other useful signs in children less than five years old.<ref>{{cite journal | vauthors = Rambaud-Althaus C, Althaus F, Genton B, D'Acremont V | title = Clinical features for diagnosis of pneumonia in children younger than 5 years: a systematic review and meta-analysis | journal = The Lancet. Infectious Diseases | volume = 15 | issue = 4 | pages = 439–50 | date = April 2015 | pmid = 25769269 | doi = 10.1016/s1473-3099(15)70017-4 }}</ref>

Lack of wheezing is an indicator of ''Mycoplasma pneumoniae'' in children with pneumonia, but as an indicator it is not accurate enough to decide whether or not [[macrolide]] treatment should be used.<ref name=Wang2012>{{cite journal | vauthors = Wang K, Gill P, Perera R, Thomson A, Mant D, Harnden A | title =  Clinical symptoms and signs for the diagnosis of ''Mycoplasma pneumoniae'' in children and adolescents with community-acquired pneumonia| journal = The Cochrane Database of Systematic Reviews | volume = 2012 | pages = CD009175 | date = October 2012 | issue = 10 | pmid = 23076954 | pmc = 7117561 | doi = 10.1002/14651858.CD009175.pub2 }}</ref> The presence of chest pain in children with pneumonia doubles the probability of ''Mycoplasma pneumoniae''.<ref name=Wang2012/>

===Diagnosis in adults===
In general, in adults, investigations are not needed in mild cases.<ref name=BTS09/> There is a very low risk of pneumonia if all [[vital sign]]s and [[chest auscultation|auscultation]] are normal.<ref>{{cite journal | vauthors = Saldías F, Méndez JI, Ramírez D, Díaz O | title = [Predictive value of history and physical examination for the diagnosis of community-acquired pneumonia in adults: a literature review] | journal = Revista Médica de Chile | volume = 135 | issue = 4 | pages = 517–28 | date = April 2007 | pmid = 17554463 | doi = 10.4067/s0034-98872007000400016 | doi-access = free }}</ref> [[C-reactive protein]] (CRP) may help support the diagnosis.<ref>{{cite journal | vauthors = Ebell MH, Bentivegna M, Cai X, Hulme C, Kearney M | title = Accuracy of Biomarkers for the Diagnosis of Adult Community-acquired Pneumonia: A Meta-analysis | journal = Academic Emergency Medicine | volume = 27 | issue = 3 | pages = 195–206 | date = March 2020 | pmid = 32100377 | doi = 10.1111/acem.13889 | s2cid = 211523779 | doi-access = free }}</ref> For those with CRP less than 20&nbsp;mg/L without convincing evidence of pneumonia, antibiotics are not recommended.<ref name="Elena 2015"/>

[[Procalcitonin]] may help determine the cause and support decisions about who should receive antibiotics.<ref name="pmid29037960">{{cite journal | vauthors = Schuetz P, Wirz Y, Sager R, Christ-Crain M, Stolz D, Tamm M, Bouadma L, Luyt CE, Wolff M, Chastre J, Tubach F, Kristoffersen KB, Burkhardt O, Welte T, Schroeder S, Nobre V, Wei L, Bucher HC, Annane D, Reinhart K, Falsey AR, Branche A, Damas P, Nijsten M, de Lange DW, Deliberato RO, Oliveira CF, Maravić-Stojković V, Verduri A, Beghé B, Cao B, Shehabi Y, Jensen JS, Corti C, van Oers JA, Beishuizen A, Girbes AR, de Jong E, Briel M, Mueller B | title = Effect of procalcitonin-guided antibiotic treatment on mortality in acute respiratory infections: a patient level meta-analysis | journal = The Lancet. Infectious Diseases | volume = 18 | issue = 1 | pages = 95–107 | date = January 2018 | pmid = 29037960 | doi = 10.1016/S1473-3099(17)30592-3 | doi-access = free | hdl = 1843/42632 | hdl-access = free }}</ref> Antibiotics are encouraged if the procalcitonin level reaches 0.25 μg/L, strongly encouraged if it reaches 0.5 μg/L, and strongly discouraged if the level is below 0.10 μg/L.<ref name="Elena 2015"/> In people requiring hospitalization, [[pulse oximetry]], [[chest radiography]] and [[blood test]]s – including a [[complete blood count]], [[serum electrolytes]], C-reactive protein level, and possibly [[liver function tests]] – are recommended.<ref name=BTS09/>

The diagnosis of [[influenza-like illness]] can be made based on the signs and symptoms; however, confirmation of an influenza infection requires testing.<ref name=ILI05>{{cite journal | vauthors = Call SA, Vollenweider MA, Hornung CA, Simel DL, McKinney WP | title = Does this patient have influenza? | journal = JAMA | volume = 293 | issue = 8 | pages = 987–97 | date = February 2005 | pmid = 15728170 | doi = 10.1001/jama.293.8.987 }}</ref> Thus, treatment is frequently based on the presence of influenza in the community or a [[Rapid influenza diagnostic test|rapid influenza test]].<ref name=ILI05/>

Adults 65 years old or older, as well as cigarette smokers and people with ongoing medical conditions are at increased risk for pneumonia.<ref>{{cite web |date=30 September 2022 |title=Risk Factors for Pneumonia|url=https://www.cdc.gov/pneumonia/riskfactors.html |access-date=16 January 2023 |website=CDC |language=en-us}}</ref>

===Physical exam===
[[Physical examination]] may sometimes reveal [[hypotension|low blood pressure]], [[tachycardia|high heart rate]], or low [[Oxygenation (medical)|oxygen saturation]].<ref name=Clinic2011/> The respiratory rate may be faster than normal, and this may occur a day or two before other signs.<ref name=Clinic2011/><ref name=M32/> Examination of the chest may be normal, but it may show decreased expansion on the affected side. Harsh breath sounds from the larger airways that are transmitted through the inflamed lung are termed [[bronchus|bronchial]] breathing and are heard on auscultation with a stethoscope.<ref name=Clinic2011/> Crackles (rales) may be heard over the affected area during [[inhalation|inspiration]].<ref name=Clinic2011/> [[Percussion (medicine)|Percussion]] may be dulled over the affected lung, and increased, rather than decreased, [[vocal resonation|vocal resonance]] distinguishes pneumonia from a [[pleural effusion]].<ref name=BMJ06/>

===Imaging===
[[File:X-ray of lobar pneumonia.jpg|thumb|A chest X-ray showing a very prominent wedge-shaped area of airspace consolidation in the right lung characteristic of acute bacterial lobar pneumonia]]
[[File:CT scan of the chest, demonstrating right-sided pneumonia.jpg|thumb|alt=A black-and-white image shows the internal organs in cross-section as generated by CT. Where one would expect black on the left, one sees a whiter area with black sticks through it.|CT of the chest demonstrating right-sided pneumonia (left side of the image)]]
A [[chest radiograph]] is frequently used in diagnosis.<ref name=Develop11/> In people with mild disease, imaging is needed only in those with potential complications, those not having improved with treatment, or those in which the cause is uncertain.<ref name=Develop11/><ref name=BTS09>{{cite journal | vauthors = Lim WS, Baudouin SV, George RC, Hill AT, Jamieson C, Le Jeune I, Macfarlane JT, Read RC, Roberts HJ, Levy ML, Wani M, Woodhead MA | title = BTS guidelines for the management of community acquired pneumonia in adults: update 2009 | journal = Thorax | volume = 64 | issue = Suppl 3 | pages = iii, 1–55 | date = October 2009 | pmid = 19783532 | doi = 10.1136/thx.2009.121434 | doi-access = free }}</ref> If a person is sufficiently sick to require hospitalization, a chest radiograph is recommended.<ref name=BTS09/> Findings do not always match the severity of disease and do not reliably separate between bacterial and viral infection.<ref name=Develop11/>

X-ray presentations of pneumonia may be classified as [[lobar pneumonia]], [[bronchopneumonia]], [[lobular pneumonia]], and [[interstitial pneumonia]].<ref>{{cite book | editor-last1 = Helms | editor-first1 = Clyde A. | editor-last2=Brant | editor-first2 = William E. | title = Fundamentals of diagnostic radiology | publisher = Wolters Kluwer/Lippincott Williams & Wilkins | location=Philadelphia | isbn=978-1-60831-911-4 | page=435 | url=https://books.google.com/books?id=o_4eoeOinNgC&pg=PA435 | edition=4th | date=20 March 2012}}</ref> Bacterial, community-acquired pneumonia classically show [[lung consolidation]] of one [[Bronchopulmonary segment|lung segmental lobe]], which is known as lobar pneumonia.<ref name=Rad07/> However, findings may vary, and other patterns are common in other types of pneumonia.<ref name=Rad07/> Aspiration pneumonia may present with bilateral opacities primarily in the bases of the lungs and on the right side.<ref name=Rad07/> Radiographs of viral pneumonia may appear normal, appear hyper-inflated, have bilateral patchy areas, or present similar to bacterial pneumonia with lobar consolidation.<ref name=Rad07/> Radiologic findings may not be present in the early stages of the disease, especially in the presence of dehydration, or may be difficult to interpret in the [[obesity|obese]] or those with a history of lung disease.<ref name=Clinic2011/> Complications such as pleural effusion may also be found on chest radiographs. Laterolateral chest radiographs can increase the diagnostic accuracy of lung consolidation and pleural effusion.<ref name="Elena 2015"/>

A [[CT scan]] can give additional information in indeterminate cases<ref name=Rad07/> and provide more details in those with an unclear chest radiograph (for example occult pneumonia in chronic obstructive pulmonary disease). They can be used to exclude [[pulmonary embolism]] and [[fungal pneumonia]], and detect lung abscesses in those who are not responding to treatments.<ref name="Elena 2015"/> However, CT scans are more expensive, have a higher dose of radiation, and cannot be done at bedside.<ref name="Elena 2015"/>

[[Lung ultrasound]] may also be useful in helping to make the diagnosis.<ref>{{cite journal |vauthors=Llamas-Álvarez AM, Tenza-Lozano EM, Latour-Pérez J |date=February 2017 |title=Accuracy of Lung Ultrasonography in the Diagnosis of Pneumonia in Adults: Systematic Review and Meta-Analysis |url=https://journal.chestnet.org/article/S0012-3692(16)62327-9/fulltext |journal=Chest |volume=151 |issue=2 |pages=374–82 |doi=10.1016/j.chest.2016.10.039 |pmid=27818332 |s2cid=24399240}}</ref> Ultrasound is radiation free and can be done at bedside. However, ultrasound requires specific skills to operate the machine and interpret the findings.<ref name="Elena 2015"/> It may be more accurate than chest X-ray.<ref>{{cite journal | vauthors = Ye X, Xiao H, Chen B, Zhang S | title = Accuracy of Lung Ultrasonography versus Chest Radiography for the Diagnosis of Adult Community-Acquired Pneumonia: Review of the Literature and Meta-Analysis | journal = PLOS ONE| volume = 10 | issue = 6 | pages = e0130066 | date = 2015 | pmid = 26107512 | pmc = 4479467 | doi = 10.1371/journal.pone.0130066 | bibcode = 2015PLoSO..1030066Y | doi-access = free }}</ref>

<gallery>
File:UOTW 34 - Ultrasound of the Week 1.webm|Pneumonia seen by ultrasound<ref name=UOTW34>{{cite web|title=UOTW No. 34 – Ultrasound of the Week|url=https://www.ultrasoundoftheweek.com/uotw-34/|website=Ultrasound of the Week|access-date=27 May 2017|date=20 January 2015|url-status=live|archive-url=https://web.archive.org/web/20170509114431/https://www.ultrasoundoftheweek.com/uotw-34/|archive-date=9 May 2017}}</ref>
File:UOTW 34 - Ultrasound of the Week 2.webm|Pneumonia seen by ultrasound<ref name=UOTW34/>
File:UOTW 34 - Ultrasound of the Week 3.jpg|Pneumonia seen by ultrasound<ref name=UOTW34/>
File:RtPneuKidMark.png|Right middle lobe pneumonia in a child as seen on plain X-ray
</gallery>

===Microbiology===
In people managed in the community, determining the causative agent is not cost-effective and typically does not alter management.<ref name=Develop11/> For people who do not respond to treatment, [[sputum culture]] should be considered, and culture for ''Mycobacterium tuberculosis'' should be carried out in persons with a chronic productive cough.<ref name=BTS09/> Microbiological evaluation is also indicated in severe pneumonia, alcoholism, [[asplenia]], immunosuppression, HIV infection, and those being empirically treated for MRSA of pseudomonas.<ref name="Elena 2015"/><ref name=Met2019>{{cite journal | vauthors = Metlay JP, Waterer GW, Long AC, Anzueto A, Brozek J, Crothers K, Cooley LA, Dean NC, Fine MJ, Flanders SA, Griffin MR, Metersky ML, Musher DM, Restrepo MI, Whitney CG | title = Diagnosis and Treatment of Adults with Community-acquired Pneumonia. An Official Clinical Practice Guideline of the American Thoracic Society and Infectious Diseases Society of America | journal = American Journal of Respiratory and Critical Care Medicine | volume = 200 | issue = 7 | pages = e45–e67 | date = October 2019 | pmid = 31573350 | pmc = 6812437 | doi = 10.1164/rccm.201908-1581ST }}</ref> Although positive [[blood culture]] and [[pleural fluid]] culture definitively establish the diagnosis of the type of micro-organism involved, a positive sputum culture has to be interpreted with care for the possibility of [[colonisation (biology)|colonisation]] of respiratory tract.<ref name="Elena 2015"/> Testing for other specific organisms may be recommended during outbreaks, for public health reasons.<ref name=BTS09/> In those hospitalized for severe disease, both sputum and [[blood cultures]] are recommended,<ref name=BTS09/> as well as testing the urine for [[antigen]]s to ''Legionella'' and ''Streptococcus''.<ref name=IDSA2007/> Viral infections, can be confirmed via detection of either the virus or its antigens with [[Viral culture|culture]] or [[polymerase chain reaction]] (PCR), among other techniques.<ref name=Lancet11/> ''Mycoplasma'', ''Legionella'', ''Streptococcus'', and ''Chlamydia'' can also be detected using PCR techniques on [[bronchoalveolar lavage]] and [[nasopharyngeal swab]].<ref name="Elena 2015"/> The causative agent is determined in only 15% of cases with routine microbiological tests.<ref name=BMJ06/>

===Classification===
{{Main|Classification of pneumonia}}
''Pneumonitis'' refers to lung inflammation; pneumonia refers to pneumonitis, usually due to infection but sometimes non-infectious, that has the additional feature of [[pulmonary consolidation]].<ref>{{cite book|title=Stedman's medical dictionary.|url=https://archive.org/details/stedmansmedicald00sted_3|url-access=registration|year=2006|publisher=Lippincott Williams & Wilkins|location=Philadelphia|isbn=978-0-7817-6450-6|edition=28th}}</ref> Pneumonia is most commonly classified by where or how it was acquired: community-acquired, aspiration, [[healthcare-associated pneumonia|healthcare-associated]], [[hospital-acquired pneumonia|hospital-acquired]], and ventilator-associated pneumonia.<ref name=Rad07>{{cite journal | vauthors = Sharma S, Maycher B, Eschun G | title = Radiological imaging in pneumonia: recent innovations | journal = Current Opinion in Pulmonary Medicine | volume = 13 | issue = 3 | pages = 159–69 | date = May 2007 | pmid = 17414122 | doi = 10.1097/MCP.0b013e3280f3bff4 | s2cid = 39554602 }}</ref> It may also be classified by the area of the lung affected: lobar, [[bronchial pneumonia]] and [[acute interstitial pneumonia]];<ref name=Rad07/> or by the causative organism.<ref>{{cite journal |vauthors=Dunn L |date=29 June – 5 July 2005 |title=Pneumonia: classification, diagnosis and nursing management |url=https://journals.rcni.com/doi/abs/10.7748/ns2005.06.19.42.50.c3901 |journal=Nursing Standard |volume=19 |issue=42 |pages=50–54 |doi=10.7748/ns2005.06.19.42.50.c3901 |pmid=16013205}}</ref> Pneumonia in children may additionally be classified based on signs and symptoms as non-severe, severe, or very severe.<ref>{{cite book |url=https://books.google.com/books?id=xbkbRG5XYxsC&pg=PA72 |title=Pocket Book of Hospital Care for Children: Guidelines for the Management of Common Illnesses with Limited Resources |publisher=World Health Organization |year=2005 |isbn=978-92-4-154670-6 |location=Geneva |page=72}}</ref>

The setting in which pneumonia develops is important to treatment,<ref name="Ana2009">{{cite journal |vauthors=Anand N, Kollef MH |date=February 2009 |title=The alphabet soup of pneumonia: CAP, HAP, HCAP, NHAP, and VAP |journal=Seminars in Respiratory and Critical Care Medicine |volume=30 |issue=1 |pages=3–9 |doi=10.1055/s-0028-1119803 |pmid=19199181|s2cid=260320494 }}</ref><ref name=ATS2005/> as it correlates to which pathogens are likely suspects,<ref name=Ana2009/> which mechanisms are likely, which antibiotics are likely to work or fail,<ref name=Ana2009/> and which complications can be expected based on the person's health status.

====Community====
{{Main|Community-acquired pneumonia}}
Community-acquired pneumonia (CAP) is acquired in the community,<ref name=Ana2009/><ref name=ATS2005/> outside of health care facilities. Compared with healthcare-associated pneumonia, it is less likely to involve [[multiple drug resistance|multidrug-resistant]] bacteria. Although the latter are no longer rare in CAP,<ref name=Ana2009/> they are still less likely. Prior stays in healthcare-related environments such as hospitals, nursing homes, or hemodialysis centers or a history of receiving domiciliary care can increase patients' risk for CAP caused by multidrug-resistant bacteria.<ref>{{cite journal |last1=Falcone |first1=Marco |last2=Russo |first2=Alessandro |last3=Giannella |first3=Maddalena |last4=Cangemi |first4=Roberto |last5=Scarpellini |first5=Maria Gabriella |last6=Bertazzoni |first6=Giuliano |last7=Alarcón |first7=José Martínez |last8=Taliani |first8=Gloria |last9=Palange |first9=Paolo |last10=Farcomeni |first10=Alessio |last11=Vestri |first11=Annarita |last12=Bouza |first12=Emilio |last13=Violi |first13=Francesco |last14=Venditti |first14=Mario |date=10 April 2015 |editor-last=Salluh |editor-first=Jorge IF |title=Individualizing Risk of Multidrug-Resistant Pathogens in Community-Onset Pneumonia |journal=PLOS ONE |language=en |volume=10 |issue=4 |pages=e0119528 |doi=10.1371/journal.pone.0119528 |issn=1932-6203 |pmc=4393134 |pmid=25860142|bibcode=2015PLoSO..1019528F |doi-access=free }}</ref> 

====Healthcare====
Health care–associated pneumonia (HCAP) is an infection associated with recent exposure to the health care system,<ref name=Ana2009/> including hospitals, outpatient clinics, [[nursing home]]s, [[Kidney dialysis|dialysis]] centers, [[chemotherapy]] treatment, or [[home care]].<ref name=ATS2005/> HCAP is sometimes called MCAP (medical care–associated pneumonia).

People may become infected with pneumonia in a hospital; this is defined as pneumonia not present at the time of admission (symptoms must start at least 48 hours after admission).<ref name="ATS2005">{{cite journal |author1=American Thoracic Society |author2=Infectious Diseases Society of America |date=February 2005 |title=Guidelines for the management of adults with hospital-acquired, ventilator-associated, and healthcare-associated pneumonia |url=https://www.atsjournals.org/doi/10.1164/rccm.200405-644ST |journal=American Journal of Respiratory and Critical Care Medicine |volume=171 |issue=4 |pages=388–416 |doi=10.1164/rccm.200405-644ST |pmid=15699079}}</ref><ref name=Ana2009/> It is likely to involve [[hospital-acquired infection]]s, with higher risk of [[multidrug-resistant]] pathogens. People in a hospital often have other medical conditions, which may make them more susceptible to pathogens in the hospital.

Ventilator-associated pneumonia occurs in people breathing with the help of mechanical ventilation.<ref name=Ana2009/><ref name=Ar2016/> Ventilator-associated pneumonia is specifically defined as pneumonia that arises more than 48 to 72 hours after [[endotracheal intubation]].<ref name=ATS2005/>

===Differential diagnosis===
Several diseases can present with similar signs and symptoms to pneumonia, such as: chronic obstructive pulmonary disease, asthma, [[pulmonary edema]], [[bronchiectasis]], lung cancer, and [[pulmonary emboli]].<ref name=BMJ06/> Unlike pneumonia, asthma and COPD typically present with wheezing, pulmonary edema presents with an abnormal [[electrocardiogram]], cancer and bronchiectasis present with a cough of longer duration, and pulmonary emboli present with acute onset sharp chest pain and shortness of breath.<ref name=BMJ06/> Mild pneumonia should be differentiated from upper respiratory tract infection (URTI). Severe pneumonia should be differentiated from [[acute heart failure]]. Pulmonary infiltrates that resolved after giving mechanical ventilation should point to heart failure and [[atelectasis]] rather than pneumonia. For recurrent pneumonia, underlying lung cancer, [[metastasis]], tuberculosis, a foreign bodies, immunosuppression, and hypersensitivity should be suspected.<ref name="Elena 2015">{{cite journal | vauthors = Prina E, Ranzani OT, Torres A | title = Community-acquired pneumonia | journal = Lancet | volume = 386 | issue = 9998 | pages = 1097–108 | date = September 2015 | pmid = 26277247 | pmc = 7173092 | doi = 10.1016/S0140-6736(15)60733-4 }}</ref>