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{{AdultPage|pneumonia (peds)}}
==Background==
[[File:Lung and diaphragm.jpg|thumb|Lobes of the lung with related anatomy.]]
*Definition: infection of lung parenchyma
*Most common infectious cause of death in the United States; >1.5 million adults hospitalized annually for CAP<ref name="Jain2015">Jain S, Self WH, Wunderink RG, et al. Community-Acquired Pneumonia Requiring Hospitalization among U.S. Adults. N Engl J Med. 2015;373(5):415-427.</ref>
*Up to 50% of cases have no pathogen identified even with extensive workup<ref name="Jain2015"/>
*Empirically classified based upon location/risk factors

===Pneumonia Empiric Categories===
''The term "health care-associated pneumonia" (HCAP) is no longer used.<ref name="ATS2019"> 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 [https://www.atsjournals.org/doi/full/10.1164/rccm.201908-1581ST Am J Respir Crit Care Med. 2019 Oct 1;200(7):e45-e67] </ref> It previously referred to pneumonia acquired in any healthcare facility (e.g., nursing home, hemodialysis center, recent hospitalization) and was used to identify patients at risk for infection with multidrug-resistant pathogens. However, this inappropriately led to increased inappropriately broad antibiotic use and was thus retired. Patients previously classified as HCAP should in general be treated as CAP with exceptions as below under resistant pathogens.''
*Community-acquired pneumonia (CAP): Acquired outside of the hospital
*Nosocomial pneumonia: Acquired in a hospital setting
**Hospital-acquired pneumonia (HAP): Acquired ≥48 hours after hospital admission
**Ventilator-associated pneumonia (VAP): Acquired ≥48 hours after [[endotracheal intubation]]

===Resistant Pathogen Risk Factors===
''IDSA recommends covering empirically for resistant pathogens (e.g., [[MRSA]], [[pseudomonas]]) in adults with CAP only if there is a treatment regimen based on "locally validated" risk factors. In that case, may give empiric coverage while awaiting culture results.''<ref name="ATS2019"/>
*Commonly accepted risk factors historically include:
**Prior respiratory isolation of MRSA or ''P. aeruginosa''
**Recent hospitalization AND receipt of parenteral antibiotics (in the last 90 days)
**Nursing home/long-term care residents
**[[Dialysis complications|Dialysis]]
**Receiving chronic wound care
**Receiving chemotherapy
**Immunosuppression (including steroids)
**[[Alcoholism]]
**Structural lung disease
**[[Malnutrition]]

===Commonly Encountered Pathogens by Risk Factor===
{| {{table}}
| align="center" style="background:#f0f0f0;"|'''Risk Factor'''
| align="center" style="background:#f0f0f0;"|'''Associated Organism'''
|-
| [[Alcoholism]]||
*[[Streptococcus pneumoniae]]
*[[Anaerobes]] (e.g. [[Klebsiella pneumoniae]]) 
*[[Mycobacterium tuberculosis]]
|-
| *Aspiration||
*[[Anaerobes]]
|-
| [[COPD]] and/or Smoking||
*[[S. pneumoniae ]]
*[[Haemophilus influenzae]] 
*[[Moraxella ]]
*[[Legionella]]
|-
| Nursing Home||
*[[S. pneumoniae ]]
*[[Gram-negative]] bacilli 
*[[H. influenzae ]]
*[[Staphylococcus aureus ]]
*[[Anaerobes]] 
*[[Chlamydophila pneumoniae]]
|-
| Exposure to bird droppings||
*[[Histoplasma capsulatum]]
|-
| Exposure to birds||
*[[Chlamydophila psittaci]]
|-
| Exposure to rabbits||
*[[Francisella tularensis]]
|-
| Exposure to farm animals||
*[[Coxiella burnetii]] (Q fever)
|-
| Exposure to southwestern US||
*[[Coccidiomycosis]] (Valley fever)
|-
| Early [[HIV]]||
*[[S. pneumoniae ]]
*[[H. influenzae ]]
*[[M. tuberculosis]]
|-
| Late [[HIV]] (as above, plus:)||
*[[Pneumocystis jiroveci]] 
*[[Cryptococcus ]]
*[[Histoplasma]]
|-
| Structural Lung Disease ([[Cystic fibrosis|CF]], [[bronchiectasis]])||
*[[Pseudomonas aeruginosa ]]
*[[Burkholderia cepacia ]]
*[[S. aureus]]
|-
| [[Injection drug use]]||
*[[S. aureus ]]
*[[Anaerobes ]]
*[[M. tuberculosis ]]
*[[S. Pneumo]]
|-
| [[Influenza]]||
*Influenza 
*[[S. pneumoniae ]]
*[[S. aureus ]]
*[[H. influenzae]]
|-
| Ventilator Associated Pneumonia||
*[[Pseudomonas aeruginosa ]]
*[[Acinetobacter]] sp. 
*[[Stenotrophomonas maltophilia]]
|}

{{Causes of pneumonia}}

==Clinical Features==
*[[Fever]], chills, pleuritic [[chest pain]], productive [[cough]]
**Fever is seen in 80%
*[[Tachypnea]]
**Most sensitive sign in elderly 
*[[Abdominal pain]], [[nausea and vomiting]], [[diarrhea]] may be seen with [[Legionella]] infection
*[[Myalgia]], [[fatigue]]

===ED Pearls===
*'''Elderly/immunocompromised patients''' may present atypically: [[altered mental status]], [[falls]], functional decline, or [[hypothermia]] rather than classic fever and cough<ref name="Feldman1999">Feldman C. Pneumonia in the elderly. Clin Chest Med. 1999;20(3):563-573. doi:10.1016/s0272-5231(05)70236-7</ref>
*Tachypnea (RR >24) is the most sensitive vital sign finding in elderly patients and should prompt evaluation even in the absence of typical symptoms
*[[Sepsis (Main)|Sepsis]] screening should be performed in all patients with suspected pneumonia; pneumonia is the most common cause of [[sepsis]]
*Patients with lower lobe pneumonia may present with predominantly upper [[abdominal pain]], mimicking an acute abdomen

==Differential Diagnosis==
{{SOB DDX}}

==Evaluation==
[[File:PneumonisWedge09.jpg|thumb|[[CXR]] showing prominent wedge-shape area of airspace consolidation in the right lung, characteristic of bacterial [[pneumonia]].]]
[[File:RLLpneumonia.png|thumb|Right lower lobe pneumonia as seen on lateral CXR.]]
[[File:XR chest - pneumonia with abscess and caverns - d0.jpg |thumb|[[CXR]] showing pneumonia with [[lung abscess]].]]
[[File:CT scan of the chest, demonstrating right-sided pneumonia.jpg|thumb|CT chest showing right sided pneumonia]]
[[File:PNA_US.gif|thumb|Hepatization of the lung and dynamic air bronchograms present in patient with LLL pneumonia. Source: POCUS Atlas]]
===Workup===
*[[CXR]]
**May have negative CXR early in disease or in cases of dehydration; infiltrate may "blossom" after providing rehydration and repeat imaging<ref name="Feldman1999"/>
**Absence of CXR findings does not preclude diagnosis; high clinical suspicion with adventitious breath sounds can be consistent with pneumonia despite negative imaging
**Immunocompromised patients may not manifest radiographic evidence of pneumonia despite suggestive clinical findings
**Clinical and radiographic findings do not necessarily correspond: the patient may be improving clinically despite having a worsening appearance on the CXR
*[[Ultrasound]]
**Can be considered as an alternative to CXR
**Sensitivity 82% and specificity 94%<ref name="Staub2019">Staub LJ, Mazzali Biscaro RR, Kaszubowski E, Maurici R. Lung Ultrasound for the Emergency Diagnosis of Pneumonia, Acute Heart Failure, and Exacerbations of Chronic Obstructive Pulmonary Disease/Asthma in Adults: A Systematic Review and Meta-analysis. J Emerg Med. 2019;56(1):53-69. doi:10.1016/j.jemermed.2018.09.009</ref>
**Key findings: hepatization of lung tissue, dynamic air bronchograms, B-lines, and subpleural consolidation
**Particularly useful for identifying parapneumonic [[pleural effusion]]
*CBC 
*Chemistry (including BUN, glucose for PSI scoring)
*[[Lactate]] if concern for [[sepsis]]
*IDSA does not support using initial serum [[procalcitonin]] levels to determine whether empiric antibiotics should be initiated<ref name="ATS2019"/>
**Clinical judgement ''plus'' radiographic evidence alone should guide therapy (strong recommendation, moderate quality of evidence)
**Procalcitonin sensitivity for detecting bacterial infection ranges from 38% to 91%; not accurate enough to justify withholding antibiotics<ref name="AAFP2020">Metlay JP, Waterer GW. Update on Community-Acquired Pneumonia: Updated Recommendations from the ATS and IDSA. Am Fam Physician. 2020;102(2):120-121.</ref>

If patient will be admitted: 

*[[Blood Cultures]] are ONLY indicated for CAP patients with:<ref name="ATS2019"/>
**ICU admission (required)
**Empiric treatment for [[MRSA]] or ''[[Pseudomonas aeruginosa|P. aeruginosa]]'' (required)
**Prior MRSA or ''P. aeruginosa'' respiratory infection
**Recent hospitalization AND parenteral antibiotics in the last 90 days
**Multi-lobar infiltrates
**Pleural effusion
**Cavitary lesions 
**Leukopenia
**The yield of blood cultures is low (2% to 9%) in adults without severe CAP, and empiric therapy is rarely changed based on these results<ref name="AAFP2020"/>
*Sputum Gram stain and culture: recommended for the same indications as blood cultures above<ref name="ATS2019"/>
**Lower respiratory tract samples from intubated patients should be sent for Gram stain and culture shortly after intubation (higher yield than sputum)
*MRSA nasal PCR (if available): High negative predictive value (~95%) for ruling out MRSA pneumonia; useful for de-escalation of empiric MRSA coverage<ref name="Parente2018">Parente DM, Cunha CB, Engemann AM, et al. The Clinical Utility of Methicillin-Resistant Staphylococcus aureus (MRSA) Nasal Screening to Rule Out MRSA Pneumonia: A Diagnostic Meta-analysis With Antimicrobial Stewardship Implications. Clin Infect Dis. 2018;67(1):1-7.</ref>
*Legionella and Pneumococcal urinary antigen testing: Not routinely recommended; consider for:<ref name="ATS2019"/>
**Severe CAP (ICU patients)
**Legionella antigen in alcoholics, outbreaks, or recent (within 2 weeks) travel history
*Influenza testing: Recommended when influenza is circulating in the community; molecular testing (PCR) preferred over rapid antigen<ref name="ATS2019"/>

===Chest X-Ray Mimics===
*Malignancy
*Tuberculosis
*[[Pulmonary embolism]] - Hampton's hump
*[[Pleural effusion]]
*Atelectasis
*[[ARDS]]
*[[Diffuse alveolar hemorrhage]]
*Multiple "cannonball" infiltrates
**Metastatic disease
**Septic emboli
**Right sided [[endocarditis]]

===IDSA Severe Pneumonia Criteria===
Severe pneumonia can be diagnosed with either one major criterion or three or more minor criteria.<ref name="Severity">Severe pneumonia can be diagnosed with either one major criterion or three or more minor criteria.  Neth J Med. 1999 Sep;55(3):110-7 10.1016/s0300-2977(99)00071-6</ref> These criteria have a pooled sensitivity of 84% and specificity of 78% for predicting ICU admission.<ref name="ATS2019"/>
====Minor criteria====
*Respiratory rate > 30 breaths/min
*PaO2/FiO2 ratio < 250
*Multi-lobar infiltrates
*Confusion/disorientation
*Uremia (blood urea nitrogen level > 20 mg/dl)
*Leukopenia (WBC < 4,000 cells/µL)
*[[Thrombocytopenia]] (platelet count < 100,000 cells/µL)
*[[Hypothermia]] (<36°C)
*[[Hypotension]] requiring aggressive fluid resuscitation
====Major criteria====
*Septic shock with need for vasopressors
*Respiratory failure requiring mechanical ventilation

==Management==
{{Pneumonia Antibiotics}}

===Adjunctive Corticosteroids===
''Updated guidance based on CAPE COD trial (2023) and SCCM 2024 Focused Update:''

*The SCCM 2024 Focused Update strongly recommends corticosteroids for adult patients hospitalized with severe bacterial CAP (strong recommendation, moderate certainty of evidence)<ref name="SCCM2024">Chaudhuri D, Nei AM, Rochwerg B, et al. 2024 Focused Update: Guidelines on Use of Corticosteroids in Sepsis, Acute Respiratory Distress Syndrome, and Community-Acquired Pneumonia. Crit Care Med. 2024;52(5):e219-e233.</ref>
**No recommendation for or against steroids in less severe CAP
*The CAPE COD trial (NEJM 2023): IV hydrocortisone 200 mg/day in severe CAP requiring ICU/intermediate care admission showed:<ref name="CAPECOD">Dequin PF, Meziani F, Quenot JP, et al. Hydrocortisone in Severe Community-Acquired Pneumonia. N Engl J Med. 2023;388(21):1931-1941.</ref>
**↓ 28-day mortality (6.2% vs 11.9%; absolute difference 5.6%; NNT ~18)
**↓ Need for intubation
**↓ Need for vasopressors
**Duration: hydrocortisone 200 mg/day for 4 or 7 days based on clinical improvement, then tapered (total 8 or 14 days)
**Excluded patients already in [[sepsis|septic shock]]
*REMAP-CAP (2025): Fixed-dose hydrocortisone 200 mg/day x 7 days in severe CAP triggered a futility stopping rule for 90-day mortality; however, this trial enrolled a more severely ill population with higher rates of septic shock than CAPE COD<ref name="REMAPCAP">REMAP-CAP Investigators. Effect of hydrocortisone on mortality in patients with severe community-acquired pneumonia. Intensive Care Med. 2025.</ref>
*Practical approach for the ED:
**If patient has severe CAP (meets IDSA/ATS severity criteria, hypoxic, or being admitted to the ICU), consider hydrocortisone 200 mg IV daily (50 mg q6h) or methylprednisolone 40 mg IV daily
**No clear benefit in non-severe CAP
**Avoid in active influenza pneumonia (without bacterial superinfection) per 2019 ATS/IDSA<ref name="ATS2019"/>

===Aspiration Pneumonia===
''See also: [[Aspiration pneumonia and pneumonitis]]''
*2019 ATS/IDSA guidelines recommend against routinely adding anaerobic coverage beyond standard CAP empiric antibiotics in suspected aspiration pneumonia (conditional recommendation, very low quality of evidence)<ref name="ATS2019"/>
**Exception: Add anaerobic coverage (e.g. [[ampicillin-sulbactam]], [[clindamycin]], or carbapenem) if [[lung abscess]] or [[empyema]] is suspected
*Rationale: More recent studies show anaerobes are uncommon causes of aspiration pneumonia; unnecessary anaerobic coverage increases risk of ''[[Clostridioides difficile]]'' infection without mortality benefit<ref name="Tessier2024">Tessier L, Bhatt M, Engert JC, et al. Anaerobic Antibiotic Coverage in Aspiration Pneumonia and the Associated Benefits and Harms: A Retrospective Cohort Study. Chest. 2024;166(3):488-497.</ref>
*Aspiration pneumonitis (chemical/inflammatory reaction without infection): supportive care only; antibiotics are not indicated unless infection develops

===Influenza-Associated Pneumonia===
*'''Anti-influenza treatment''' (e.g. [[oseltamivir]]) should be prescribed to all adults with CAP who test positive for influenza, regardless of duration of illness or hospitalization status<ref name="ATS2019"/>
*Standard antibacterial treatment should also be initially prescribed alongside antivirals in patients with clinical and radiographic evidence of CAP who test positive for influenza<ref name="ATS2019"/>
*Avoid routine corticosteroids in influenza pneumonia<ref name="ATS2019"/>

===Treatment Duration and De-escalation===
*Minimum 5 days of antibiotics<ref name="ATS2019"/>
*Continue until the patient achieves clinical stability, defined as:
**Temperature ≤37.8°C
**Heart rate ≤100 bpm
**Respiratory rate ≤24
**Systolic BP ≥90 mmHg
**SpO2 ≥90% on room air
**Able to take oral intake
**Normal mental status (back to baseline)
*De-escalation: If empiric MRSA or ''Pseudomonas'' coverage was started, de-escalate to standard CAP therapy within 48 hours if cultures and MRSA nasal PCR are negative and the patient is improving<ref name="ATS2019"/>

===Treatment Failure===
''Consider the following if patient is not improving at 48-72 hours:''
*Incorrect diagnosis (see [[#Chest X-Ray Mimics|CXR Mimics]] above)
*Resistant or unusual organism (obtain cultures if not already done)
*Complications: [[empyema]], [[lung abscess]], parapneumonic effusion
*Inadequate antibiotic dosing or penetration
*Superinfection (e.g. ''C. difficile'')
*Immunocompromised state not initially recognized
*Noninfectious mimic (e.g. [[pulmonary embolism]], malignancy)
*Consider CT chest for complications not visible on CXR

==Disposition==
*Use clinical judgment plus [[PORT Score]] (PSI) to guide disposition per IDSA 2019 guidelines<ref name="ATS2019"/>
*Discharge (PSI class I-II):
**Able to tolerate oral medications
**No hypoxia, hemodynamic instability, or significant comorbidities
**Reliable follow-up in 48-72 hours
*Admit to floor (PSI class III-IV):
**Hypoxia requiring supplemental O2
**Inability to tolerate oral medications
**Significant comorbidity (immunocompromised, decompensated CHF, etc.)
*Admit to ICU (PSI class V, or meeting major/minor criteria):
**Requiring vasopressors or mechanical ventilation (major criteria)
**3 or more minor criteria: RR >30, PaO2/FiO2 <250, multilobar infiltrates, confusion, BUN >20, WBC <4, platelets <100, hypothermia, hypotension requiring aggressive fluids


==Prognosis==
*Half of patients are still symptomatic at 30 days, with a significant minority experiencing chest pain, malaise or mild dyspnea even 2 to 3 months after treatment
*In adults with CAP whose symptoms have resolved within 5-7 days, it is not recommended to routinely obtain follow-up chest imaging<ref name="ATS2019"/>
*Consider follow-up imaging in 7-12 weeks for patients at higher risk for malignancy (e.g. smokers >50 years) to ensure resolution and exclude underlying malignancy

==See Also==
*[[Pneumonia (Pathogens)]]
*[[Pneumonia (Peds)]]
*[[Ventilator associated pneumonia]]
*[[Aspiration pneumonia and pneumonitis]]
*[[Antibiotics by diagnosis]]
*[[CURB-65]]
*[[Sepsis (Main)]]

== Calculators ==
{{PSI Calculator}}
{{PORT Score Calculator}}
{{CURB65_Calculator}}

{{PSI_PORT_Calculator}}

==External Links==
*[http://www.mdcalc.com/curb-65-severity-score-community-acquired-pneumonia/ MDCalc - CURB-65 Severity Score]
*[http://www.mdcalc.com/psi-port-score-pneumonia-severity-index-adult-cap/ MDCalc - PSI/PORT Score]
*[https://www.atsjournals.org/doi/full/10.1164/rccm.201908-1581ST ATS/IDSA 2019 CAP Guidelines (Full Text)]
*[http://cid.oxfordjournals.org/content/early/2016/07/06/cid.ciw353.full.pdf IDSA/ATS 2016 HAP/VAP Guidelines (Full Text)]

==References==
{{reflist|2}}
[[Category:ID]]
[[Category:Pulmonary]]