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Community-acquired pneumonia

Definition
CAP is an acute infection of the lungs occurring in an individual who has had little contact with the healthcare system.
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Pathophysiology
Common causes of CAP include bacterial infections (such as S. pneumoniae, H. influenzae, S. aureus) and respiratory viruses (such as influenza virus, RSV, adenovirus, coronavirus, human metapneumovirus, rhinovirus). No causative organism is identified in over 50% of patients.
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Epidemiology
In the US, the incidence of CAP is estimated at 248 cases per 100,000 person-years. In adults ≥ 65 years of age, the incidence increases to 630-1640 cases per 100,000 person-years.
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Disease course
The most common complications of CAP include respiratory failure, metastatic infections, complicated pleural effusion, sepsis, and multiorgan failure. Influenza and bacterial pneumonia are strongly associated with cardiac events including myocardial infarction, arrhythmias, and HF.
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Prognosis and risk of recurrence
In patients requiring hospitalization, CAP is associated with an estimated in-hospital mortality of 11%.
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Key sources
The following summarized guidelines for the evaluation and management of community-acquired pneumonia are prepared by our editorial team based on guidelines from the Society of Critical Care Medicine (SCCM 2024; 2015), the American Academy of Family Physicians (AAFP 2023; 2022; 2021; 2020; 2017; 2015; 2012), the European Society of Intensive Care Medicine (ESICM/ALAT/ERS/ESCMID 2023), the British Thoracic Society (BTS 2023; 2011), the European Federation of Societies for Ultrasound in Medicine and Biology (EFSUMB 2022), the Center for Disease Control (CDC 2022; 2019), the American College of Emergency Physicians (ACEP 2021), the American Thoracic Society (ATS 2021; 2019), the American College of Physicians (ACP 2021), the Infectious Diseases Society of America (IDSA/ATS 2019), the American College of Chest Physicians (ACCP 2019), the Infectious Diseases Society of America (IDSA/PIDS 2011), and the Infectious Diseases Society of America (IDSA 2007).
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Guidelines

1.Screening and diagnosis

Diagnostic criteria: diagnose pneumonia on the basis of a demonstrable infiltrate by CXR or other imaging technique, with or without supporting microbiological data, in addition to a constellation of suggestive clinical features.
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2.Classification and risk stratification

Risk prediction rules: as per ACEP 2021 guidelines, consider using the PSI and CURB-65 decision aids to support clinical judgment to identify patients at low risk of mortality appropriate for outpatient treatment.
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3.Diagnostic investigations

History and physical examination: consider assessing for clinical symptoms and signs suggestive of pneumonia (cough, dyspnea, pleural pain, sweating, shivers, pains, fever ≥ 38 °C, tachypnea, new and localizing chest examination signs) in adult outpatients with acute cough due to suspected pneumonia.
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  • Travel history

  • CXR

  • Chest ultrasound

  • CRP

  • Procalcitonin

  • Indications for microbiological testing

  • Sputum cultures (outpatient setting)

  • Sputum cultures (inpatient setting)

  • Sputum cultures (Legionella)

  • Sputum cultures (fungal/tuberculosis)

  • Sputum PCR

  • Urinary antigens (pneumococcal, non-severe CAP)

  • Urinary antigens (pneumococcal, severe CAP)

  • Urinary antigens (Legionella, non-severe CAP)

  • Urinary antigens (Legionella, severe CAP)

  • Blood cultures (outpatient setting)

  • Blood cultures (inpatient setting, nonsevere CAP)

  • Blood cultures (inpatient setting, severe CAP)

  • Viral testing (influenza)

  • Viral testing (non-influenza)

  • Fungal testing (invasive aspergillosis)

  • Fungal testing (invasive candidiasis)

  • Fungal testing (coccidioidomycosis)

  • Fungal testing (histoplasmosis)

  • Fungal testing (blastomycosis)

  • Screening for occult adrenal insufficiency

4.Respiratory support

High-flow nasal oxygen therapy: consider initiating high-flow nasal oxygen therapy instead of standard oxygen supplementation in patients with severe CAP and acute hypoxemic respiratory failure not requiring immediate intubation.
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  • Noninvasive ventilation

5.Medical management

Setting of care, hospital admission: offer more intensive treatment (hospitalization or intensive in-home health care services where appropriate and available) in patients with CURB-65 scores ≥ 2.
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  • Setting of care (ICU admission)

  • Empiric antibiotic therapy (outpatient setting, initiation)

  • Empiric antibiotic therapy (outpatient setting, patients without comorbidities)

  • Empiric antibiotic therapy (outpatient setting, patients with comorbidities)

  • Empiric antibiotic therapy (emergency department)

  • Empiric antibiotic therapy (inpatient setting, nonsevere CAP)

  • Empiric antibiotic therapy (inpatient setting, severe CAP)

  • Definitive antibiotic therapy

  • Duration of antibiotic therapy

  • Corticosteroids

  • Anti-influenza therapy

6.Nonpharmacologic interventions

Smoking cessation: advise smoking cessation in smoker patients hospitalized with CAP.
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7.Specific circumstances

Pediatric patients, immunizations, AAFP: offer childhood and maternal immunizations against bacterial and viral pathogens to decrease the risk of pneumonia.
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  • Pediatric patients (RSV monoclonal antibodies)

  • Pediatric patients (clinical assessment)

  • Pediatric patients (chest imaging)

  • Pediatric patients (routine laboratory tests)

  • Pediatric patients (microbiological testing, general principles)

  • Pediatric patients (microbiological testing, blood culture)

  • Pediatric patients (microbiological testing, testing for atypical bacteria)

  • Pediatric patients (microbiological testing, urinary testing)

  • Pediatric patients (microbiological testing, viral testing)

  • Pediatric patients (microbiological testing, upper respiratory tract specimens)

  • Pediatric patients (microbiological testing, lower respiratory tract specimens)

  • Pediatric patients (microbiological testing, pleural fluid specimens)

  • Pediatric patients (setting of care, outpatient)

  • Pediatric patients (setting of care, intpatient)

  • Pediatric patients (setting of care, ICU)

  • Pediatric patients (antibiotic therapy, general principles)

  • Pediatric patients (antibiotic therapy, outpatient regimens)

  • Pediatric patients (antibiotic therapy, inpatient regimens)

  • Pediatric patients (antibiotic therapy, duration)

  • Pediatric patients (antibiotic therapy, prevention of resistance)

  • Pediatric patients (antiviral therapy)

  • Pediatric patients (supplemental oxygen)

  • Pediatric patients (nasogastric tube)

  • Pediatric patients (chest physiotherapy)

  • Pediatric patients (management of parapneumonic effusion)

  • Pediatric patients (management of pulmonary abscess)

  • Pediatric patients (repeat imaging)

  • Pediatric patients (repeat laboratory testing)

  • Pediatric patients (re-evaluation)

  • Pediatric patients (management of refractory disease)

  • Pediatric patients (discharge from hospital)

  • Pediatric patients (post-discharge follow-up)

  • Nursing home residents

  • Patients with aspiration pneumonia (diagnosis)

  • Patients with aspiration pneumonia (maintenance of oral health)

  • Patients with aspiration pneumonia (management of swallowing difficulties)

  • Patients with aspiration pneumonia (choice of antibiotics)

  • Patients with aspiration pneumonia (thromboprophylaxis)

  • Patients with aspiration pneumonia (supportive and palliative care)

8.Preventative measures

Pneumococcal vaccination: as per AAFP 2022 guidelines, offer PCV20 alone or PCV15 followed by PPSV23 1 year later for the prevention of pneumonia in all adults aged ≥ 65 years or 19-64 years having comorbid or immunocompromising conditions.
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9.Follow-up and surveillance

Hospital discharge criteria: discharge patients as soon as they are clinically stable, have no other active medical problems, and have a safe environment for continued care. Avoid offering inpatient observation while administering oral therapy.
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  • Serial imaging assessment