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Community-acquired pneumonia (CAP) is an acute infection of the pulmonary parenchyma acquired outside a hospital or healthcare setting, usually due to bacteria, viruses, or atypical organisms. It is the most common form of pneumonia encountered clinically.

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Etiology


Organism Type Common Pathogens
Typical bacteria Streptococcus pneumoniae (most common), Haemophilus influenzae, Moraxella
Atypical bacteria Mycoplasma pneumoniae, Chlamydophila pneumoniae, Legionella pneumophila
Viral Influenza A/B, SARS-CoV-2, RSV, adenovirus
Others Klebsiella, Staphylococcus aureus (esp. post-influenza), aspiration flora

![Prevalence of microbial aetiologies of CAP in the USA and Europe: a | Aetiology of community-acquired pneumonia (CAP) in the adult population in the USA from 2010 to 2012 (from 2,488 cases) b | Aetiology of CAP in the adult population in Europe from 2003 to 2014 (from 3,854 cases) Possible reasons that may explain the challenge in identifying the aetiology of pneumonia include difficulty in obtaining samples from the lower respiratory tract, the effect of antibiotic use prior to sample collection and low sensitivity of some diagnostic tests.

Torres, A., Cilloniz, C., Niederman, M.S. et al. Pneumonia. Nat Rev Dis Primers 7, 25 (2021). https://doi.org/10.1038/s41572-021-00259-0](attachment:be0a9934-f60e-4d48-88e1-8f12decf7e89:41572_2021_259_Fig1_HTML.webp)

Prevalence of microbial aetiologies of CAP in the USA and Europe: a | Aetiology of community-acquired pneumonia (CAP) in the adult population in the USA from 2010 to 2012 (from 2,488 cases) b | Aetiology of CAP in the adult population in Europe from 2003 to 2014 (from 3,854 cases) Possible reasons that may explain the challenge in identifying the aetiology of pneumonia include difficulty in obtaining samples from the lower respiratory tract, the effect of antibiotic use prior to sample collection and low sensitivity of some diagnostic tests.

Torres, A., Cilloniz, C., Niederman, M.S. et al. Pneumonia. Nat Rev Dis Primers 7, 25 (2021). https://doi.org/10.1038/s41572-021-00259-0

![Prevalence of microbial aetiologies of CAP in India and China: a | Aetiology of community-acquired pneumonia (CAP) in the adult population in India from 2013 to 2015 (from 225 cases).  b | Aetiology of CAP in the adult population in China from 2004 to 2005 (from 593 cases). Possible reasons that may explain the challenge in identifying the aetiology of pneumonia include difficulty in obtaining samples from the lower respiratory tract, the effect of antibiotic use prior to sample collection and low sensitivity of some diagnostic tests. MRSA, methicillin-resistant Staphylococcus aureus; MSSA, methicillin-susceptible Staphylococcus aureus.

Torres, A., Cilloniz, C., Niederman, M.S. et al. Pneumonia. Nat Rev Dis Primers 7, 25 (2021). https://doi.org/10.1038/s41572-021-00259-0](attachment:f814f275-c3da-4624-82dd-79ff606c363c:41572_2021_259_Fig2_HTML.webp)

Prevalence of microbial aetiologies of CAP in India and China: a | Aetiology of community-acquired pneumonia (CAP) in the adult population in India from 2013 to 2015 (from 225 cases).  b | Aetiology of CAP in the adult population in China from 2004 to 2005 (from 593 cases). Possible reasons that may explain the challenge in identifying the aetiology of pneumonia include difficulty in obtaining samples from the lower respiratory tract, the effect of antibiotic use prior to sample collection and low sensitivity of some diagnostic tests. MRSA, methicillin-resistant Staphylococcus aureus; MSSA, methicillin-susceptible Staphylococcus aureus.

Torres, A., Cilloniz, C., Niederman, M.S. et al. Pneumonia. Nat Rev Dis Primers 7, 25 (2021). https://doi.org/10.1038/s41572-021-00259-0

Clinical Features


Symptom Characteristic
Fever and chills Often abrupt in onset
Cough May be productive or dry
Dyspnea Mild to severe, depending on extent
Chest pain Often pleuritic
Auscultation findings Rales, bronchial breath sounds, egophony
Elderly/atypical hosts May show confusion or subtle signs

CURB-65: Prognostic Scoring

Score 1 each: