Symptoms and Diagnosis
- Community-acquired pneumonia (CAP) presentation varies from mild pneumonia characterized by fever and productive cough to severe pneumonia characterized by respiratory distress and sepsis.1
- Diagnosis of pneumonia includes assessment of clinical features and a demonstrable infiltrate by chest radiograph or other imaging technique.2
- Even with extensive microbiological testing a causative pathogen is never identified in most patients with CAP.3
The clinical presentation of CAP varies, ranging from mild pneumonia characterized by fever and productive cough to severe pneumonia characterized by respiratory distress and sepsis.1 Most patients present with systemic evidence of infection, such as fever or chills and leukocytosis.4 Signs or symptoms localized to the respiratory system such as cough, increased sputum production, shortness of breath, or chest pain are also common.4
Key Elements of CAP4
For the diagnosis of pneumonia, in addition to clinical features, a demonstrable infiltrate by chest radiograph or other imaging technique, with or without supporting microbiological data, is required.2 Typical bacterial pneumonia infections are generally associated with a lobar pattern of opacity on a chest radiograph.5
Patient Chest Radiographs6
Chest X-rays of:
(A) A healthy person and
(B) A person with pneumonia.
All individuals are at risk for development of pneumonia. However, some individuals are more prone to pneumonia than are others due to the presence of certain comorbidities and lifestyle factors.7 Three-quarters of CAP patients aged 65–74 years have an underlying chronic condition, the most common are chronic cardiac disease, chronic pulmonary disease and diabetes.8,9
Once CAP is diagnosed, the severity must be evaluated as this impacts the treatment approach adopted. CAP guidelines from the American Thoracic Society (ATS)/ Infectious Diseases Society of America (IDSA) define severe CAP as present in patients with either one major criterion or three or more minor criteria.2
ATS/IDSA Criteria for Defining Severe CAP2
- Respiratory rate ≥30 breaths/min
- PaO2 /FiO2 ratio ≤250
- Multilobar infiltrates
- Uremia (blood urea nitrogen level ≥20 mg/dL)
- Leukopenia (white blood cell count <4,000 cells/µL)*
- Thrombocytopenia (platelet count <100,000/µL)
- Hypothermia (core temperature <36°C)
- Hypotension requiring aggressive fluid resuscitation
- Septic shock with need for vasopressors
- Respiratory failure requiring mechanical ventilation
Guidelines recommend the use of validated risk stratification tools, such as the pneumonia severity index (PSI; also known as the PORT score) or confusion, urea, respiratory rate, blood pressure, and 65 years of age or older (CURB-65) criteria to assist clinicians with site of care decision making (i.e., outpatient, hospitalization or admission to an intensive care unit).2,10,11 The PSI is preferred over CURB-65 and is composed of 20 items and classifies patients into five categories of severity that are associated with the risk of mortality. The risk category informs where and how the patient should be treated, and also provides general guidance for when microbiological testing should be requested.11
Current practice guidelines only recommend routine sputum and blood cultures in hospitalized patients with severe disease or risk factors for antibiotic resistant pathogens.2 However, even with extensive microbiological testing a causative pathogen is never identified in most patients with CAP.5
Sputum Gram stain and culture not recommended
Recommended in patients with severe disease as well as in all inpatients empirically treated for MRSA or P. aeruginosa
Legionella and Pneumococcal Urinary Antigen
Recommended in adults with severe CAP or associated with a Legionella outbreak
Rapid influenza molecular assay, when influenza is circulating in the community
- Ramirez JA. Overview of community-acquired pneumonia in adults. Available from: https://www.uptodate.com/contents/overview-of-communityacquired-pneumonia-in-adults/print (accessed February 15 2021).
- Metlay JP, Waterer GW, Long AC, et al. 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. Am J Respir Crit Care Med. 2019;200(7):e45-e67.
- Musher DM, Abers MS, Bartlett JG. Evolving understanding of the causes of pneumonia in adults, with special attention to the role of Pneumococcus. Clin Infect Dis. 2017;65(10):1736-1744.
- Wunderink RG, Waterer GW. Clinical practice. Community-acquired pneumonia. N Engl J Med. 2014;370(6):543-551.
- Musher DM, Thorner AR. Community-acquired pneumonia. N Engl J Med. 2014;371(17):1619-1628.
- Hashmi MF, Katiyar S, Keskar AG, et al. Efficient Pneumonia Detection in Chest X-ray Images Using Deep Transfer Learning. Diagnostics. 2020; 10(6):417.
- Prina E, Ranzani OT, Torres A. Community-acquired pneumonia. Lancet. 2015;386(9998):1097-1108.
- Ramirez JA, Wiemken TL, Peyrani P, et al. Adults hospitalized with pneumonia in the United States: Incidence, epidemiology, and mortality. Clin Infect Dis. 2017;65(11):1806-1812.
- Fry AM, Shay DK, Holman RC, et al. Trends in hospitalizations for pneumonia among persons aged 65 years or older in the United States, 1988-2002. JAMA. 2005;294(21):2712-2719.
- Lim WS, van der Eerden MM, Laing R, et al. Defining community acquired pneumonia severity on presentation to hospital: an international derivation and validation study. Thorax. 2003;58(5):377-382.
- Fine MJ, Auble TE, Yearly DM, et al. A prediction rule to identify low-risk patients with community-acquired pneumonia. N Engl J Med. 1997;336(4):243-250.