Pneumonia, Community-Acquired

Communal
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Diagnosis and reasoning

This elderly gentleman has presented with signs and symptoms suggestive of a left-sided pneumonia; given the lack of previous contact with the health care system, this is most likely a community acquired pneumonia (CAP). A complete blood count (CBC) and posteroanterior chest x-ray are good initial confirmatory tests; in the former, the presence of a neutrophil leukocytosis favors a bacterial infection. Note that an unremarkable chest x-ray does not exclude a pneumonia, as radiographs can be normal in early disease; more importantly, there are no features suggestive of complications such as synpneumonic effusions or multilobar disease. Risk stratification is key to the further management of this patient; this is most simply achieved via the CURB-65 score. Note that this requires a blood urea nitrogen (BUN) level. This patient's BUN level turns out to be 14 mg/dL; thus, his CURB-65 score is 0, i.e. he is at low risk for mortality, and can be treated at home. Thus, he should be started on empirical antibiotic therapy (for example, a fluoroquinolone such as Ciprofloxacin); Acetaminophen should be prescribed as an antipyretic. Note that sputum cultures are not recommended in low-risk patients with CAP, especially if the symptoms are of short duration. This is because positive culture rates are low in such patients. Furthermore, conventional chest physiotherapy has not been shown to improve the morbidity or mortality of CAP.


Discussion

Community acquired pneumonia (CAP) is defined as pneumonia acquired outside a hospital or long-term care facility; in the United States, an estimated 5.6 million cases occur annually, with an associated health care cost of $8.4 billion. With such patients, the key decision is whether they should be managed at home, or in a hospital. Note that unnecessary hospitalization is expensive, running to an average expense of $7,500 per patient, while also exposing these individuals to nosocomial pathogens. That said, while outpatient care is of negligible cost, treatment of high-risk patients at home results in increased morbidity and mortality. The decision between inpatient and outpatient treatment can be aided by the judicious use of prospectively validated clinical prediction tools to conduct an objective risk assessment. The most notable of these tools are the Pneumonia Severity Index (PSI) and the CURB-65 score. The PSI is a clinical prediction rule which utilizes 20 different variables; these include demographics, symptomatology, medical history, comorbidities, physical examination findings and investigation results. Patients are stratified into 5 risk categories, which predict 30 day survival; those in risk classes I, II, or III can be treated in a primary care setting. Unfortunately, while sensitive and specific, the PSI score is tedious to perform, and requires multiple invasive investigations; in most primary care settings, the less sensitive, but much simpler CURB-65 score is a better tool. This only involves 5 variables (presence of confusion, blood urea nitrogen, respiratory rate, blood pressure, and age equal or more than 65 years); if blood testing is unavailable, a 4 variable substitute (CRB-65) can be used instead. Note that while the British Thoracic Society (BTS) specifically recommends the use of either CURB-65 or CRB-65, the American Thoracic Society (ATS) only recommends the use of a validated risk assessment tool, leaving the exact tool upto the discretion of the treating clinician. Another key point to appreciate is that the above tools are not a substitute for good clinical judgement, and should not be applied mindlessly. Antibiotic therapy is the cornerstone of CAP management; empirical antibiotic therapy covering both the common 'typical' pathogens (S. pneumoniae, H. influenzae and M. catarrhalis) and the common atypical agents (mycoplasma, chlamydophila, and legionella) should be initiated without delay. The ATS and Infectious disease society of America (IDSA) recommend monotherapy with a macrolide, a fluoroquinolone, or doxycycline initially; in patients who show a poor response to the above, a beta lactam such as ceftriaxone can be added. However, several studies have shown that approximately 25% of S. pneumoniae strains are now resistant to all macrolides; furthermore, a recent guideline by the therapeutic working group of the Centers for Disease Control and Prevention (CDC) recommends that fluoroquinolones be used sparingly, due to potential resistance concerns. Most forms of CAP stabilize following antibiotic treatment for 2 to 6 days, although several weeks may be required for all symptoms to resolve. Thus, patients with CAP who are cared at home should be reviewed after 48 hours (or earlier if clinically indicated); those failing to show improvement at this time should be considered for hospital admission or chest radiography.


Take home messages

  1. Community acquired pneumonia (CAP) is a common encounter in the primary care setting; often, these patients are hospitalized unnecessarily.
  2. Risk stratification is key towards determining if outpatient or inpatient treatment is necessary.
  3. The CURB-65 and PSI are the two most commonly used clinical prediction results; however, they should not overrule good clinical judgement.
  4. Most current guidelines recommend initial empirical monotherapy; local patterns of disease resistance should be taken into account if possible.

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