Point-of-Care Guides

Community-Acquired Pneumonia: Determining Safe Treatment in the Outpatient Setting


Am Fam Physician. 2019 Jun 15;99(12):768-769.

Author disclosure: No relevant financial affiliations.

Clinical Question

When is it safe to treat a patient with community-acquired pneumonia (CAP) as an outpatient?

Evidence Summary

Some patients with CAP can be treated safely as outpatients. Several clinical prediction rules have been developed to determine the likelihood of mortality in patients with CAP, and the use of these rules is recommended by practice guidelines to support clinician decision-making. For example, the 2007 guidelines from the Infectious Diseases Society of America and American Thoracic Society note that the Pneumonia Severity Index and the CURB-65 (confusion, uremia, respiratory rate, blood pressure, 65 years of age) rule can help identify patients with CAP who are candidates for outpatient therapy.1 The 2009 guidelines from the British Thoracic Society recommend use of the CURB-65 rule for patients evaluated in the emergency department and the CRB-65 rule for patients evaluated in the primary care or community setting.2

The Pneumonia Severity Index (https://www.mdcalc.com/psi-port-score-pneumonia-severity-index-cap) has been developed and validated in hospital-based settings.3,4 However, the rule has 20 data elements, and a chest radiograph and several blood tests, such as arterial blood gas, are required. Even in the emergency department setting where these tests are readily available, the number of data elements makes the Pneumonia Severity Index difficult to use in real-world practice.

The CURB-65 (https://www.mdcalc.com/curb-65-score-pneumonia-severity) has only five data elements, is accurate, and has been well validated.5 However, it requires blood urea nitrogen testing, which is not readily available in the outpatient primary care setting. The CRB-65 is identical to the CURB-65, except that it does not require a blood urea nitrogen measurement, and has also been well validated in the primary care setting. A recent meta-analysis of the CRB-65 found an overall area under the receiver operating characteristic curve of 0.74 (good discrimination); a ratio of observed to expected mortality of 1.04 (good calibration); and likelihood ratios for mortality of 0.13, 1.3, and 5.6 for low-, moderate-, and high-risk groups, respectively. The meta-analysis was limited to the eight studies judged to be at low risk of bias in which patients could be treated as outpatients or inpatients.6

Because it has only four data elements and does not require blood tests or a radiograph, the CRB-65 is the best choice for risk stratification in the outpatient primary care setting. In two European studies, the overall mortality was 4% in patients with CAP presenting in the outpatient primary care setting who could be treated as inpatients or outpatients.5,7  Applying the likelihood ratios to this baseline risk of mortality, the mortality rate for patients at low, moderate, and high risk based on the CRB-65 rule is shown in Table 1.57

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CRB-65 Rule to Predict Mortality in Patients with Community-Acquired Pneumonia

Step 1: Calculate the score (range 0 to 4 points)

Sign or symptom


Confusion (new onset with this illness)


Respiratory rate ≥ 30 breaths per minute


Blood pressure < 90 mm Hg systolic or ≤ 60 mm Hg diastolic


65 years or older




Step 2: Apply the score to a patient with community-acquired pneumonia

Risk group (points)

Likelihood ratio for mortality

Mortality rate (%)*

Clinical recommendation

Low (0)



Outpatient treatment unless otherwise contraindicated

Moderate (1 or 2)



Hospitalize in most cases

High (3 or 4)



Hospitalize, and consider intensive care unit

*—Assuming an overall mortality rate of 4%.

Information from references 57.


CRB-65 Rule to Predict Mortality in Patients with Community-Acquired Pneumonia

Step 1: Calculate the score (range 0 to 4 points)

Sign or symptom



Address correspondence to Mark H. Ebell, MD, MPH, at ebell@uga.edu. Reprints are not available from the author.

Author disclosure: No relevant financial affiliations.


show all references

1. Mandell LA, Wunderink RG, Anzueto A, et al. Infectious Diseases Society of America/American Thoracic Society consensus guidelines on the management of community-acquired pneumonia in adults. Clin Infect Dis. 2007;44(suppl 2):S27–S72....

2. Lim WS, Baudouin SV, George RC, et al. BTS guidelines for the management of community acquired pneumonia in adults: update 2009. Thorax. 2009;64(suppl 3):iii1–55.

3. Fine MJ, Auble TE, Yealy DM, et al. A prediction rule to identify low-risk patients with community-acquired pneumonia. N Engl J Med. 1997;336(4):243–250.

4. Aujesky D, Fine MJ. The pneumonia severity index: a decade after the initial derivation and validation. Clin Infect Dis. 2008;47(suppl 3):S133–S139.

5. Bauer TT, Ewig S, Marre R, Suttorp N, Welte T; CAPNETZ Study Group. CRB-65 predicts death from community-acquired pneumonia. J Intern Med. 2006;260(1):93–101.

6. Ebell MH, Walsh M, Fahey T, Kearney M, Marchello C. Meta-analysis of calibration, discrimination, and stratum-specific likelihood ratios for the CRB-65 score [published ahead of print April 16, 2019]. J Gen Intern Med. https://link.springer.com/article/10.1007%2Fs11606-019-04869-z. Accessed May 7, 2019.

7. Krüger S, Ewig S, Marre R, et al.; CAPNETZ Study Group. Procalcitonin predicts patients at low risk of death from community-acquired pneumonia across all CRB-65 classes. Eur Respir J. 2008;31(2):349–355.

This guide is one in a series that offers evidence-based tools to assist family physicians in improving their decision-making at the point of care.

This series is coordinated by Mark H. Ebell, MD, MS, Deputy Editor for Evidence-Based Medicine.

A collection of Point-of-Care Guides published in AFP is available at https://www.aafp.org/afp/poc.



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