ILLUSTRATIVE CASE
An otherwise healthy 56-year-old woman presents to the emergency department (ED) with a productive cough of 4 days’ duration. A review of her history is negative for recurrent upper respiratory infections, smoking, or environmental exposures. Her physical exam is unremarkable and, more specifically, her pulmonary exam and vital signs (temperature, respiratory rate, and heart rate) are within normal limits. The patient states that last year her friend had similar symptoms and was given a diagnosis of pneumonia. Is it necessary to order a chest x-ray in this patient to rule out community-acquired pneumonia (CAP)?
CAP is a common pulmonary condition seen in the outpatient setting in the United States, representing more than 4.5 million outpatient visits in the years 2009 to 2010.2 Historically, a diagnosis of CAP has been based on clinical findings in conjunction with infiltrates seen on chest x-ray.
In 2017, more than 5 million visits to the ED were due to a cough.3 The use of radiographic imaging in EDs has been increasing. There were 49 million x-rays and 2.7 million noncardiac chest computed tomography (CT) scans performed in 2016, many of which were for patients with cough.3,4 Although imaging is an extremely useful tool and indicated in many instances, the ability to rule out CAP in an adult who presents with a cough by using a set of simple, clinically based heuristics without requiring imaging would help to increase efficiency, limit cost, and decrease exposure of patients to unnecessary and potentially harmful diagnostic studies.
Clinical decision rules (CDRs) are simple heuristics that can stratify patients as either high risk or low risk for specific diseases. Two older large, prospective cross-sectional studies developed CDRs to determine the probability of CAP based on symptoms (eg, night sweats, myalgias, and sputum production) and clinical findings (eg, temperature > 37.8 °C [100 °F], tachypnea, tachycardia, rales, and decreased breath sounds).5,6 This meta-analysis includes these studies and more recent studies7-9 used to develop a CDR that focuses solely on a few specific signs and symptoms that can reliably rule out CAP without imaging, and so prove highly useful for busy primary care clinicians.
STUDY SUMMARY
This simple approach rules out CAP in outpatients 99.6% of the time
This systematic review and meta-analysis included studies that used 2 or more signs, symptoms, or point-of-care tests to determine the patient’s risk for CAP.1 Twelve studies (N = 10,254) met inclusion criteria by applying a CDR to adults or adolescents presenting with respiratory signs or symptoms potentially suggestive of CAP to either an outpatient setting or an ED. Prospective cohort, cross-sectional, and case-control studies were included when a chest x-ray or CT was utilized as the primary reference standard. Exclusion criteria included studies of military or nursing home populations and studies in which the majority of patients had hospital- or ventilator-associated pneumonia or were immunocompromised.
A simple, highly useful CDR emerged from 3 of the studies (N = 1865).7-9 Two of these studies were described as case-control studies with prospective enrollment of patients older than 17 years in both outpatient and ED settings.7,8 One study was conducted in the United States (mean age, 65 years) and the other in Iran (mean age, 60 years). The third was a Chilean prospective cohort study of ED patients older than 15 years (mean age, 53 years).9 In each of these studies, the outpatient or ED physicians collected all clinical data and documented their physical exam prior to receiving the chest radiograph results. The radiologists were masked to the clinical findings at the time of their interpretation.
Results. From the meta-analysis, a simple CDR emerged for patients with normal vital signs (temperature, respiratory rate, and heart rate) and a normal pulmonary exam that virtually ruled out CAP (sensitivity = 96%; 95% CI, 92%–98%; and negative likelihood ratio = 0.10; 95% CI, 0.07–0.13). In patients presenting to an outpatient clinic with acute cough with a 4% baseline prevalence rate of pneumonia, this CDR ruled out CAP 99.6% of the time.
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