Acute cough is one of the most common symptoms managed in primary care. The vast majority of patients presenting with cough suffer from an uncomplicated (presumably viral) lower respiratory tract infection (LRTI), but a considerable proportion are prescribed antibiotics for suspected pneumonia. Most of these prescriptions are unnecessary or even harmful, but discriminating pneumonia from uncomplicated LRTI on clinical grounds alone is not trivial. To shed light on this issue, investigators have conducted a prospective cohort study involving 28,883 adult patients with acute cough attributed to LRTI who were recruited from 5,222 practices in the U.K. between 2009 and 2013. Of this cohort, 720 (2.5%) had a chest x-ray taken within the first 7 days. Those referred for chest x-ray were sicker, older, more likely to be smokers, and more likely to have physical signs indicating pneumonia. Results were as follows:
- Chest x-rays showed a definite or probable diagnosis of pneumonia in 115 (16.0%; 0.4% of 28,883).
- Significant independent predictors of x-ray–confirmed pneumonia were temperature >37.8°C, crackles on auscultation, oxygen saturation <95%, and heart rate >100/min.
- 86% of patients with pneumonia exhibited at least one of these four clinical signs (positive predictive value, ≥20%).
- Positive predictive value increased to 57% if all four criteria were met, but with low sensitivity (3.5%).
- Presenting symptoms (including shortness of breath, confusion, and sputum color) did not provide diagnostic information for discriminating pneumonia from LRTI.
- This large study shows that x-ray–confirmed pneumonia is uncommon among patients with acute cough in primary care. The best parameters for distinguishing pneumonia from other LRTI are physical examination along with oxygen saturation measurement.