Predictors of pneumonia in lower respiratory tract infections: 3C prospective cough complication cohort study.

The aim was to aid diagnosis of pneumonia in those presenting with lower respiratory tract symptoms in routine primary care. A cohort of 28 883 adult patients with acute cough attributed to lower respiratory tract infections (LRTIs) was recruited from 5222 UK practices in 2009-13. Symptoms, signs and treatment were recorded at presentation and subsequent events followed-up for 30 days by chart review. The predictive value of patient characteristics, presenting symptoms and clinical findings for the diagnosis of pneumonia in the first 7 days was established. Of the 720 out of 28 883 (2.5.%) radiographed within 1 week of the index consultation, 115 (16.0%; 0.40% of 28 883) were assigned a definite or probable pneumonia diagnosis. The significant independent predictors of radiograph-confirmed pneumonia were temperature > 37.8 degrees C (RR 2.6; 95% CI 1.5-4.8), crackles on auscultation (RR 1.8; 1.1-3.0), oxygen saturation < 95% (RR 1.7; 1.0-3.1) and pulse > 100 u min-1 (RR 1.9; 1.1-3.2). Most patients with pneumonia (99/ 115, 86.1%) exhibited at least one of these four clinical signs; the positive predictive value of having at least one of these signs was 20.2% (95% CI 17.3-23.1). In routine practice, radiograph-confirmed pneumonia as a short-term complication of LRTI is very uncommon (one in 270). Pulse oximetry may aid the diagnosis of pneumonia in this setting.