Methods: This is a prospective cohort study performed at 4 US EDs. From November 2013 – April 2014 we enrolled adults who presented to the ED with acute respiratory illness, broadly defined as presence of at least one of the following symptoms within 7 days of ED presentation (cough, shortness of breath, change in sputum production, sinus pain, nasal congestion, rhinorrhea, sore throat, subjective fever or temperature > 38C). We included only those who would meet CDC criteria for antiviral treatment if influenza test resulted positive. Subjects completed a structured symptom questionnaire and received influenza testing with gold-standard PCR. The data was randomly split into a derivation (80%) and validation dataset (20%). Using a stepwise logistic regression, 4 independent variables were selected using the derivation set, and then analyzed using the validation set.
Results: Of 1987 enrolled subjects, 185 (9.3%) had influenza. The derived CDG included symptoms of cough (2 points), headache (1 point), subjective fever (1 point), and triage temperature of > 38 C (1 point) whereby any patient with 3 or greater points should be tested for influenza. In the training set this CDG had a sensitivity of 93% and specificity of 39% for influenza. In the validation set, this CDG had a sensitivity of 92% and specificity of 28%.
Conclusion: We derived and internally validated a highly sensitive CDG to inform influenza testing amongst ED patients who meet CDC treatment recommendations for receiving antiviral treatment during the influenza season (November – April); key symptoms include cough, headache, subjective fever, and documented fever.