Development and External Validation of the FluScoreVax Risk Score for Influenza That Incorporates Vaccine Status

To develop and externally validate a simple risk score for influenza diagnosis based using vaccination history and patient-reported symptoms.

Adult outpatients in 12 European countries during flu season with a chief complaint of acute cough between 2007 and 2010 were used to derive and internally validate the risk score (Genomics to combat Resistance against Antibiotics in Community acquired LRTI in Europe (GRACE) data), and contemporary US data were used for external validation (EAST-PC data). Patient-reported symptoms were recorded and polymerase chain reaction (PCR) was used to diagnose influenza. The score was derived using logistic regression and assigning points based on the β -coefficients. The score was externally validated in a contemporary US population (EAST-PC data). Accuracy was measured using influenza prevalence in each risk group and the area under the receiver operating characteristic curve (AUC). Calibration was assessed by plotting observed versus expected.

We developed a risk score with 6 items (subjective fever, interfered with usual activity, headache, wheeze, phlegm, and recent flu vaccine) and a range from -5 to 6 points. The AUC was 0.75 for both derivation and internal validation subgroups. The prevalence of influenza was 15.1% in the GRACE data and 14.4% in the EAST-PC data. The percentage with influenza in the low, moderate, and high-risk groups was 6.8%, 21.8%, 35.3 in the external validation population (EAST-PC data). The low-risk group included 61% of participants in the external validation. Calibration was excellent.

We developed and externally validated the FluScoreVax risk score, available as an app. It classifies 61% of patients as low risk, of whom only 7% had influenza.