(286) Accuracy of ICD-10 Diagnosis Codes for Identifying Influenza Illness Among Children in the Emergency Department and Hospital Settings

Publication Number: 944

Background: Real world evidence studies of influenza illness in children commonly rely on coded diagnosis to identify those events. Yet, the ability of previously used ICD-9 diagnosis codes to identify influenza in the pediatric emergency department (ED) and inpatient settings were highly variable with a wide range of reported positive predictive values [PPV 55-91%]. Nevertheless, the accuracy of the newer, currently used ICD-10 codes to identify influenza illness in children in those settings is unknown.

Objectives: To determine the accuracy of ICD-10 influenza diagnosis codes in pediatric ED and inpatient settings using laboratory-confirmed testing as the gold standard diagnostic in an active population-based surveillance system

Methods: Data were obtained from the Centers for Disease Control and Prevention’s New Vaccine Surveillance Network, a population-based, year-round, surveillance of acute respiratory illnesses (ARI). Individuals < 18 years presenting to the ED or inpatient setting with fever and/or respiratory symptoms at seven pediatric medical centers between Dec 11, 2016 and Feb 23, 2020 were included. Nasal and/or throat swabs were collected for research molecular testing for influenza, regardless of clinical testing performed. True influenza cases were defined as either a positive research or clinical influenza test. Influenza seasons were defined by site as spanning the first through last weeks with 2 positive surveillance tests. The accuracy of ICD-10 coded diagnoses was calculated using the laboratory test results as reference. Measurements included sensitivity, specificity, positive and negative predictive value (NPV). Estimates were stratified by setting (ED vs inpatient) and age (0-1, 2-4, 5-17 years).

Results: A total of 16,452 children in ED (median age 2.0 y, IQR 0-4) and 16, 516 from the inpatient setting (Median age 1.0 y, IQR 0-4) were included. In the ED, ICD-10 influenza diagnoses were highly specific (0.99) and had high PPV (0.94), whereas their sensitivity and NPV were 0.48 and 0.92 respectively. In the inpatient setting, the codes specificity was 0.996 and the PPV was 0.92, whereas the sensitivity and NPV were 0.35 and 0.95 respectively. PPV was lowest in the 0-1 y (ED: 0.90, Inpatient: 0.81) and similar in ages 2-4 and 5-17 (ED: 0.95, 0.96, inpatient: 0.90, 0.91).

Conclusions: Influenza ICD-10 diagnoses are highly specific in identifying laboratory-confirmed influenza illness in the ED and hospital settings, but their sensitivity is modest. There are age-based and care location differences in accuracy of ICD-10 influenza diagnoses. These findings may aid assessment of misclassification of influenza diagnoses. Future efforts should focus on improving identification of influenza in young, hospitalized children using real world data.