The relationship between seasonal influenza and telephone triage for fever: A population-based study in Osaka, Japan

BACKGROUND: Replacing traditional surveillance with syndromic surveillance is one of the major interests in public health. However, it is unclear whether the number of influenza patients is associated with the number of telephone triages in Japan. METHODS: This retrospective, observational study was conducted over the six-year period between January 2012 to December 2017. We used the dataset of a telephone triage service in Osaka, Japan and the data on influenza patients published from the Information Center of Infectious Disease in Osaka prefecture. Using a linear regression model, we calculated Spearman’s rank-order coefficient and R(2) of the regression model to assess the relationship between the number of telephone triages for fever and the number of influenza patients in Osaka. Furthermore, we calculated Spearman’s rank-order coefficient and R(2) between the predicted weekly number of influenza patients from the linear regression model and the actual weekly number of influenza patients for influenza outbreak season (December-April). RESULTS: There were 465,971 patients with influenza, and the number of telephone triages for fever was 420,928 among 1,065,628 total telephone triages during the study period. Our analysis showed that the Spearman rank-order coefficient was 0.932, and R(2) and adjusted R(2) were 0.869 and 0.842, respectively. The Spearman rank-order coefficient was 0.923 (P<0.001) and R(2) was 0.832 in December-April (P<0.001). CONCLUSION: We revealed a positive relationship in this population between the number of influenza patients and the number of telephone triages for fever.