Health indifference, symptom reporting, hospitalization, and vaccination: a three-wave longitudinal analysis of the Japan Society and New Tobacco/Infodemic Survey (JASTIS)

Abstract Background Healthcare systems struggle to reach people who are not interested in their health. However, prospective evidence on this orientation, which is termed health indifference, is scarce. We examined whether health indifference was associated with subsequent hospitalization, symptom reporting, chronic condition reporting, and vaccination in a nationwide Japanese panel. Methods We analyzed three annual waves (2021–2023) of the Japan Society and New Tobacco/Infodemic Survey, in which 15,519 of 26,000 baseline participants formed the analytic cohort. Health indifference was measured in 2022 using a study-specific 13-item index (range, 13–52; higher scores indicate greater indifference). The primary outcome was self-reported all-cause hospitalization in the 12 months preceding the 2023 survey. The secondary outcomes were 14 current chronic conditions, 14 past-week symptoms rated as at least somewhat bothersome, an infection-related SARS-CoV-2 composite, COVID-19 vaccination, and influenza vaccination. The models used prespecified 2021 covariates, modified Poisson regression with robust variance, inverse probability of censoring weighting, 20-dataset multiple imputation, and Benjamini-Hochberg correction across 32 outcomes. Results Per 1-SD increase in health indifference, the risk of self-reported hospitalization was 18% lower (adjusted risk ratio [aRR], 0.82; 95% CI, 0.76–0.88) and influenza vaccination was lower (aRR, 0.90; 95% CI, 0.88–0.92). Associations with symptoms were predominantly positive: after false discovery rate correction, eight of 14 were more frequent, including fever (aRR, 1.12; 95% CI, 1.04–1.19), chest pain (aRR, 1.11; 95% CI, 1.05–1.16), and dyspnea (aRR, 1.08; 95% CI, 1.03–1.12), whereas reduced libido was less frequent (aRR, 0.95; 95% CI, 0.92–0.99). Reported conditions were mixed: cancer (aRR, 0.81; 95% CI, 0.73–0.89) and chronic kidney disease (aRR, 0.87; 95% CI, 0.79–0.97) were less frequent, whereas periodontitis (aRR, 1.06; 95% CI, 1.02–1.11) and dental caries (aRR, 1.15; 95% CI, 1.10–1.20) were more frequent. The complete case analysis reproduced hospitalization, influenza vaccination, and six of the eight positive symptom associations. For hospitalization, the E-value was 1.74 for the estimate and 1.54 for the confidence limit closest to the null. Conclusions At the following survey wave, participants with higher scores on the study-specific health-interest index reported lower hospitalization and influenza vaccination and more frequent occurrence of several symptoms, identifying a group for further prospective study but not establishing healthcare avoidance.