Impact of a nudge-based intervention on hand soap usage in a Japanese Hospital: interrupted time series analysis

This study aimed to evaluate the effectiveness of nudge-based messages on hand soap usage in a Japanese hospital setting.

Interrupted time series analysis was conducted using monthly hand soap usage data from April 2022 to March 2024. The following nudge messages were placed in restrooms: "Are your neighbors washing their hands with soap?" (men) and "Water does not disinfect; soap works!" (women). A generalized least squares model with harmonic terms was used to analyze the data, accounting for seasonality and autocorrelation.

The intervention was associated with an immediate increase of 147.85 units/month in hand soap usage (95% confidence interval [CI]: 61.87-233.83; P = 0.003). However, usage gradually decreased by 11.47 units/month thereafter (95% CI: -27.10 to 4.15; P = 0.166). Sensitivity analysis using Poisson regression confirmed the robustness of these findings. The intervention was associated with a 38.5% increase in hand soap usage (incidence rate ratio [IRR] = 1.385, 95% CI: 1.265-1.515, P < 0.001), but there was a subsequent 1.9% monthly decrease (IRR = 0.981, 95% CI: 0.965-0.997, P = 0.019).

These findings suggest that nudge-based interventions can be effective in promoting hand hygiene in Japanese health-care settings, but the effect may wane over time.