Economic evaluation of the city-level warning system based on surveillance at wastewater treatment plants to recommend optimal clinical COVID-19 screening tests at long-term care facilities, Japan

The COVID-19 pandemic continues to impose substantial burdens on vulnerable subpopulations such as long-term care facility (LTCF) residents. Our previous simulation study found that the economic efficiency of clinical screening tests (for asymptomatic individuals) at a single LTCF could be maximized if an optimal screening timing is triggered by city-level incidence. City-level incidence could be estimated by conventional "clinical surveillance" based on routine diagnostic tests for symptomatic patients visiting medical institutions. The current study's objective was to evaluate how the addition of "wastewater surveillance conducted at treatment plants (WSTPs)" to our hypothetical warning system (based on clinical surveillance as status quo) could improve the economic efficiency of clinical screening tests at "multiple LTCFs in a city" by recommending clinical screening tests to be initiated at LTCFs on a timelier basis. We performed cost-benefit analyses (CBAs), developing standard decision models with parameters assumed from the literature. CBAs' benefits included related health expenditure and quality-adjusted life-years (QALYs) saved, assuming a $35,234 (¥5 million)-per-QALY willingness-to-pay threshold. CBAs estimated return-on-investment (ROI, equivalent to benefit-to-cost ratio) and net-benefits (in 2024 US dollars) of our warning system at a single LTCF and at city and national levels in Japan, implementing clinical screening tests for all residents and staff members at LTCFs (N = 160-0.27 million). Our simulation results indicated that the addition of WSTPs is highly likely to generate incremental net-benefit of the proposed warning system, e.g., $172,000 at a single LTCF and $3.5-$41 million at the national level, during four weeks with a high incidence of COVID-19 infection. Estimates of ROI and net-benefits were generally robust, although it should be noted that they were sensitive to incidence and LTCFs' compliance to a warning. In conclusion, these findings specify the potential benefit of our proposed city-level warning system, generating net-benefit when combined with WSTPs for COVID-19.