A cost-benefit analysis of using wastewater monitoring to guide typhoid vaccine campaigns.

INTRODUCTION: Enteric diseases are a leading cause of mortality in developing countries, yet are highly preventable. Typhoid vaccines remain underutilized, and diagnostic capacity constraints impede treatment and prevention. Wastewater monitoring could provide a more accurate picture of disease burden if detection and quantification of Salmonella Typhi in wastewater are advanced. To motivate why countries should invest to improve wastewater testing methods, we conducted a cost-benefit analysis, quantifying the value this approach could yield. METHODS: We estimated benefits that could accrue if wastewater data informed the early launch of a theoretical typhoid vaccine campaign in Cox's Bazar, Bangladesh. After empirically estimating the lead-time advantage of wastewater data over clinical data to flag case upticks, we simulated changes in case counts from a 1- to 14-day early campaign launch, using ordinary differential equation modeling. We quantified benefits resulting from averted cases (from preserved caregiver time, school days, and wages), hospitalizations (from savings to public funds), and deaths (using the value of statistical life). We then calculated how cumulative benefits, costs, and the ratio of the two varied by campaign launch timing scenario over a five-year period. RESULTS: Wastewater concentrations of Salmonella Typhi upticked up to 13 days before case counts. Cumulative benefits varied by year and launch timing. With a 13-day early launch, every $100 spent on wastewater monitoring could yield $295 in societal benefits by year 5. Cumulative benefits roughly equaled cumulative costs with a 5-day early launch and outweighed costs when the campaign was launched even earlier. CONCLUSION: If wastewater data can be advanced to reliably provide early warnings of new typhoid outbreaks, governments could reap large benefits that more than justify spending on program implementation. Our findings could generalize to other high-aid countries that, like Bangladesh, experience routine enteric disease outbreaks and have strong operational networks.