[Error factors and sustainable utility of COVID-19 wastewater surveillance in Japan]

Objectives　In response to the coronavirus disease 2019 (COVID-19) pandemic, the usefulness of wastewater surveillance has been highlighted. Wastewater surveillance can detect pathogens that circulate throughout society, including asymptomatic infections, thereby allowing early outbreak warnings. However, several error factors must be considered when applying wastewater surveillance for COVID-19. This study examines the key error factors in COVID-19 wastewater surveillance and discusses their future applicability in Japan.Methods　A literature search was conducted using PubMed and Ichushi-Web to review the studies on wastewater surveillance for COVID-19. The search included combinations of the keywords "wastewater," "sewage," "COVID-19," "SARS-CoV-2," "fecal/urine," and "surveillance/survey/detection." A narrative review was conducted based on the search results.Results　A total of 2,108 articles were identified in PubMed, of which 19 were included in this review. In addition, six academic articles were retrieved from Google Scholar, and two government reports and guidelines were included in this review. The sampling methods and environmental factors such as wastewater temperature, transit time, and composition can be potential sources of error in wastewater surveillance. Furthermore, the standardization of these factors is difficult. The prevalence of COVID-19, population size, and population mobility in the target area also influence data interpretation. Additionally, because wastewater surveillance often lacks detailed patient background information such as age, sex, and exact locations of affected individuals, data interpretation can be more challenging than clinical testing-based surveillance, thus potentially limiting its applicability. However, compared to large-scale clinical screening, wastewater surveillance is significantly more cost-effective, rapid, and suitable for continuous monitoring. With regard to statistical analysis, sample normalization is crucial for accurate comparisons across samples, regions, and time periods. A low signal-to-noise ratio during COVID-19 wastewater surveillance requires significant smoothing procedures to extract meaningful signals.Conclusion　Wastewater surveillance for COVID-19 is subject to errors from several sources. Nevertheless, it offers advantages over clinical surveillance that include lower expected costs and capacity for continuous monitoring across broad geographic areas. In conclusion, it is essential to understand the advantages and limitations of both clinical and wastewater surveillance and appropriately integrate both approaches for optimal utilization.