Analysis of SARS-CoV-2 monitoring results in sewage in Shandong province, 2024: based on sewage sample monitoring

Objective To understand the epidemic trend of SARS-CoV-2 and explore the practical significance of sewage monitoring in the assessment and prevention of COVID-19 epidemic by analyzing the monitoring data of SARS-CoV-2 in sewage in Shandong province.

Methods In 2024, a total of 9 464 sewage samples from the main urban sewage treatment plants in 16 cities of Shandong province were collected weekly. The positive rate and the weighted average concentration of SARS-CoV-2 in the samples were continuously monitored. Correlation analysis was conducted between the weekly positive rates and weighted average concentrations across the province. On the basis of the data such as the weighted average concentration, the weekly number of SARS-CoV-2 infections was estimated. Correlation analysis was then performed between the estimated infection number and the reported cases of SARS-CoV-2 infection in Shandong province.

Results In 2024, a total of 9 464 sewage samples were monitored in Shandong province. The average positive rate of SARS-CoV-2 in the wastewater throughout the year was 46.91%, and the average weighted average concentration was 11.69 copies/mL. The positive rate and weighted average concentration of SARS-CoV-2 in the sewage samples in Shandong province showed two peaks. The first peak occurred from the 1st week to the 24th week (January to June), with the highest positive rate of 77.72% and the highest weighted average concentration of 42.27 copies/mL. The second peak occurred from the 29th week to the 46th week (July to November), with the highest positive rate of 67.36% and the highest weighted average concentration of 19.7 copies/mL. The positive rate and weighted average concentration throughout the province had a high correlation (r = 0.888 7, P < 0.001, 95%CI: 0.812 9–0.934 9). The positive rates varied among different cities (χ² = 2 233, P < 0.001), ranging from 14.58% to 89.58%. The weighted average concentrations ranged from 0.81 to 46.76 copies/mL. The number of reported SARS-CoV-2 infection cases in Shandong province ranged from 117 to 5 864, and the trend of increase or decrease in the number of reported cases over time was consistent with the changes in positive rate and weighted average concentration of SARS-CoV-2 in sewage. The estimated number of infections throughout the year ranged from 52 to 2 277, and there was a correlation between the estimated infection number and the number of reported cases (r = 0.769 9, P < 0.001, 95%CI: 0.629 2–0.861 8).

Conclusions The positive rate and concentration changes of SARS-CoV-2 in sewage in Shandong province, 2024 are basically consistent with the variations in the number of reported cases. There is a certain correlation between the estimated infection number and the number of reported cases. The monitoring results of sewage can to some extent reflect the infection situation of the population.