Long-term monitoring of SARS-CoV-2 RNA in wastewater of the Frankfurt metropolitan area in Southern Germany

Abstract

Wastewater-based epidemiology (WBE) is a great approach that enables us to comprehensively monitor the community to determine the scale and dynamics of infections in a city, particularly in metropolitan cities with a high population density. Therefore, we monitored the time course of the SARS-CoV-2 RNA concentration in raw sewage in the Frankfurt metropolitan area, the European financial center. To determine the SARS-CoV-2 RNA concentration in sewage, we continuously collected 24 h composite samples twice a week from two wastewater treatment plant (WWTP) influents (Niederrad and Sindlingen) serving the Frankfurt metropolitan area and performed RT-qPCR analysis targeting three genes (N gene, S gene, and ORF1ab gene). In August, a resurgence in the SARS-CoV-2 RNA load was observed, reaching 3 × 10¹³ copies/day, which represented similar levels compared to April with approx. 2 × 10¹⁴ copies/day. This corresponds to a continuous increase again in COVID-19 cases in Frankfurt since August, with an average of 28.6 incidences, compared to 28.7 incidences in April. Different temporal dynamics were observed between different sampling points, indicating local dynamics in COVID-19 cases within the Frankfurt metropolitan area. The SARS-CoV-2 RNA load to the WWTP Niederrad ranged from approx. 4 × 10¹¹ to 1 × 10¹⁵ copies/day, the load to the WWTP Sindlingen from approx. 1 × 10¹¹ to 2 × 10¹⁴ copies/day, which resulted in a preceding increase in these loading in July ahead of the weekly averaged incidences. The study shows that WBE has the potential as an early warning system for SARS-CoV-2 infections and a monitoring system to identify global hotspots of COVID-19.

Figure 1

Graphical representation of the epidemiological data of COVID-19 cases in Germany (black line) and the city of Frankfurt am Main (blue line). The grey area indicates the time of the summer school vacation in the State of Hesse.

Figure 2

(A) Comparison of the results from April and August 2020, bars represent a three week average around the maximum number of cases per 100.000 persons (P), symbols refer to the respective SARS-CoV-2 RNA loads; (B) Correlation between the total load of SARS-CoV-2 gene copies (sum of the loads to both WWTPs) and incidences in Frankfurt am Main (local).

Figure 3

SARS-CoV-2 RNA loads analyzed with RT-qPCR in the influent of the two WWTP, i.e. Niederrad and Sindlingen, and the count of registered COVID-19 cases in the city of Frankfurt (top).

Figure 4

Load of SARS-CoV-2 target genes observed at the sampling point Griesheim and the WWTP Niederrad, respective concentrations of these two sampling points are provided in the Supplementary Information in Figures S.3 and S.5.