Correlation between SARS-CoV-2 RNA in wastewater and notified COVID-19 cases and intensive care unit admissions in North Rhine-Westphalia, Germany, 2022-2023

Background: Statewide wastewater monitoring of SARS-CoV-2 in North Rhine-Westphalia (NRW), Germany, started in June 2022 to complement routine COVID-19 surveillance during the pandemic. We aimed to estimate the correlation between SARS-CoV-2 RNA in wastewater with COVID-19 notifications and intensive care unit (ICU) admissions between June 2022 and December 2023 in NRW.

Methods: Wastewater samples were collected bi-weekly from fourteen wastewater treatment plants (WWTPs) covering circa 29% of NRW’s population. SARS-CoV-2 RNA concentrations were quantified by RT-qPCR, normalized by WWTP flow and weighted by the number of people connected to the WWTP. We included laboratory-confirmed COVID-19 cases notified as per the Infection Protection Act and cases treated in ICU recorded in the DIVI Intensive Care Register. We compared wastewater concentrations of SARS-CoV-2 to the number of COVID-19 notifications and ICU admissions in all of NRW using correlation and linear regression analysis to determine the correlation (r), temporal alignment and trend comparisons at three phases with different COVID-19 testing policies.

Results: Preliminary results show positive correlations up to r=0.95 between SARS-CoV-2 in wastewater with COVID-19 notifications and ICU admissions, with optimal correlation at no time-offset (0 days). We observed variations in lead and lag time and strength of correlation between wastewater, notification and ICU data over time. Although testing policy influenced testing frequency and thus the number of notifications, SARS-CoV-2 concentrations in wastewater remained stable. Comparing trends showed parallel periods of increases and decreases between wastewater, notification and ICU data.

Conclusions: Wastewater concentrations of SARS-CoV-2 provide a real-time indication of COVID-19 infection dynamics in the population served by the WWTPs. Wastewater monitoring of SARS-CoV-2 could inform the public of current trends and guide public health preparedness strategies, regardless of testing policy.

Publication History

Article published online:
11 March 2025