We measured SARS-CoV-2 RNA load in raw wastewater in Attica, Greece, by RT-qPCR for the environmental surveillance of COVID-19 for 6 months. The lag between RNA load and pandemic indicators (COVID-19 hospital and intensive care unit (ICU) admissions) was calculated using a grid search. Our results showed that RNA load in raw wastewater is a leading indicator of positive COVID-19 cases, new hospitalization and admission into ICUs by 5, 8 and 9 days, respectively. Modelling techniques based on distributed/fixed lag modelling, linear regression and artificial neural networks were utilized to build relationships between SARS-CoV-2 RNA load in wastewater and pandemic health indicators. SARS-CoV-2 mutation analysis in wastewater during the third pandemic wave revealed that the alpha-variant was dominant. Our results demonstrate that clinical and environmental surveillance data can be combined to create robust models to study the on-going COVID-19 infection dynamics and provide an early warning for increased hospital admissions.

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Since December 2019, COVID-19 has spread rapidly all over the world with considerable morbidity and mortality. SARS-CoV-2 infections are accompanied by the shedding of virus in feces of both symptomatic and asymptomatic individuals, indicating that Wastewater-based Epidemiology (WBE) is an appropriate chemical tool to monitor the number of infections and disease prevalence in a community level. In the current study, SARS-CoV-2 load was measured in influent wastewater from Athens from November 2020 until May 2021. PEG precipitation and Water DNA/RNA Magnetic Bead kit were selected as the concentration and extraction method, respectively. The study timeline is divided in three different phases based on the levels of viral load. On 7th of November 2020, Greek government announced the second strict total lockdown after March 2020. Viral load was stable during December and the first days of January, indicating the effectiveness of lockdown and restrictions. After the announcement of the third lockdown (20th of February) the viral load reached peak levels especially during April (more than 100,000 copies/L from 17th to 20th of April). On May 14th, the end of lockdown was announced, while the number of vaccinations had been increased and the viral load was significantly decreased to approximately 37,000 copies/L.

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