The outbreak of the Covid-19 pandemic brought to the fore the need for timely detection, prediction and prevention method for infectious diseases. Wastewater-based epidemiology (WBE) was proposed as a complementary method, an early warning, to track pathogens that are causing infections into the community, in order, the Healthcare systems to take timely measures. The epidemiological surveillance of urban wastewater is now a practice recommended by the European Commission and the World Health Organization (WHO) considered as a complementary method to clinical approach, for COVID-19 surveillance. It can provide important information to Public Health decision-making process helping governments mitigate the health and socioeconomic consequences of outbreaks (Xagoraraki & O’Brien, 2020; World Health Organization, 2022).
COVID-19 first cases were reported in Greece on 26 February 2020. Regarding the multitude of confirmed cases and deaths, during the years 2020–2022 by the infection from SARS-CoV-2, circulation of the virus in the community needed continuous and rapid detection (Kousi et al., 2021).
Although SARS-CoV-2 (Severe Acute Respiratory Syndrome Coronavirus 2) is a pathogenic virus that infects the respiratory system, it has also been documented to infect the gastrointestinal tract, resulting in excretion through the feces into the sewage system. Many studies have reported gastrointestinal symptoms in patients with COVID-19 such as diarrhea, vomiting, anorexia and abdominal pain (Guo et al., 2021). Even if there are no gastrointestinal symptoms, the elimination of viral particles is already starting from the beginning of the infection, therefore, they can be detected before the onset of the symptoms of the infection. In addition, asymptomatic carriers shed viral particles, without showing clinical symptoms (Daughton 2018; Agrawal et al. 2021) and seems to persist longer, about 3 weeks, in the stool than in the respiratory system, as it is recorded in many samples of COVID-19 confirmed cases (Zhang et al., 2021; Chen et al., 2020; Park et al., 2021; Cho & Ha, 2020; Xu et al., 2020). Hence, it is recorded that both asymptomatic and symptomatic individuals, even after recovery from the symptoms, can shed significant copies of SARS-CoV-2 RNA in their feces (Mizumoto et al., 2020; Nishiura et al., 2020; Treibel et al., 2020; Wu et al., 2020). Wastewater samples showed a correlation between SARS-CoV-2 RNA concentrations and the number of COVID-19 clinical cases in many studies (Ahmed et al., 2020; Medema et al., 2020; Peccia et al., 2020). Municipal sewage is sampling material from a wide range of population and mainly healthy population, which would otherwise not be possible to monitor, independent of people’s socioeconomic status or ability to have access to healthcare (Sharara et al. 2021). Furthermore, analysis of wastewater samples, is a non-invasive method, it does not require informed consent, thus, limiting ethical and bioethical concerns (Choi et al., 2018; Anand et al., 2021). As a result, WBE gives us a complete and reliable picture of the prevalence of SARS-CoV-2 virus, disease spread can be monitored, and the effectiveness of public health interventions can be evaluated.
The number of studies reporting the detection of SARS-CoV-2 RNA in wastewater is ever increasing and nowadays, WΒΕ has been established, across Europe, as an efficient, fast and reliable source of epidemiological information for national health authorities, local healthcare, national disease control centers, private wastewater operators, and water and environment agencies (Monteiro et al., 2022; Maida et al., 2022). Subsequently, networks have been established for the exchange of information, methods and results for the purpose of comparability, evaluation, and assessment of methods aiming at more effective and reliable epidemiological surveillance. (https://score-network.eu/) (Publication Map | covid19wbec.org)
Urban wastewater is a complex matrix that includes suspended solids, a variety of organic and inorganic chemicals, pharmaceuticals, metabolites, detergents, small-scale toxic wastes, nutrients, pathogenic microorganisms, and other substances (Balboa et al., 2021). The great diversity of chemical and biological elements contained in wastewater lead to various obstacles in terms of wastewater analysis, for this reason, the physicochemical characteristics of the wastewater must also be taken into account since they can cause inhibition of the viral detection procedure (Bivins et al., 2021). However, inhibition can be limited by the use of good laboratory practices, appropriate selection of the genetic material isolation procedure and purification of the isolate. Furthermore, questions arise as how much the concentration of the viral RNA can affect the physicochemical characteristics of the wastewater and if certain of them can be additional indicators of the increase of viral load.
Additionally, the effect of weather conditions, such as rainfall and average and/or maximum day temperature, on the concentration of the virus in wastewater has not yet been thoroughly investigated.
In Greece, at the beginning of 2021, the National Public Health Organization (EODY) created the National Wastewater Epidemiology Network, for the monitoring, recording and early warning of the spread of the SARS-CoV-2 virus in the community, which is now active on a daily basis in the 5 largest cities of Greece, including Patra. In this study, in the framework of the aforementioned project, the aim was to establish a WBE surveillance system for SARS-CoV-2 in the city of Patras. To assess two RNA recovery methods based on quantitative PCR assays, to monitor the presence and course of the epidemic, to evaluate the influence of weather conditions on viral load and the correlation with certain physicochemical characteristics with the prospect of extending surveillance knowledge.