Wastewater based epidemiology as a complementary decision-making tool

To assist public health authorities in recommending interventions against the spread of COVID-19 or, conversely, loosening protective measures, at minimum cost in human lives and the economy, reliable large scale early warning methods are required. Medically confirmed cases are not sufficient to provide strong early warning signs because only cases of infected patients are reported when they are found. In addition, clinical tests, practically targeting small parts of the population may fail to reveal the true scale of the epidemic and set off alarms, since there are likely many more patients in the community than the identified ones.
Estimating the spread of SARS-CoV-2 through its load in sewage was applied in Thessaloniki as an early warning tool. To this regard, 24-h composite samples were collected every day at the entrance of the wastewater treatment plant of the city and were subsequently subjected to molecular analysis, to quantitatively determine the SARS-CoV-2 viral load. However, viral load itself is not an accurate index of the load circulated in the community as it is strongly affected by environmental factors, e.g., suspended solids present in wastewater adsorb the virus masking its real concentration.
To this respect, a physicochemical model that can rationalize the quantitative measurements of viral genome was developed and successfully applied. Results are submitted to the National Health Organization and the Ministry of Health and announced in media.