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SARS-CoV-2 detection in wastewater as an early warning: the case of metropolitan area of the city of Buenos Aires (AMBA).

Agua y Saneamientos Argentinos S.A. (AySA) delivers essential services as drinking water production and wastewater treatment for more than 14.5 million inhabitants of Buenos Aires Metropolitan Area (AMBA), Argentina, and collects residual liquids of 8.5 million through 16,178 km network. Since the very moment the World Health Organization (WHO) declared the COVID-19 pandemic, AySA developed a methodology to determine SARS- CoV-2 viral genetic load in untreated wastewater as an epidemiological surveillance tool, based on international experiences. In order to monitor viral load in the representative areas of the sewage collection system, more than 1500 samples where concentrated, by using an adapted ultracentrifugation method followed by RNA extraction and quantitative reverse transcription polymerase chain reaction (RT-qPCR), to measure the target Orf1ab gene of SARS-CoV-2 in our molecular microbiology laboratory. This research was developed for a period that lasted from January 01 to June 02, 2021, in order to anticipate to the current second wave. The results achieved have demonstrated that changes in SARS-CoV-2 RNA are satisfactorily related to local epidemiological data for COVID-19. The association of variables is statistically significant when analyzing data from four large wastewater treatment plants, (R2 > 0.5 and p-value < 0.05), obtaining significant correlations between log10 viral genomic load and log10 positive cases reported one and two weeks later after samples were analyzed. From the results obtained, it is concluded that the virus sewage system levels were a good predictor of clinical cases to be diagnosed in the immediate future and it is feasible to use this methodology, at local level, as an additional tool for decision-making in public health strategy.