“The isolation of the viral RNA from wastewater indicates that parts of the genetic material of the SARS-CoV-2 coronavirus are present in the sewage system, which confirms that infected people discharge the virus through their faeces and other excretions into sewage,” the HZJZ said on the occasion of World Water Day, observed on 22 March.
The HZJZ tested wastewater in Zagreb in collaboration with the Zagrebačke Otpadne Vode wastewater company and the Croatian Office of the World Health Organisation. The project was carried out from 1 December 2020 to 18 February 2021 and was financed by the German government.
The testing results indicate that the viral load of wastewater is in correlation with the number of active cases of coronavirus infection in the city. The number of active cases in Zagreb was 3,913 in early December, dropping to below 1,000 by the end of that month.
The number of copies of the viral RNA was considerably higher in the first half of December, decreasing by the end of the month. The decrease correlated with stricter epidemiological measures that were imposed between 28 November and 21 December, the HZJZ said.
The number of active coronavirus cases in January 2021 ranged from 1,113 to 318, when a drop in the number of copies of the viral genome were recorded in wastewater samples. The low number of copies of the viral genome was also found in February 2021 when the number of active cases in Zagreb ranged from 434 to 280.
The HZJZ noted that the wastewater in the sewage system is affected by precipitation which dilutes it, which is why a low number of copies of the viral genome was observed in days with considerable precipitation.
It also pointed out that the proof of the presence of the viral RNA does not prove the viability of the virus, but that tests like this can be used to monitor trends and provide an early warning of the virus circulating in the population.
After 18 February, wastewater sampling has continued once a week in accordance with the European Commission’s recommendation on monitoring the coronavirus in wastewater.
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