Sars-CoV-2 viral load in wastewater and its association with ambient temperature in the Athens, Greece, area

Background: Measurements of SARS-CoV-2 viral load in wastewater represents an objective assessment of the viral load in a population as it does not suffer from selection bias. The objective of this study was to evaluate the role of ambient temperature in the spread of COVID-19 in the Athens by using data from the wastewater viral load. Methods: Data on the daily SARS-CoV-2 viral load (copies/100,000 inhabitants), ambient temperature, public health control measures for COVID -19 (as expressed by sector-specific mobility data) were obtained on a daily basis from 31 August 2020 to 14 October 2021. Distributed lag non-linear regression models were applied with log-transformed viral load as dependent variable. Separate lags were alternatively investigated. Twenty four hour temperature was used as main exposure, adjusting for mobility data and particulate matter pollution. Solar radiation and relative humidity were also used. Results: There was an indication of an association of higher ambient temperature with an increase in the viral load, which became apparent after 3 days but did not always reach the nominal level of statistical significance. The association with daily PM10 concentrations was also not statistically significant. However, a statistically significant positive association was observed between viral load and retail/ recreation mobility. Conclusions: The variability of viral load in wastewater appears to be dominated by public health control measures resulting to changes in mobility and the mean number of contacts within the population. The role of ambient temperature is not clear. The potential effect of ambient temperature was probably modified by changes in virus transmissibility during the emergence of variants of concern dominating in different time periods. In our setting, statistical power may have been limited by the relatively short period of data availability. Key words: COVID-19, wastewater viral load, ambient temperature