key: cord-287256-hgqz1bcs
authors: Magurano, Fabio; Baggieri, Melissa; Marchi, Antonella; Rezza, Giovanni; Nicoletti, Loredana
title: SARS-CoV-2 infection: the environmental endurance of the virus can be influenced by the increase of temperature
date: 2020-11-05
journal: Clin Microbiol Infect
DOI: 10.1016/j.cmi.2020.10.034
sha: 
doc_id: 287256
cord_uid: hgqz1bcs

Objectives The goal of the current study is to evaluate whether the increase of temperature can influence the environmental endurance of SARS-CoV-2. Methods The virus was inoculated on plastic surface and harvested at predefined time-points in parallel at 20-25°C (RT) and at 28°C (JT). Samples collections were tested by TCID50 titers on Vero cells. Samples collections were tested by TCID50 titers on Vero cells. Results Our results confirm that fomite transmission of the emerging SARS-CoV2 is possible: the virus reserved its ability to infect cells up to 84 hours at both RT and JT on plastic surface, with a TCID50 viral titre of 0,67 and 0,25 log10 respectively. At RT, an important reduction in the viral titre, from 4 log10 to 3 log10 TCID50 was observed during the first 24-36 hours. At JT the same decay was observed more rapidly (between 8 and 12 hours), The rate of viral inactivation by D-value was 24.74 at RT and 12,21 hours at JT. Conclusions This remarkable difference between the two temperatures suggests that virus vitality can be influenced by the environmental temperature and that the hot season could reduce the probability of COVID-19 transmission.

Objectives. The goal of the current study is to evaluate whether the increase of temperature can influence the environmental endurance of SARS-CoV-2.

parallel at 20-25°C (RT) and at 28°C (JT). Samples collections were tested by TCID 50 titers on Vero cells. Samples collections were tested by TCID 50 titers on Vero cells.

Our results confirm that fomite transmission of the emerging SARS-CoV2 is possible: the virus reserved its ability to infect cells up to 84 hours at both RT and JT on plastic surface, with a TCID 50 viral titre of 0,67 and 0,25 log10 respectively. At RT, an important reduction in the viral titre, from 4 log10 to 3 log10 TCID50 was observed during the first 24-36 hours. At JT the same decay was observed more rapidly (between 8 and 12 hours), The rate of viral inactivation by D-value was 24.74 at RT and 12,21 hours at JT.

can be influenced by the environmental temperature and that the hot season could reduce the probability of COVID-19 transmission.

INTRODUCTION COrona VIrus Disease 19 (COVID-19) pandemic has been caused by the enveloped Betacoronavirus SARS-CoV-2, transmitted from person to person through respiratory droplets and direct contact, and potentially by indirect contact through fomites (1) .

Several studies have shown that viral spread could be influenced by climatic conditions since enveloped viruses tend to reduce their circulation in summertime due to high temperature and solar radiation (2, 3) . No wonder, the current spread of COVID-19 along the equator and tropics was shown to be significantly less (4), leading to the hypothesis that the increase of temperature will influence the environmental endurance of SARS-CoV-2.

In order to try to predict the effect on the epidemic dynamic of COVID-19 during the summer months, we decided to test SARS-CoV-2 environmental stability in parallel at room temperature (RT, 20°C-25°C) and at average maximum temperature of June (JT) estimated at 28°C in Italy.

The strain BetaCov/Italy/CDG1/2020|EPI ISL 412973|2020-02-20 (5) was used to test SARS-CoV-2 stability on plastic surface (polypropylene). That strain had an initial viral titre of 10 6.8 TCID 50 /ml, a comparable viral load of symptomatic, asymptomatic or minimally symptomatic patients (6) .

The viral preparation was spotted in droplets of 10 µl on 24-well plates and let 30 minutes to dry.

Then, plates were incubated at both RT and JT for 7 days at relative humidity of 35-45% Ethical approval was not need for this study. Viral titre of the daily collections of 0, 24, 48 and 72 hours at RT were determined also by plaque assay in Vero E6 cells. Briefly, 12-well plates were plated with Vero E6 cells (150,000/well in MEM +10% FCS) and inoculated with logarithmic dilutions of each sample. Plates were incubated for 1 hour at 37°C, and 4 ml/well of a medium containing 2% Gum Tragacanth + MEM 2.5% FCS were added. After 5 days at 37°C with 5% CO2, titres were calculated by crystal violet dyeing in plaqueforming units per milliliter (PFU/ml).

All the experimental procedures were conducted under Biosafety Level-3 conditions.

To approximate a normal distribution viral titer of each well was log-transformed. Performing standard deviation with a 95% confidence interval, the results mostly followed a normal distribution J o u r n a l P r e -p r o o f of a set value. Further, the ratio of the standard deviation to the mean was investigated by calculation coefficient of variance.

Analysis of data obtained by TCID50 titration showed that an important reduction in the viral titre, from 4 log 10 to 3 log 10 TCID 50 per milliliter of medium, was observed during the first 24-36 hours at RT (Figure) with a D-value of 24.74 hours.. This trend is confirmed by titration by plaque assay (Appendix).

At JT, the same decay was observed more rapidly (between 8 and 12 hours) indicating that viral infectivity can be influenced by higher temperature with a D-value of 12,21 hours. This decay trend continues until 84 hours showing a remarkable difference between the two temperatures. In both the experimental conditions, the virus is no longer detectable at 96 hours.

The present study confirms that fomite transmission of the emerging SARS-CoV-2 is possible (7) In conclusion, the increase of temperature observed in summer may influence the environmental endurance of the SARS-CoV-2 but do not influence the need of maintaining social distancing measures.

World Health Organization. Modes of transmission of virus causing COVID-19: implications for IPC precaution recommendations. WHO Scientific brief

Association between viral seasonality and meteorological factors

Survival of coronaviruses in water and wastewater

An interactive web-based dashboard to track COVID-19 in real time

Whole genome and phylogenetic analysis of two SARS-CoV-2 strains isolated in Italy in

Viral load dynamics and disease severity in patients infected with SARS-CoV-2 in Zhejiang province, China

Aerosol and surface stability of SARSCoV-2 as compared with SARS-CoV-1

Possible transmission by fomites of respiratory syncytial virus

Virus survival in the environment

Stability of SARS-CoV-2 and other coronaviruses in the environment and on common touch surfaces and the influence of climatic conditions: A review

The authors wish to thank Dr. Paola Stefanelli for providing the virus SARS-CoV-2 BetaCov/Italy/CDG1/2020|EPI ISL 412973|2020-02-20. The authors wish to thank Alessia Caratelli, Ambrogio Carlei, Marina Sbattella and Eugenio Sorrentino for their technical support.

The authors declare no competing interests.

No external funding was received