COVID-19: virus lifespan in surfaces is affected by tropical temperatures

Publicação: 10 de November de 2020

Lower temperatures help vírus survival, which according to scientists, resists more in smooth surfaces rather than in porous

The research could help explaning the apparent persistence and dissemination of Sars-CoV-2 in cold environments with high lipidic or protein contamination, as meat processing units

Resarchers at Australia National Science Agency (CSIRO) found out that the vírus causing COVID-19 could survive up to 28 days in common surfaces, such as Money bills, stainless steel and glass, as cell phones for example. According to a study entitled The effect of temperature on persistence of SARS-CoV-2 on common surfaces, published on the Virology Journal lower temperatures tend to favour the virus survival, which according to scientists, is more resistant in smooth surfaces rather than in porous. The research however, was not unanimously accepted by the scientific community.

For this analysis, scientists tested the survival rate of the COVID-19 agent in several surfaes, using a synthetic solution with viral concentration similar to the reported in infected patients’ samples. The study was held in the dark to prevent the effects of UV light, since other researches have shown that direct sunlight can rapidly kill the virus.

To learn more about the subject, the press advisory of the Brazilian Society of Tropical Medicine (BSMT) interviewed Dr. Shane Riddell, leader of the research.

Find the full interview below.

BSTM: Would the discovery that the virus’s survival on surfaces is affected by temperature explain why the pandemic is less severe in the Tropics?

Dr. Shane Riddell: There are many factors that influence survival, humidity and UV light also play an important role. We know that increased humidity also reduces virus survival, and UV light (Sunlight) is very effective at inactivating the virus which would impact aerosol/respiratory droplets as well as surface transmission. I would suspect that the combination of these factors may as least partially explain why the virus is less severe in the tropics.

BSTM: The increase in temperature, maintaining humidity, drastically reduced the virus’s ability to survive to less than 24 hours at 40 degrees. Would that explain why Africa had fewer cases compared to other countries?

Dr. Shane Riddell: It’s possible, however we still don’t yet know the exact role that surface transmission contributes to the spread of SARS-CoV-2.

BSTM: Would the incidence and mortality by COVID-19 be lower in the Tropics due to the survival of the virus on surfaces being minimal?

Dr. Shane Riddell: The epidemiology of the virus is very complex, with transmission known to occur through aerosols, droplets and fomites (or surfaces). Similarly, whilst we know that survival time decreases with increasing temperature, there are other factors that also contribute to this – such as humidity, exposure to UV light and cleaning protocols

BSTM: If so, how to explain the difference between Africa and Latin America, for example?

Dr. Shane Riddell: The risk of contaminated surfaces will also vary dependent on the item and peoples’ behaviours.  Contamination of items that are put directly in the mouth (eg stainless steel cutlery, drinking glasses, drinking straws) obviously present a greater risk if contaminated, than those surfaces which would require hand to mouth transfer (eg grab rails, door handles, ATM machines, phones).  Hygiene behaviours of children are difficult to manage, and could therefore result in outbreaks where children’s environments become contaminated (eg playgrounds).

BSTM: The study raised some criticisms, among them the non-use of fresh mucus as a vehicle. How do you counter?

Dr. Shane Riddell: Our experiments were designed to mimic mucous but were not designed to assess the effects of innate and acquired immune factors in mucous – this was not an immunity study.  We do know that, over time, the amount of viable virus in mucous declines as immunity increases, so that, later in infection, quantitative PCR values will still be high, but viable virus is much less. So our study probably represents a “worst case scenario” in early infection.

BSTM: Some studies indicate that the chance of transmission through inanimate surfaces is very small. Could you talk about this?

Dr. Shane Riddell: While the primary role for transmission of SARS-CoV-2 appears to be via respiratory droplets and aerosols, there is still potential for fomite transmission. The role of surface transmission is still likely to be less common than via aerosol/respiratory droplets however, to fully understand the risk of surface transmission we need to know how long it can persist on high touch surfaces.

BSTM: The study raises the discussion on the primary spread of SARS-CoV-2 (aerosols and respiratory droplets), and fomites. Could you tell us about it?

Dr. Shane Riddell: The study was not designed to compare whether fomite transmission or aerosol spread is more important, we still think that aerosols and respiratory droplets are the primary mode of transmission. In order to determine the risk posed by fomite transmission we need to know how long the virus can persist on a surface and the levels of virus required to result in infection (which we still don’t know), we now have more information in order to evaluate the risk of fomites.

BSTM: Disinfection of surfaces remains highly recommended due to the possibility of the virus surviving for a long time. Regardless of how long the virus stays on each type of surface, does the ability to keep infectious remain high?

Dr. Shane Riddell: The levels of viable virus certainly drop over time, and were extremely low at the 28 day time point (most likely lower than what would be regarded as an infectious dose), our certainly highlights the importance of regularly cleaning and disinfecting high contact surfaces.

BSTM: In your opinion, can the results of the study evidence that the contagion of people is greater due to the fact that they touch contaminated objects where the virus remains longer?

Dr. Shane Riddell: It’s certainly possible however, we think that being in close proximity to an infected person and being exposed to respiratory droplets and aerosols is likely to be a greater risk.

BSTM: Would you like to add something that you consider important?

Dr. Shane Riddell: The main message we want people to take away from this study is that the results reinforce the importance of regular of washing hands, using sanitising hand gels/wipes when out in public.  Avoid touching common surfaces whenever possible and don’t put your fingers in your mouth or rub your eyes.