COVID-19 adversely impacts all human activities. While the Central, State, Municipal/Panchayat authorities are sparing no effort to vanquish the virus, each individual must not lower the bar. They must wear masks; keep 2 metre distance; avoid crowds etc. These are life saving measures. COVID-19 virus is known to get deposited on surfaces. Its survivability on various surfaces is a very important safety related information.
Currently, the reports on the survivability of SARS-CoV-2 on various surfaces are conflicting, with data ranging from 3 to 14 days at room temperature for a single surface type, stainless steel. Researchers at Commonwealth Scientific and Industrial Research Organisation (CSIRO), Australia’s national science agency, carried out an elegant series of studies of important surfaces and have found that this virus can survive under certain conditions for up to 28 days on common surfaces including banknotes, mobile phone screens – and stainless steel.
They studied the survival of the virus on different surfaces at 20, 30and 40 degree Celsius and a humidity level of 50%. Virology journal of 11 October 2020 has published the results from the study. While what is done under laboratory conditions may not be applicable in real life, there is no harm in following a judiciously conservative approach in this matter.
CSIRO researchers carried out the study because they felt that the environmental stability data for SARS-CoV-2 under controlled temperature and humidity conditions for a range of common surfaces are very useful to implement mitigatory measures.
The surfaces studied
The researchers included the surfaces of vinyl sheets, glass, Australian polymer bank notes, de-monetised paper bank notes, cotton cloth, brushed stainless steel; they chose glass due to its prevalence in public areas, including hospital waiting rooms, public transport windows and shopping centres, and high contact surfaces such as mobile phone screens, ATMs and self-serve check-out machines. People come into contact with these surfaces on a daily basis
Surface inoculation and sampling
This study closely mimicked what happens when the virus spreads in the environment. The research involved drying virus in artificial mucus on different surfaces, at concentrations similar to those reported in samples from infected patients and then re-isolating the virus over a month.
The researchers used actual SARS-CoV-2 isolate supplied by thePeter Doherty Institute for Infection and Immunity. They inoculated precisely known amount of virus in artificial mucus onto the centre of each dried sample surface of size 1–1.5 cm2 and carried out the study for various surfaces by sampling at selected time points post inoculation at 20, 30 and 40 degree Celsius and relative humidity 50% using a temperature-humidity adjustable climate chamber
The present study has demonstrated that in controlled conditions, SARS-CoV-2 at a starting viral load and in a fluid matrix equivalent to that typically excreted by infected patients, remains viable for at least 28 days when dried onto non-porous surfaces at 20 °C and 50% relative humidity.
Researchers showed that viral survivability depends on temperature and humidity, an increase in either being detrimental to virus survival.
They claimed that their study provided a reasonable explanation for the outbreaks of COVID-19 surrounding meat processing and cold storage facilities. The result also supports the findings of a recent publication on survival of SARS-CoV-2 on fresh and frozen food.
“This study demonstrated that SARS-CoV-2 is extremely stable on stainless steel surfaces at room temperature (> 28 days at 20 °C/50%RH) however, is less stable at elevated temperatures (7 days at 30 °C and < 48hrs at 40 °C).” The authors asserted
“The persistence of virus on both paper and polymer currency is of particular significance, considering the frequency of circulation and the potential for transfer of viable virus both between individuals and geographic locations” they added.
The researchers observed that while other studies have shown that paper notes harbour more pathogens than polymer notes, the present study demonstrates that SARS-CoV-2 persists on both paper notes and polymer notes to at least 28 days at 20 °C, albeit with a faster rate of inactivation on polymer notes.
Experience in other countries
They noted that prior to SARS-Cov-2 being declared a pandemic, China had commenced decontamination of its paper based currency, suggesting concerns over transmission via paper banknotes existed at the time.
Similarly, the United States and South Korea have also quarantined bank notes as a result of the pandemic. Another notable fact is that after 28 days, researchers recovered infectious SARS-CoV-2 from stainless steel, vinyl and glass, suggesting survivability on paper or polymer banknotes was not very different from the other non-porous surfaces studied.
“ The persistence of SARS-COV-2 on glass and vinyl (both common screen and screen protector materials, suggest that touch-screen devices may provide a potential source of transmission, and should regularly be disinfected especially in multi-user environments.” They advised
The researchers found that COVID-19 virus: survived longer at lower temperatures; tended to survive longer on non-porous or smooth surfaces such as glass, stainless steel and vinyl, compared to porous complex surfaces such as cotton; survived longer on paper banknotes than plastic banknotes.
The authors concluded that the data presented in this study demonstrates that infectious SARS-CoV-2 can be recovered from nonporous surfaces for at least 28 days at ambient temperature and humidity (20 °C and 50% RH). If the temperature is increased while maintaining humidity drastically reduced the survivability of the virus.
“The persistence of SARS-CoV-2 demonstrated in this study is pertinent to the public health and transport sectors. This data should be considered in strategies designed to mitigate the risk of fomite transmission during the current pandemic response.” The researchers suggested. As a matter of fact, adequate care wherever possible is already taken in public health and transport sectors.
An important takeaway
An important takeaway is that it is a safe practice to keep away coins and currency received in any transaction. The former can be washed with soap solution and the letter stored separately for some time. Every time one handles currency and coins, it is desirable to wash hand well with soap.
A COVID-19 patient unknowingly infected a healthy person in a car parts company in Germany as the former handed over a salt shaker to the latter.
Sadly, large sections of our population do not comply with safety precautions. As our tryst with COVID-19 appears to be for a longer duration, safety conscious citizens must call out the defaulters for the safety of every one.