Sunday, June 28, 2020

EID Journal: Prolonged Infectivity of SARS-CoV-2 in Fomites


Fomites are any surface or object that can become contaminated with viral, fungal, or bacterial pathogens and that can then later contaminate - and possibly infect - anyone who touches or handles them.  

Important, because research (see AJIC Face touching: A frequent habit that has implications for hand hygiene) has shown that when in public, we touch our face/mouth/nose frequently; often 20+ times an hour.

Common fomites include the turnstile at the subway, the touch screen on your bank’s ATM, the door handle to your office's microwave, the change the cashier gives you at the checkout lane, and the handle of your shopping cart . . . the list is endless.

In 2014's ICAAC Video: How Quickly A Virus Can Spread In A Building, we looked at an experiment on fomite transmission, which they described as:
Using tracer viruses, researchers found that contamination of just a single doorknob or table top results in the spread of viruses throughout office buildings, hotels, and health care facilities. Within 2 to 4 hours, the virus could be detected on 40 to 60 percent of workers and visitors in the facilities and commonly touched objects. Simple use of common disinfectant wipes reduced virus spread by 80 to 99 percent. 
We revisited this topic again in 2018, in  Study: Simulated Influenza A Transmission In An Office Environment, that found:
Influenza A transmission in a graduate student office is simulated via long-range airborne, fomite, and close contact routes based on realistic data of human behaviours. The long-range airborne, fomite and close contact routes contribute to 54.3%, 4.2% and 44.5% of influenza A infections, respectively. 
For the fomite route, 59.8%, 38.1% and 2.1% of viruses are transmitted to the hands of students from private surfaces around the infected students, the students themselves and other susceptible students, respectively. The private surfaces of infected students are highly contaminated. 
Past studies have focused primarily on influenza, but in 2015's IDWeek: Persistence Of MERS-CoV On Hospital Environmental Surfaces, we looked at the widespread MERS coronavirus contamination found in South Korean hospitals during their multi-hospital epidemic 5 years ago.

A more recent study (see EID Journal: Aerosol and Surface Distribution of SARS-CoV-2 in Hospital Wards, Wuhan, China) found extensive surface contamination in and around a ward treating COVID-19 cases, although the viability of the viruses was not tested. 

Despite all of this research, how much of COVID-19's transmission actually comes from contact with contaminated fomites remains unknown.  The CDC's COVID-19 Transmission webpage states:

The virus is thought to spread mainly from person-to-person. 
  • Between people who are in close contact with one another (within about 6 feet).
  • Through respiratory droplets produced when an infected person coughs, sneezes, or talks.
  • These droplets can land in the mouths or noses of people who are nearby or possibly be inhaled into the lungs.
  • COVID-19 may be spread by people who are not showing symptoms.
But they also grant that: 

The virus may be spread in other ways

It may be possible that a person can get COVID-19 by touching a surface or object that has the virus on it and then touching their own mouth, nose, or possibly their eyes. This is not thought to be the main way the virus spreads, but we are still learning more about how this virus spreads.

One of the big unknowns is how long the SARS-CoV-2 virus remains viable (and infectious) on different types of surfaces, and under different environmental conditions (temperature, humidity, UV rays, etc.). 

Six weeks ago, in DHS: Decay Rate Calculator For SARS-CoV-2 we looked at simple, but limited tool to calculate the half-life of the virus on non-porous materials under various temperatures and humidities.

All of which brings us to a new study, published this week in the EID Journal, that looks at the persistence of SARS-COV-2 on surfaces - and finds that those that are mixed with proteins (such as found in respiratory fluids) are particularly long lived.  

First some excerpts from the research letter, then I'll return with a postscript:
Research Letter

Boris Pastorino, Franck Touret, Magali Gilles, Xavier de Lamballerie, and Rémi N. Charrel 
Author affiliations: Unité des Virus Émergents, Marseille, France.
We spotted severe acute respiratory syndrome coronavirus 2 on polystyrene plastic, aluminum, and glass for 96 hours with and without bovine serum albumin (3 g/L). We observed a steady infectivity (<1 log10 drop) on plastic, a 3.5 log10 decrease on glass, and a 6 log10 drop on aluminum. The presence of proteins noticeably prolonged infectivity.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has spread worldwide, demonstrating a great potential for direct and indirect transmission between humans. Coronaviruses can keep their infectivity in fomites and thus can remain infectious on dry surfaces for hours (1,2). However, limited data are available for SARS-CoV-2 (1). Specifically, there are no data about the role of interfering substances such as proteins on SARS-CoV-2 infectivity in the environment.
We evaluated the stability and infectivity of SARS-CoV-2 deposited on polystyrene plastic, aluminum, and glass for 96 hours at 45%–55% relative humidity (recommended for indoor living spaces by the American Society of Heating, Refrigeration and Air Conditioning Engineers) and 19°C –21°C temperature range using a 106 50% tissue culture infectivity dose (TCID50)/mL inoculum.


Our data showed that SARS-CoV-2 infectivity was remarkably preserved in the presence of proteins, regardless of the type of surface. A final concentration of 11.4 g/L of proteins, as used in our study, closely mimics that of respiratory fluids, which possess protein concentrations of a similar order of magnitude. However, the respiratory body fluids are complex media including not only proteins, but also enzymes and mucins (present in mucus) that may have a negative effect on virus infectivity. Regarding viral load measurement, the reason for avoiding the use of molecular techniques such as reverse transcription PCR is that despite that they allow quantification of RNA copies and determination of RNA decay, they cannot measure residual infectivity on various surfaces.

The protective effect of proteins had already been described for pandemic SARS-CoV or suggested for influenza A(H1N1) virus, but with less notable effects (4,6). As illustrated in other virus models (7), interfering substances such as proteins influenced the resistance of SARS-CoV-2 to drying and thus its persistence in the environment.

In conclusion, we showed that a moderate protein concentration in droplets markedly increased the infectivity of SARS-CoV-2, suggesting that a protein-rich medium like airway secretions could protect the virus when it is expelled and may enhance its persistence and transmission by contaminated fomites.
Accordingly, it is plausible that fomites infected with SARS-CoV-2 play a key role in the indirect transmission of coronavirus disease (COVID-19). This finding supports surface cleaning as a necessary action that should be enforced and repeated becuase it may play a key role in halting SARS-CoV-2 transmission and mitigating the COVID-19 pandemic.

Dr. Pastorino is research engineer with a PhD in virology. His primary research interests are biosafety aspects of Biosafety Level 3 viruses in the context of preparedness and response against epidemics.

Although we tend to think of an infected person touching a surface in order to contaminate it, research has shown that coughing, sneezing, and even talking can aerosolize the virus, or project large virus-laden droplets, both types which will eventually settle out of the air and onto surfaces. 

There are also mechanical ways to aerosolize, and potentially spread, the virus.  Earlier this month, in EID Journal: More Toilet Plume Research In A Time Of COVID-19 and again in Another Toilet Plume Study To Ponder, we looked at the potential for flush toilets to spread the virus. 

While exact role that contaminated fomites play in the COVID-19 pandemic remains unquantified, the available evidence suggests it plays a non-trivial role, making the CDC's guidance on fomites (see Extended Guidance for Cleaning and Disinfecting (Homes, Schools, Businesses, etc.) and hand hygienenothing to sneeze at.