Confronting COVID-19: An Analysis of Surface Contamination Risks

Officials from the Centers for Disease Control and Prevention have acknowledged that SARS-CoV-2 (also known as COVID-19 or the novel coronavirus) is a new disease and they are still learning how it spreads. This paper was created to outline the recent science behind the transmissibility of the virus that could lead to infection. While not intended specifically for the unique challenges facing banks, it does contain information that all bank employees could find helpful in reducing risk to staff and customers, especially when they utilize an ATM.

The CDC believes that the primary spread of the virus is from person-to-person; specifically, those in close contact (within six feet) and through respiratory droplets expelled by a person through coughing or sneezing. However, the CDC states that it may be possible for a person to become infected by touching a surface or object contaminated with the virus and then touching their mouth, nose, or possibly their eyes.

The goal of this paper is to outline the recent science regarding the risk of infection from contaminated surfaces in an accessible manner. There are many unknowns and many variables around the ability to be infected through an indirect manner, which is why guidance from the CDC and others is always vague. This paper focuses on two different analyses, one from China that appears to show how transmission can occur in an indirect manner and the other from a recent New England Journal of Medicine study on the surface stability of SARS-CoV-2. Using these two papers as baseline, the following can be concluded:

• It is possible to be infected with SARS-CoV-2 through indirect transmission, but it appears to be exceedingly rare, and a whole series of factors must occur to make it happen.
• With proper precautions, you should be able to minimize your risk (to near zero) from indirect transmission when you go outside your house. (This paper does not address the risk from droplet or aerosol-based infection which is why social or physical distancing is still important and people exhibiting symptoms should be avoided.)
• Packages and shipments you receive are likely safe without any additional action.
  • If it is a standard U.S.P.S. mail, UPS or FedEx shipment, the risk is de minimis and should be considered safe.
  • If it is a same-day delivery, it is still likely safe, and if left to sit for 12-24 hours at room temperature the risks become de minimis as well.
  • If it is a takeout or near real-time food delivery, the likelihood of significant contamination being on the package is still very low, especially if prepared by asymptomatic personnel, but out of an abundance of extreme caution wiping down the high-touch parts of the packaging with an approved cleaner and then washing your hands, likely reduces the risks to near zero.
• Items brought home such as groceries and office supplies are likely safe. There is always the potential that an infected person placed a significant amount of contaminant on an item that they then replaced and you then picked up the same day and purchased, but it would be extremely unlikely and unlucky. If you are concerned you can wipe down your groceries, but for non-perishable items, letting them sit at room temperature for 12-24 hours or longer brings the risk to near zero. For items that go in the refrigerator, if you are concerned, you can wipe them down as the virus in most scenarios remains viable longer at colder temperatures ¹.

Q: Can I get coronavirus from a contaminated surface?

The CDC believes that fomite (shared surface transmission e.g. door handles, elevator buttons, etc.) transmission is possible based upon the Wenzhou shopping mall cluster analysis.² A grouping of SARSCoV-2 cases in a Wenzhou, China shopping mall allowed Chinese epidemiologists to determine how people became infected in the mall by closely analyzing where SARS-CoV-2 positive people went and with whom they interacted. The analysis shows that “the virus spread by indirect transmission.”2 It is very important to note that the transmissions described appears to be from contemporaneous, or within the same day, of contact with shared surfaces. The shared surface transmission vectors (fomites) were likely bathroom fixtures, doorknobs or elevator buttons — areas and fixtures likely cleaned nightly rather than repeatedly throughout the day.

In this study, an index patient appeared to infect six of her coworkers who all worked in the same room and were diagnosed prior to any other diagnoses in the mall. This initial set of infections could have been through droplet/aerosol transmission due to close contact working conditions and included both men and women. After the initial seven diagnoses, an additional 16 people appear to have been infected through fomites. “All…were female, including a restroom cleaner, so common restroom use could have been the infection source.”² These transmission vectors were determined through very aggressive contact tracing to isolate the potential cause of the illness.

What this means:

While it is possible to be infected by the virus from a contaminated surface in a public space, it is very challenging. Conservatively, foot traffic in a mall the size of that in Wenzhou (at least eight stories of retail space), in a city of 8 million is at least 10,000 shoppers a day and likely much higher. The report shows that the 16 customers presumably infected at the mall during the days tracked visited on different days and only four visited on the same day. So even though seven infectious people were working in the mall and visiting other shops, only one, or at most four, people out of the tens of thousands a day who visited became infected. Essentially this type of transmission is extremely rare. Additionally, all who were infected were female, including a female restroom cleaner, so the restroom fixtures appear to be likely contamination points versus other surfaces within the mall. It is important to note that the originally infected seven mall employees worked and moved throughout the mall over several days and infected a nearly negligible number of other people who came into the mall. The transmission method cannot be known with certainty, but we can say that being in the same relatively large open space of a mall with infected individuals did not lead to large-scale infections. This is very good news and seems to indicate that there is limited risk in going out in public, either outside or in open floorplan buildings like supermarkets, to being infected via aerosol or droplet transmission especially if social or physical distancing is maintained.

What this means to you:

While it is possible to be infected if you go out in public, it is exceedingly rare to be infected via indirect transmission and with proper precautions you can reduce the risk significantly. First, avoid anyone who appears symptomatic as people who are coughing or sneezing are shedding and projecting the virus as droplets (and potentially aerosols) into the environment where they can land in the mouths or noses of people who are nearby and possibly be inhaled into the respiratory tract. This is the primary reason for social or physical distancing. An additional risk mitigation technique is to avoid smaller indoor areas that contain multiple people — follow the CDC guidance of limiting gatherings to 10 people.

After airborne/droplet transmission, the highest risk appears to be from high-touch surfaces such as bathroom fixtures, door handles, shopping cart handles, etc. Handle those types of interactions carefully. If you can, wipe them down before use. If you cannot, recognize after you touch them that your hands, even though very unlikely, may be contaminated. This is okay as long as you don’t touch your face and provide the virus a path into your body. Continue your shopping trip, making sure not to touch your face, but prior to getting back in your car or touching a surface you own, sanitize your hands and/or remove whatever gloves you have on. If you are carrying shopping bags, load them first, preferably not through the driver’s door. Then take off your gloves or sanitize your hands (and car key if used to open the door) prior to opening your driver’s door. This ensures your hands are clean and you won’t transfer virus to your door handle or more importantly your steering wheel.

Q: How likely is it that I’ll get coronavirus from a contaminated surface?

There are a lot of news articles based upon a limited number of studies that discuss with alarm how the virus can be found on surfaces one day, four days or even weeks later. It is useful to think about how you get sick from a contaminated surface. You need three things:

1. You need to transfer the virus from a contaminated surface onto yourself, most likely by touching something with your hand, and then;
2. You need to transfer the virus from your hand into your body. For SARS-CoV-2 it is believed to enter through your eyes, nose or mouth, and then;
3. You need a sufficient amount of the virus to enter your body to actually make you sick. While there are a limited number of studies on infectious dose-rates that use measures such as a 50% tissue culture infectious dose (TCID₅₀) or Plaque Forming Units to measure the amount of virus to make you sick, it is likely that it will require a significant number of virions (potentially thousands) to make you sick with the virus.

For each of those steps, the amount of virus being transferred gets decreased as no transfer mechanism is 100%, so, if you work backwards to step one, someone sick needs to leave a substantial amount of viable, meaning it is infectious and can make you sick, virus on a surface. Those two items are key and should drive how you consider risk mitigation techniques and what it means when an article says the virus can be found on the surface three days later. Is the virus viable or does just the RNA remain of a “dead” virus? Is it in substantial quantity or only trace amounts? On March 20, Carolyn Machamer, a professor of cell biology at Johns Hopkins School of Medicine who has studied the basic biology of coronaviruses for years said,

“What’s getting a lot of press and is presented out of context is that the virus can last on plastic for 72 hours—which sounds really scary. But what’s more important is the amount of the virus that remains. It’s less than 0.1% of the starting virus material. Infection is theoretically possible but unlikely at the levels remaining after a few days.”

We know the virus starts to degrade and die once it leaves the cozy confines of its host. A recent study published in the New England Journal of Medicine³ attempted to measure the aerosol and surface stability of SARS-CoV-2. They created a viral solution of 105 TCID₅₀ per mL which is the same concentration levels as those “observed in samples from human upper and lower respiratory tract” (Appendix)³, deposited them on different surfaces, and then measured over time how much the virus degraded.

Fundamentally, the concentration they put on the surfaces likely mimics the concentration that you would see if someone sneezed or coughed droplets onto a surface or potentially touched their nose or mouth and touched a surface. There are no absolutes, but it is a reasonable assumption that concentration levels would be similar. They then measured how long the virus would remain viable on those surfaces. Here’s what they found:

Figure 1. Predicted Decay of Virus Titer3

One thing to note is that the vertical axis is on a log scale, meaning it measures by a factor of 10 so 10⁰ is equal to 1, 10¹ is equal to 10, 10² is equal to 100 and so on.

Looking at these charts you can see where the headlines come from. The virus is viable on plastic for about 72 hours and on cardboard for 24 hours but remember that viability is only half of the equation. You must have the virus present in significant enough quantity to get you sick. Looking at the concentrations of viable virus remaining over time offers a much more nuanced look.

Table 1 (below) shows the degradation of viable virus over time for steel, cardboard and plastic using the median half-life calculated in the Appendix and assuming a starting concentration of 100,000 or 10⁵ TCID₅₀ per mL which is a similar concentration to that observed in the respiratory tract⁴.

Table 1. Degradation estimates of viral viability over time using the median half-life estimates at 21 to 23 C and 40% relative humidity.

(This table is updated from the April 5, 2020 publication where the Plastic and Cardboard columns were mis-labeled and there was a rounding error in the calculation.)

These are listed as concentrations per milliliter. Clearly the total dose or amount of virus can increase if more concentrate is present, so if you had 2mL of virus at a concentration of 100,000 TCID50 that would equate to 200,000 TCID50 of total virus. It’s helpful to remember what a mL of liquid is. One way to visualize it is to think of a child’s dosing syringe or those small plastic cups used for cough medicine.

A mL of liquid is a visible amount of liquid and the point is that unless the initial concentration of virus on the surface is very high, and the concentration amounts that people leave behind in the real world will vary significantly, it is hard to transfer a high concentration to you through surface contamination.

The challenge is that no one knows what a true infectious dose is and the actual amount varies by person, their health, how the virus gets introduced into the body, where it lands in the respiratory system, and many other factors.

The important thing to remember is that the virus does degrade over time and at a substantial rate, so the one thing that can be said unequivocally is that the risk from surface contamination goes down over time at room temperatures.

Going back to the previously described three steps required to get sick from a contaminated surface:

1. You need to transfer the virus from a contaminated surface onto yourself, most likely by touching something with your hand.
   1. We know that the concentrations of the virus in the human respiratory tract are around 10⁵ TCID₅₀ per mL, which means any surface contaminant is likely to be at that level or lower.
   2. We also know the virus begins to degrade and decrease in quantity as soon as it leaves the human body, so the amount available on a surface depends on how long it has sat there since being deposited.
2. You need to transfer the virus from your hand into your body. For SARS-CoV-2 it is believed to enter through your eyes, nose or mouth.
   1. There will be some loss of the virus in the transfer from the surface to your hand to your body further decreasing the amount of virus you introduce to yourself.
3. You need a sufficient amount of the virus to enter your body to actually make you sick.
   1. This is where the most variability lies. There does not appear to be good data on what the actual infectious dose is for a person.
   2. As we know people can get sick via fomites, but it appears to be very rare and is likely a combination of a perfect storm of a large amount being deposited, someone coming into contact with it after a relatively short period of time, and then creating a pathway into their body.

Case Study: Using a Bank Drive Through ATM

Looking at the previous analysis, what are the concerns in completing a transaction at an ATM. An ATM touchpad could be considered a high-touch surface, and so appropriate precautions should be taken. Even though the likelihood of any level of significant contaminant being present on the buttons is low, after use simply use a hand sanitizer and the risks become negligible.

As far as the currency removed, there is a lack of testing data on viral viability on United States currency, so we’ll use the viability data for cardboard as the closest neighbor. Based on how currency is loaded into an ATM using cassettes that fundamentally limit the physical interaction with the technician, there’s limited chances for cross contamination. Even if a bill were somehow contaminated in a significant manner, if the currency was loaded 24 hours prior, an estimated 90% of the virus would have already degraded and the risks become very low. If after you use the ATM, place the currency in your wallet, don’t touch your face and immediately use a 60% or higher alcohol-based hand sanitizer, your risks are negligible.

Conclusion

Fundamentally, it appears that it is very difficult to became infected with SARS-CoV-2 via contaminated surface transmission. Looking at the Wenzhou shopping mall cluster case — where it appears only 16 other people became sick out of the tens of thousands of people who potentially had contact over an extended timeframe — shows how challenging indirect infectivity can be. With appropriate precautions, it is likely that the risk from fomites can be de minimis during shopping excursions out of the house and the focus should be ensuring appropriate social or physical distancing is maintained to minimize the risk from droplet/aerosol-based transmission.

This document is provided as an informational resource only and should not be considered medical advice. Use of the recommendations and insight are a matter of personal choice and are not official ABA or governmental position or policy. The views in the paper are the author’s own based on professional experience and a review of recent research.

About Paul Benda

Paul Benda holds a Masters degree in Mechanical Engineering from Purdue University. He led the Pentagon’s response to the suspected Anthrax attacks in 2001 and was a government Program Manager at the Defense Advanced Research Projects Agency where he focused on developing technologies and systems to defend against chemical and biological attacks. Later he was the Senior Executive in charge of deploying and operating an advanced chemical and biological protection system at the Pentagon and oversaw the technological defenses, sampling programs, hazardous materials teams, onsite laboratory, and testing programs. During his tenure, the Pentagon conducted the most comprehensive set of tests regarding simulated biological attacks and decontamination procedures in modern history. He currently works as Senior Vice President of Risk and Cybersecurity Policy at the American Bankers Association (ABA). The views in this paper are his own.

Endnotes

1 Casanova, L. M.; Jeon, S.; Rutala, W. A.; Weber, D. J.; Sobsey, M. D., Effects of air temperature and relative humidity on coronavirus survival on surfaces. Applied and environmental microbiology 2010, 76 (9), 2712-2717. https://misuse.ncbi.nlm.nih.gov/error/abuse.shtml

2 Cai J, Sun W, Huang J, Gamber M, Wu J, He G. Indirect virus transmission in cluster of COVID-19 cases, Wenzhou, China, 2020. Emerg Infect Dis. 2020 Jun [date cited]. https://wwwnc.cdc.gov/eid/article/26/6/20-0412_article.htm

3 van Doremalen N, Bushmaker T, Morris DH, et al. Aerosol and surface stability of SARS-CoV-2 as compared with SARS-CoV-1. N Engl J Med. DOI: 10.1056/NEJMc2004973, https://www.nejm.org/doi/full/10.1056/NEJMc2004973

4 Zou, L., Ruan, F., Huang, M., Liang, L., Huang, H., Hong, Z., Yu, J., Kang, M., Song, Y., Xia, J., Guo, Q., Song, T., He, J., Yen, H.-L., Peiris, M., Wu, J., 2020. SARS-CoV-2 Viral Load in Upper Respiratory Specimens of Infected Patients. N. Engl. J. Med. In press.