Transmission of COVID-19 on Surfaces

As the pandemic continues, many people are more aware of the importance of maintaining clean surfaces within their homes, businesses, and shared spaces. Determining which surfaces might hold viral material longer than others is vital. Several studies have been conducted, none perfect, but could potentially shed better light on this important concern.

How long does COVID-19 remain on surfaces?

The main study cited in making recommendations regarding COVID-19 transmission off of surfaces and fomites (objects that could carry infection) comes from a study published in the New England journal of medicine comparing the stability of SARS-CoV-2 and SARS-CoV-1, in aerosols and on surfaces. Experimental conditions included aerosols, plastic, stainless steel, copper, and cardboard. Results were based on the time it took for the viral load to reach a certain level after inoculation on the surface, averaged from multiple replicates of each condition. Based on this method, SARS-CoV-2 was found to be “more stable on plastic and stainless steel than copper or cardboard”(1). So what does this mean in terms of time? The study found that similar levels of viable viruses were detected on plastic after 72 hours and on stainless steel after 48 hours. No viable virus was able to be measured on either copper after 4 hours or cardboard after 24 hours. This means the virus was able to survive on plastic the longest, followed by steel, and it was able to survive longer on cardboard than copper but was ultimately non-viable after 24 hours. Further qualification of the results includes the fact that while the virus was still detected on stainless steel and plastic after the longest periods, there was an exponential decay in viral load over that period, and the data of the cardboard experiments had more variability, leading to a larger standard error. This matters in two different ways.

- One is while the virus may be detectable on plastic and steel, the amount of the virus on the surface at the time of contact would matter when it comes to the potential of infecting individuals.

- Second, in regards to cardboard, higher variability in the results could indicate that there was some unknown factor affecting the experiment.

Therefore, results are not as accurate compared to the data from the other surfaces. Based on the results of the study, the authors state that the most likely reasons for the “epidemiological characteristics” of SARS-CoV-2 (how readily it has spread through the population) are due to “high viral loads in the upper respiratory tract, and the potential for persons infected with SARS-CoV-2 to shed and transmit the virus while asymptomatic” (1). In summary, while the virus can survive on surfaces for several hours, it is unlikely that the surface will remain a viable infection source due to exponential viral decay that will render the viral load too small to effectively pass on the virus in a matter of hours.

How does COVID-19 spread, and possible infection from surfaces?

Similar to previous coronavirus diseases, the main route of transmission for COVID-19 is person-person via respiratory droplets. This has led to lots of focus in the media and online about the importance of wearing masks and following social distancing guidelines. However, there has also been discussion and fear surrounding other modes of transmission, such as contamination of inanimate surfaces and even animal to human transmission (2). The chain of transmission from a surface starts with an infected person touching a surface or object, depositing a certain amount of virus onto the object’s surface, where the virus then survives until an uninfected person touches the object. That person then self-inoculates themselves or others by touching skin or a mucous membrane such as the nose, eyes, or mouth (3). While this is a plausible route of transmission, there are certainly more barriers to infecting others than directly breathing in respiratory droplets, such as the initial viral load transferred to the surface, how well the virus can survive on that surface, ambient temperature, humidity, exposure to sunlight (4), and host behavior (how often people wash or disinfect their hands and touch their faces) (5). While research is still ongoing, several characteristics of the virus have already been discovered from studied cases. There has been no detection of COVID-19 in drinking water sources. There has been no evidence of anyone contracting the virus from handling food containers/packages, being exposed to water in a swimming pool/hot tub, or through mosquito or tick bites (2). While there have been cases of pets having asymptomatic infection after being in close contact with people positive for COVID-19, “experts don’t consider animals to be a significant way that coronavirus spreads” (2). While research into the transmission of coronavirus will continue, it is important to recognize the modes of transmission that will have the greatest impact and to focus attention on slowing the transmission of the virus efficiently.

One way to prevent transmission of COVID-19 contamination while outside of the home

When discussing the transmission of COVID-19, there is one crucial difference between infection via respiratory droplets and surface transmission that makes surface transmission preventable. While respiratory droplets require masks and social distancing to prevent transmission, the surface transmission would require inoculation through some kind of direct contact with an uninfected person, either through the skin or mucous membranes. In a study conducted by Kwok et al., it was found that in a period of 240 minutes, a group of 26 students touched their faces a combined 2,346 times, with 44% of those gestures coming in contact with mucous membranes (5). This study highlights how touching the face is a part of our behavior that can sometimes be unconscious. With all of the major adjustments, people have been making in response to COVID-19, being aware not to touch your face could be a minor change that would have a big impact. This could also be a secondary benefit of wearing a mask; while the main protection that masks offer is from respiratory droplets, having the mouth and nose covered while in public and not disturbing the mask until hands have been sanitized will cut down on face touching and direct contact with two common mucous membrane sites that could be routed for self inoculation.

Current recommendations when dealing with contaminated surfaces and objects inside the home
While the focus of avoiding viral contamination is important, with the prevalence of asymptomatic viral shedding, it is reasonable to assume that objects and surfaces that we interact within our daily lives may be contaminated with COVID-19. Therefore, we must know how to properly disinfect and clean these objects and surfaces regularly. Based on studies of previous coronaviruses, (6), (7), (8), and a study from Singapore in the early stages of the COVID-19 outbreak, while the virus readily spreads to surfaces, it is sufficiently inactivated by a variety of available cleaning agents. The virus is even inactivated by sunlight, given a long enough exposure time. (4) Current CDC recommendations include disinfectants registered through the EPA, alcohol-based solutions of 70% or more or bleach solutions of 5-6% as sufficient to deactivate the virus in as little as 1 minute of exposure time. (9) UV radiation, which is a component of natural sunlight, has also been found to be effective in deactivating COVID-19 but requires at least 15 minutes of exposure time. The exposure time can be shortened if higher frequency UV light is present, typically generated artificially (4). As mentioned before, infection from animals is thought to be rare. However, experts recommend that animals be treated like family members and maintain social distancing of 6 feet away from other animals and people outside of the household.

While research is ongoing, it would appear that infection via surface transfer is most likely in settings of heavy contamination, namely in healthcare settings and homes of infected individuals (4); therefore, extra recommendations are indicated if infected individuals are cohabitating with uninfected individuals. Isolate the infected individual into their room; they should eat separately from other members of the house or have family members bring them food in their room. When doing dishes, wear gloves, and wash them with hot water. They should have a dedicated trash can/liner for their use. It is reasonable to launder items of infected and uninfected individuals together; however, when handling contaminated clothes it is important to wear gloves and not shake clothing before placing it into the washer, to minimize viral particles becoming airborne. Disinfect laundry hampers after emptying (9).

In summary, maintaining a clean environment is key to preventing the spread of COVID-19, and while surfaces may be easily contaminated, they can be easily cleaned to mitigate the chances of infection.