Pieces of the SARS-CoV-2 virus are detectable after breathing, using the toilet, and touching surfaces, but this study did not recover any infectious virus particles nor provide evidence of human-to-human spread of COVID-19 through small airborne particles or surfaces.
- High rate of environmental contamination - the vast majority of samples from COVID-19 patient rooms, personal objects, and the air showed parts of the virus’ genetic code
- The recovered virus particles did not infect cells in the lab so it is unknown if any of the virus was still living
Why is this important?
In order to design effective policies and procedures to prevent the spread of COVID-19, we need to know if it’s spread by droplets versus airborne transmission. The difference is that droplets are generally large and fall relatively quickly on the ground and objects nearby, and aerosolized particles (airborne transmission) happens with much smaller droplets that can hang in the air for a much longer time period.
If COVID-19 is spread by airborne transmission, much stricter restrictions need to be placed in order to protect the general public. This difference is important for indoors activities, especially in shared spaces with heavy breathing, like concerts, gyms or choirs. Surface transmission is also important to understand for policy making. For example, based on current research, the CDC does not believe that contaminated objects are a main source of infectious spread. Any evidence either supporting or refuting this would be very valuable to have.
During the course of this study the researchers at the University of Nebraska gathered samples from a small number of patients infected with COVID-19. Samples were taken from common objects (remote controls, phones, personal items, etc), surfaces (bathrooms, window ledge, air gratings), and air (both inside the patient’s room, as well as the hallway outside). Between 50-100% of each sample type showed viral genetic materials, meaning the presence of the virus or parts of the virus. Samples from patients’ rooms who had a higher fever did not show a higher level of virus. Air samples from patients who required hospital care (more severe symptoms) did not show a higher level of virus than air samples from the patients who had mild or no symptoms. The researchers were not able to use the virus samples obtained from objects or the air to infect cells in a laboratory setting.
The biggest strength of this study was that they tried to culture all of their samples to see if the virus could infect cells in a laboratory setting. The University of Nebraska’s Biocontainment and Quarantine units have the resources to perform this kind of study which most places cannot easily do.
It’s not clear from the paper if they had successfully cultured SARS-CoV-2 from a hallway air sample. The text suggests that they did not and Figure 2 suggests that they did. The difference between these two interpretations is huge, because if the hallway air sample was infectious, that suggests airborne transmission. They were unable to use any of the other samples to infect cells.
This paper was missing some important positive and negative controls. The infection of cells in a lab setting did not have a positive control - for example, asking a patient to provide a droplet sample and culturing that using the same methods. Because of how they did it, we have no idea if the samples were not infectious, or if they were not infectious because of how they were handled. The testing for the presence of genetic material did not have a negative control. This is important to show that there was no contamination or other errors.
What did the study do?
Collected surface and air samples from rooms and personal items of COVID-19+ patients
Researchers sampled surfaces of common personal items like cell phones, common room areas like tabletops, and toilets. They also sampled hard to reach areas like ventilation grates and underneath beds. They also sampled air from rooms and hallways of COVID-19+ patients and also from devices worn by COVID19- facility workers maintaining social distance.
Reasonable sampling methods
Researchers sampled a wide range of air spaces and surfaces.
Not real world scenarios
All of these patients were symptomatic, knew their diagnosis, and were living in a hospital. This might not reflect real world scenarios, like asymptomatic carriers, or presymptomatic patients in early stages. Real world cases might be more or less infectious than these patients.
Lack of details and consistency about the samples
The samples were not consistent and uniform. For example during the sampling of the air inside the patients rooms, some patients removed their masks, and others did not feel comfortable and did not remove their masks, meaning we don’t know how wearing a mask might affect air contamination.
There was a delay between diagnosis and sampling
All of the samples were collected at least 5 days after diagnosis and most after 10 days. If people are most infectious early in the disease, this study would miss that.
Tested for genetic material in their samples
Researchers first used a test called polymerase chain reaction (PCR) to look for the virus. This test works by looking for parts of the virus' genetic material (RNA). PCR only tells us if the virus’ genetic code is present, not if it is infectious.
Lack of negative controls
Negative controls are very important. It can help scientists rule out contaminations or other complications with their tests or samples. The researchers could have shown that their tests were sound by examining samples from patients who did not have COVID-19, but they did not do this.
Tried to infect cells with the samples they collected
Growing virus in the lab requires infecting cells with the virus. These kinds of experiments are challenging to do correctly. The researchers were not able to grow any virus samples.
The culture data is inconclusive
One way to test if your lab experiment is correctly growing the virus is to use a positive control which is a sample that you know contains living virus. For example, researchers can take a mucus sample from the lungs of a COVID-19 patient. Assuming the experiment is working correctly, the virus should infect cells in the lab and grow.
Because the researchers did not test their equipment and methodology by using a positive control, we do not know if the samples were actually not infectious or if they simply did not grow because the experiment was done incorrectly.
Found virus genetic material on surfaces and in places that suggest airborne transportation, but does not show airborne infectivity
The researchers found genetic material from the virus in places that would not be reached by large droplets, suggesting that the virus particles can be spread via airborne transmission. They also found the virus on most of the surfaces that the patients had interacted with. But, those samples were unable to infect cells in a laboratory setting. As noted above, it's possible the virus was no longer functioning or "living", or this simply could be an issue with the experiment.
Environmental contamination with virus particles is common, suggesting airborne transmission
Limited support for conclusion
Whether COVID-19 can be spread through the airborne route (tiny droplets that hang in the air for a long time) or from touching contaminated surfaces is still unknown. While they clearly found pieces of the virus in the air and on surfaces, none of their samples were able to infect cells in a laboratory setting, so we cannot conclude that surfaces containing virus particles are a major source of infection.
We hope that follow-up studies can help clarify this important issue.