COVID-19 Disinfectants: Does Disinfecting Streets Work Against The SARS-CoV-2 Coronavirus?

COVID-19 Disinfectants: As the COVID-19 escalates, one would have probably have seen photos and video of workers in protective gear using high-pressure sprays to sanitize city streets. Countries like Spain has even taken the radical step of spraying bleach on beaches. https://www.bbc.com/news/world-europe-52471208 You may have asked yourself if this really makes much difference to the risk of SARS-CoV-2 coronavirus transmission. If not, why are authorities spending time, resources and money doing it?


 
Armed with knowledge of the conditions required for disinfectants to work, we suspect these activities are as much about authorities being seen to do something as about actually stopping the spread of COVID-19.
 
Typically, the likely effectiveness of spraying streets and other public places depends on how the virus spreads, how the disinfectants work and what conditions these are used in.
 
Fortunately based on studies, we now know the virus is spread mainly in two ways.
 
Firstly it is through airborne droplets and aerosols that originate from infected individuals. https://jamanetwork.com/journals/jama/article-abstract/2763852 The droplets are expelled into the air through a cough or sneeze and can infect another person who encounters them at close range. Droplets are larger and do not remain in the air for very long, quickly settling to the ground or another surface.
 
Basically aerosols are smaller and remain suspended for longer up to three hours. https://www.nejm.org/doi/full/10.1056/NEJMc2004973 Aerosols will rapidly dry out and disperse over time. This makes it less likely a person will be exposed to enough viral particles known as the infectious dose to be infected. https://www.cidrap.umn.edu/news-perspective/2020/03/commentary-COVID-19-transmission-messages-should-hinge-science and https://www.newscientist.com/article/2238819-does-a-high-viral-load-or-infectious-dose-make-COVID-19-worse/
 
The other  way the disease is spread is via contamination of surfaces. When droplets settle, the virus can persist for varying periods, depending on the nature of the surface. For example, one study found the virus survives for up to 72 hours on plastic and stainless steel, 8 hours on copper and 4 hours on porous surfaces such as cardboard. https://www.nejm.org/doi/full/10.1056/NEJMc2004973

However this experiment was conducted under laboratory conditions indoors. So far, no information is available on how long the virus can survive outdoors. It's also unknown how likely it is for you to become infected when you're walking the city streets.
 
It is important understand the process of disinfection. According to news reports, https://www.businessinsider.com.au/coronavirus-sanitation-disinfection-around-the-world-in-photos-2020-3?r=US&IR=T most authorities are using a diluted bleach solution to disinfect city areas. Research suggests the COVID-19 virus is susceptible to bleach, but it requires a contact time of about one minute to be effective. https://www.sciencedirect.com/science/article/pii/S0924857920300674#bib0045
 
It has been observed that even if the disinfectant reaches every outdoor surface likely to be touched by people, including areas shielded from the spray, there is still a problem with using bleach in the typical conditions encountered outdoors. Sunlight and the build-up of oxygen can deactivate the chlorine, the active ingredient in bleach. This means the disinfectant would probably become ineffective before the virus is killed. https://www.cdc.gov/vhf/ebola/clinicians/non-us-healthcare-settings/chlorine-use.html
 
In order for the coronavirus to infect a person, it needs to enter the body. This can occur when your hands have become contaminated by touching a surface and you put your hands to your face, near your nose or mouth. But when was the last time you touched the ground and then touched your face without washing your hands?
 
The typical average person is rarely going to come into direct contact with city streets and footpaths with their hands. That's another reason spraying these surfaces with disinfectant is unlikely to be an effective control measure.
 
It has also been observed that commonly touched surfaces such as handrails and road-crossing buttons are more likely sources of infection but would have to be cleaned before being sanitized with bleach. This is because organic matter builds up on frequently touched surfaces, including the natural oils on human skin. Even if cleaning were undertaken prior to sanitizing, this process would need to be continuous as the next time an infected person touches the surface it can be recontaminated.
 
It has been proven that spraying disinfectant into the air will have the effect of reducing the amount of virus that is suspended as aerosols. However, this will have a very limited effect as the disinfectant will rapidly disperse. Aerosols will be reintroduced the next time an infected person travels through the area.
 
Another important consideration is that the droplets of bleach in the spray can be corrosive and cause harmful respiratory effects when inhaled. Spraying should only be done when there are no people around.
 
However, a far more effective regime is to recommend stringent personal hygiene. This includes regular hand washing with soap and water and the use of alcohol-based sanitizer when hand washing isn't possible.
 
So, if spraying disinfectant in urban areas is unlikely to be effective, why are we seeing some countries doing this?
 
There are many reasons, one is that the authorities want to create an environment that is free from COVID-19 but aren't following the science. A more likely reason is to help people feel safe because they see authorities taking action.
 
It has been studied that in a crisis, people are less likely to take on board what ever… their current beliefs. Although the science indicates urban disinfection is probably ineffective, it's likely the general public believes otherwise. As a result, spraying city streets might have the effect of allaying fears and building trust in government and the messages it distributes. https://emergency.cdc.gov/cerc/ppt/CERC_Psychology_of_a_Crisis.pdf
 
However a possible downside of this is that people who feel their environment is safe might be less stringent about personal hygiene and physical distancing. These precautions are vital in preventing the virus spreading through the community; if people stop observing these behaviors, the virus is likely to spread much more quickly.
 
On the whole, while urban disinfection may increase public confidence, it is likely to be ineffective in protecting the public from infection.
 
For more on COVID-19 disinfectants and disinfecting services, keep logging to Thailand Medical News
 
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