Is spraying fungicides on the streets effective to prevent coronavirus?
With the spread of the 2019 coronavirus (COVID-19) pandemic, you may have seen photos and videos of workers wearing protective equipment using high-pressure spray to clean city streets. Spain even took radical measures to spray bleach on the beach. You may ask yourself if this really has a big impact on the risk of coronavirus transmission. If not, why should the government spend time, energy and funds to do this?
The effectiveness of spraying streets and other public places may depend on how the virus spreads, how the disinfectant works, and under what conditions.
How does the virus spread?
We now know that viruses mainly spread in two ways.
The first is through droplets and aerosols in the air, which come from infected individuals. These droplets are expelled into the air by coughing or sneezing, and can infect another person who comes into close contact with it. Larger water droplets will not stay in the air for a long time and will soon settle to the ground or other surfaces.
The aerosol is smaller and the suspension time is longer-up to 3 hours. Over time, the aerosol will dry out quickly and dissipate. This reduces the possibility of a person being infected by exposure to sufficient viral particles (ie, infectious dose).
The second method of disease transmission is through surface contamination. When the droplets settle, the virus can last for different times, depending on the nature of the surface. For example, a study found that the virus can survive 72 hours on plastic and stainless steel, 8 hours on copper, and 4 hours on porous surfaces such as cardboard.
However, this experiment was conducted under indoor laboratory conditions. So far, there is no information about how long the virus can survive outdoors. It is also unknown how likely you are to be infected when you walk on city streets.
How does disinfectant work?
We must also consider the process of disinfection. According to news reports, most authorities are using diluted bleach to disinfect urban areas. Studies have shown that the COVID-19 virus is sensitive to bleach, but it requires about a minute of contact time to be effective.
Even if the disinfectant reaches every outdoor surface that may be touched by people, including areas that are not affected by sprays, using bleach under typical outdoor conditions still has problems. Sunlight deactivates bleached active ingredients. This means that the disinfectant may have failed before the virus was killed.
For a virus to infect a person, it needs to enter the body. This happens when your hand touches the surface and is contaminated, and you put your hand on your face, near your nose or mouth. But when was the last time you touched the ground and face without washing your hands?
The average person rarely touches the city streets and sidewalks with their hands. This is another reason why spraying disinfectant on these surfaces is unlikely to be an effective control measure.
Commonly contacted surfaces, such as handrails and cross-road buttons, are more likely to be a source of infection, but must be cleaned before disinfection with bleach. This is because organic matter accumulates on the surface areas that are in frequent contact, including natural oils on human skin. Even if it is cleaned before disinfection, this process needs to be continued because the next time an infected person touches the surface, it may be contaminated again.
Spraying disinfectant into the air can reduce the amount of viruses suspended in the air. However, the effect is very limited because the disinfectant will quickly disperse. The next time the infected person passes the area, the aerosol will be introduced again.
Another consideration is that the bleach droplets in the spray can be corrosive and can cause harmful effects on the respiratory system after inhalation. Spray only when there are no people around.
A more effective method is to recommend strict personal hygiene. This includes washing your hands regularly with soap and water, and using alcohol-based hand sanitizer when it is impossible to wash your hands.
So why should the country spray the streets?
Therefore, if spraying disinfectants in urban areas is unlikely to be effective, why do we see some countries doing this?
There are two possibilities. First, the authorities wanted to create an environment without COVID-19, but did not follow science. The more likely reason is to help people feel safe because they see the authorities taking action.
In a crisis, people are unlikely to agree with current beliefs. Although science suggests that urban disinfection may be ineffective, the public may not think so. Therefore, spraying pesticides on city streets may have the effect of reducing fear and building trust in the government and the information it conveys.
However, one possible disadvantage of doing this is that those who think their environment is safe may be less strict about personal hygiene and physical distance. These precautions are essential to prevent the virus from spreading in the community; if people stop to observe these behaviors, the virus may spread faster.
The information from this is that although urban disinfection may increase public confidence, it may be ineffective in protecting the public from infection.
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