In the public perception of fluoride-transmission infections, there is often a misperception that it can spread no more than one metre. This perception makes it possible for many people to use only one metre as an absolute security standard while maintaining their social distance, but it is not that simple.
The spread of foam is one of the important modes of transmission of respiratory infections. When patients cough, sneeze and speak loudly, a large amount of foam is sprayed from the mouth and nose. These are larger in size, usually over 100 micrometres, and can sink faster to the ground as a result of gravity. Thus, in general, there is a higher risk of inhaling these foams when exposed at close range, e.g. within one metre. For example, during high-prevalence influenza seasons, people with influenza are exposed to infection if they are not masked. It is also an important basis for advocating for social distance of about a metre.
However, the distance from which the foam spreads cannot be defined in absolute terms within one metre. A number of special circumstances may lead to a further spread of foam. First, environmental factors play a key role. In poorly ventilated closed spaces, foams are difficult to spread and dilute rapidly, can stay in the air for longer periods and may spread further with the current. For example, in a small and closed elevator room, if an infectious patient coughs, the foam may echo in this relatively closed space, spreading far above a metre, or even reaching the corner of the elevator, putting other people in the elevator at risk of infection.
Second, the behaviour and physical characteristics of an individual can also affect the distance from which it spreads. When a person coughs or sneezes with greater power, and the initial speed of the spray is high, it is possible to overcome gravity and fly further away. For example, in patients with some respiratory diseases that cause more severe coughing, it is likely to eject up to two metres or more. Furthermore, if a cough or sneeze is not properly shielded, the foam spreads around, rather than in the direct front, which also increases the possibility of the foam spreading to a distance.
Moreover, the viability and spread characteristics of some viruses in the foams also allow them to cause infection more far away. For example, the new coronary virus can survive for a certain period of time, and in certain special circumstances, even if it is more than a metre from the patient, it may be infected if it is inhaled with the air containing the virus. Especially in densely populated locations, such as supermarkets, stations, etc., people frequently breathe and move, which complicates the flow of air, makes it even more difficult to predict the path of foam transmission and can affect people a metre away.
There is also considerable evidence of a distance of more than one metre from the actual epidemic. In some cases of indoor concentrated infections, the distance between some of the patients and the source of the infection was found to be more than one metre, but it is still infected, which further suggests that we cannot simply limit the distance from which the foam spreads to one metre.
While one metre of social distance has in many cases helped to reduce the risk of fluoride-transmission, we cannot afford to paralyze. During the epidemic, especially in closed and densely populated environments, in addition to maintaining appropriate social distances, we should wear masks, which can effectively prevent the spread of foam, whether close or relatively distant, and provide us with important protection. At the same time, increased indoor ventilation, the promotion of air circulation and the reduction of the time spent in the air by foam are important measures to prevent the spread of the infection.
The distance from which the infection spreads is not always more than one metre. We need to take a more scientific and holistic view of the spread of foam and take comprehensive measures of protection in our daily lives to better protect ourselves and others from respiratory infections.
