Updated: Sep 23
Anil Ananthaswamy published a recent article in Knowable Magazine that analyzes how pathogens or viruses spread from place to place and from person to person. The first thing to know is that understanding the dynamics of fluids is crucial to understanding the transmission of disease. Air is a fluid: bacteria and viruses are carried by fluids.
Lydia Bourouiba, fluid dynamicist from Massachusetts Institute of Technology (MIT) has been researching for more than ten years how fluids “can help disease move from one host or reservoir to the next”. Let’s review some key insight she gave to Knowable Magazine on how the dynamic of fluids can inform public health measures and help diminish the spread of infectious diseases, especially Covid-19.
How contagion works and prevention
Bourouiba affirms that whenever we’re talking about respiratory disease, the person always exhales pathogen-carrying droplets into the air. In order to cause infection to other people, these droplets need to be inhaled and reach the person’s tissue in the respiratory system. The process is dynamic, not static so in order to develop more policies to prevent, surveille and mitigate the spread of the disease it is crucial to have a dynamic thinking.
“For example, the fact that SARS-CoV-2–containing droplets can remain in the air for hours with the virus potentially still being viable and dispersed indoors means that healthcare workers caring for Covid-19 patients should use high-grade respirators, and they should be putting them on well before coming face-to-face with the infected individual, not just when they are within 6 feet of the patient”.
Policies: Should people wear masks?
Masks are an effective means of disease control. Fluids follow the path that offers the least resistance. For example, if a mask is not correctly sealed (and it’s open on the sides) “most of the fluid passes through the largest openings, not the mask’s filter material”. Encountering an obstacle does lower the exhalation cloud’s momentum, reducing its range as well, and the cloud can be overtaken by the room’s air flow. “If most of the flow passes through the mask’s filter, as happens in well-sealed masks, what comes out is a gas flow with lowered viral particle content”.
Is ventilation in indoor spaces effective in preventing the spread of the droplets?
Displacement ventilation can be better at ensuring that contaminants will stay in the upper part of the room, rather than in the breathing zone. “In displacement ventilation, cooler clean air is slowly injected from the floor or lower levels and exits from the ceiling or upper room levels”. Even if you cannot achieve displacement ventilation, sufficiently ventilating a room dilutes the viral matter in the air reducing the possibility of infection and/or infection with a high viral load.
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