Short-range airborne route dominates exposure of respiratory infection during close contact

Chen, Wenzhao; Zhang, Nan; Wei, Jianjian; Yen, Hui‐Ling; Li, Yuguo

doi:10.1101/2020.03.16.20037291

Cited by 107 publications

(198 citation statements)

References 49 publications

(57 reference statements)

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“…The trajectory of the exhaled respiratory droplets is affected by both the expired air flows profile and surrounding air flow patterns. Existing studies treated the exhaled air as a turbulent round jet [ 49 , 50 ], and the turbulent flow will enhance the heat and mass transfer between the droplet and the surrounding air. Therefore, respiratory droplets will likely evaporate faster than the simulated results in this study, and a larger fraction of respiratory droplets and viruses may remain airborne for a longer period of time.…”

Section: Resultsmentioning

confidence: 99%

Modeling the load of SARS-CoV-2 virus in human expelled particles during coughing and speaking

Wang

Huang

2020

PLoS ONE

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Particle size is an essential factor when considering the fate and transport of virus-containing droplets expelled by human, because it determines the deposition pattern in the human respiratory system and the evolution of droplets by evaporation and gravitational settling. However, the evolution of virus-containing droplets and the size-dependent viral load have not been studied in detail. The lack of this information leads to uncertainties in understanding the airborne transmission of respiratory diseases, such as the COVID-19. In this study, through a set of differential equations describing the evolution of respiratory droplets and by using the SARS-CoV-2 virus as an example, we investigated the distribution of airborne virus in human expelled particles from coughing and speaking. More specifically, by calculating the vertical distances traveled by the respiratory droplets, we examined the number of viruses that can remain airborne and the size of particles carrying these airborne viruses after different elapsed times. From a single cough, a person with a high viral load in respiratory fluid (2.35 × 10 9 copies per ml) may generate as many as 1.23 × 10 5 copies of viruses that can remain airborne after 10 seconds, compared to 386 copies of a normal patient (7.00 × 10 6 copies per ml). Masking, however, can effectively block around 94% of the viruses that may otherwise remain airborne after 10 seconds. Our study found that no clear size boundary exists between particles that can settle and can remain airborne. The results from this study challenge the conventional understanding of disease transmission routes through airborne and droplet mechanisms. We suggest that a complete understanding of the respiratory droplet evolution is essential and needed to identify the transmission mechanisms of respiratory diseases.

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Section: Resultsmentioning

confidence: 99%

Modeling the load of SARS-CoV-2 virus in human expelled particles during coughing and speaking

Wang

Huang

2020

PLoS ONE

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“…Second, our face can be contaminated by large droplets when we are in close contact with an infected individual 41 . Large droplets can be deposited on our mucous membranes as in the traditional large droplet route 42 , and they can also be deposited on other parts of our HFNS. Our nondominant hand switches between touching our mucous membranes and other parts of the HFNS, which can transmit microbes between them.…”

Section: Discussionmentioning

confidence: 99%

Most self-touches are with the nondominant hand

Zhang

Jia

Wang

et al. 2020

Sci Rep

Self Cite

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Self-touch may promote the transfer of microorganisms between body parts or surfaces to mucosa. In overt videography of a postgraduate office, students spent 9% of their time touching their own hair, face, neck, and shoulders (HFNS). These data were collected from 274,000 s of surveillance video in a Chinese graduate student office. The non-dominant hand contributed to 66.1% of HFNStouches. Most importantly, mucous membranes were touched, on average, 34.3 (SE = 2.4) times per hour, which the non-dominant hand contributed to 240% more than the dominant hand. Gender had no significant effect on touch frequency, but a significant effect on duration per touch. The duration per touch on the HFNS was fitted with a log-log linear distribution. Touch behaviour analysis included surface combinations and a probability matrix for sequential touches of 20 sub-surfaces. These findings may partly explain the observed variation in the literature regarding the microbiome community distribution on human skin, supporting the importance of indirect contact transmission route in some respiratory disease transmission and providing data for risk analysis of infection spread and control. It is known that some respiratory and enteric viruses, such as rhinovirus and norovirus may be transmitted by touching mucous membranes with our own contaminated hands 1-3 , and a vast number of bacteria thrive on human skin 4,5. Skin is one of the largest human-associated microbial habitats and harbours up to 1 × 10 7 bacteria per cm 2 of skin, which can have important effects on health 6,7. Average skin bacterial communities appear to be more diverse than those found in the throat, stomach or faecal environments 8. The hands play a critical role in microbiome transfer via frequent contact with contaminated environmental surfaces and a typical hand harbours more than 4,700 unique phylotypes 6. Average phylotype richness on a single palm surface is also more than three times higher than the variety observed in molecular surveys of both forearm skin 5 and elbow skin 9. The factors that drive this variability on the hand and skin bacterial community composition remain poorly understood 6,10. Age, hand and gender are intrinsic factors that affect the composition of the hand microbiome 6,11 due to the high variability in the population's skin humidity, acidity and nutrient level, sweat or sebum production, frequency of moisturiser or cosmetic application and skin thickness 12,13. It is known that touch can transfer microbes between hands and surfaces, but very little is known about human touch behaviour. A recent study showed that students touched surfaces with both hands for more than 90% of the observed time in their office, and more than 10% of touch time was on their own hair, face, neck and shoulders (HFNS) 14. These body surfaces can be contaminated by our own contaminated hands. Therefore, the distribution of touches to these surfaces is thus important. The importance of touch is also associated with the survival of microbes on the hands. Some enter...

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“…The model developed herein describes the risk of small respiratory drops (r < r c ) in the case where the entirety of the room is well mixed. There are undoubtedly circumstances where there are substantial spatial and temporal variations of the pathogen concentration from the mean 7,28 .…”

Section: Beyond the Well-mixed Roommentioning

confidence: 99%

Beyond Six Feet: A Guideline to Limit Indoor Airborne Transmission of COVID-19

Bazant

Bush

2020

Preprint

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The revival of the global economy is being predicated on the Six-Foot Rule, a guideline that offers little protection from pathogen-bearing droplets sufficiently small to be continuously mixed through an indoor space. The importance of indoor, airborne transmission of COVID-19 is now widely recognized; nevertheless, no quantitative measures have been proposed to protect against it. In this article, we build upon models of airborne disease transmission in order to derive a safety guideline that would impose a precise upper bound on the cumulative exposure time, the product of the number of occupants and their time in an enclosed space. We demonstrate the manner in which this bound depends on the ventilation rate and dimensions of the room; the breathing rate, respiratory activity and face-mask use of its occupants; and the infectiousness of the respiratory aerosols, a disease-specific parameter that we estimate from available data. Case studies are presented, implications for contact tracing considered, and appropriate caveats enumerated.

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Short-range airborne route dominates exposure of respiratory infection during close contact

Cited by 107 publications

References 49 publications

Modeling the load of SARS-CoV-2 virus in human expelled particles during coughing and speaking

Modeling the load of SARS-CoV-2 virus in human expelled particles during coughing and speaking

Most self-touches are with the nondominant hand

Beyond Six Feet: A Guideline to Limit Indoor Airborne Transmission of COVID-19

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