How human thermal plume influences near-human transport of respiratory droplets and airborne particles: a review.

With mounting evidence and notable cases of large clustered infections, airborne transmission via droplets and particles has been recently acknowledged as an effective mode of transmission for COVID-19. How droplets and aerosol particles disperse are being transported into the human breathing zone-the last few inches for airborne transmission to effectuate-remains a key question which has been widely overlooked. Human thermal plume refers to the constantly rising airflows around the boundary layer of human body due to persisting temperature gradients between the body surfaces and the ambient air. Ample evidence indicated that the thermal plume controls the dispersion and transport of aerosols in the human microenvironment. Given that in calm indoor environments most air inhaled by human comes from the boundary layer where thermal plume flows through constantly, the role of thermal plume needs to be scrutinized to predict the diffusion of droplets, aerosols and other airborne carriers of the novel coronavirus around the human body for prioritizing infection control strategies. Here, we assessed the potential influences of the thermal plume on the transmission of COVID-19 and other airborne pathogens by reviewing the most pertinent evidence and analyzing key variables in the formation of thermal plume in indoor environments, e.g., ambient temperature, human posture and type of clothing. Our reviewed evidence and data indicate that the human thermal plume should facilitate the airborne transmission of COVID-19 in enclosed spaces by elevating small droplets and airborne particles into the breathing zone from lower regions and ascending respiratory droplets from the sources into the upper atmosphere. By drawing attention to aerosol transport dynamics in the human microenvironment, these insights may be useful for understanding COVID-19 transmission in enclosed spaces, especially those intended for public use.

Open defecation and squat toilets, an overlooked risk of fecal transmission of COVID-19 and other pathogens in developing communities.

The novel coronavirus disease COVID-19 has infected over 46 million people in 219 countries and territories. Following evidence of viral loadings and infectivity of feces of infected individuals, public health authorities have suggested to take precautions on the transmission of COVID-19 via fecal-associated routes. Recent discussions on fecal transmission of COVID-19 have mainly focused on municipal sewage. Yet, a widely neglected aspect in containing the virus is that a major part of the population in developing regions do not have access to private, clean sanitary facilities. Therefore, we hypothesize that open defecation and the prevalent use of squat toilets are additional risk factors in those communities. Here, we review fecal transmission of COVID-19, the practices of open defecation, and the resultant routes of transmission of fecal pathogens. Also, we highlight the open design of common squat toilets and the potential exposure to fecal droplets and residues. We observed that at least 20 countries reporting more than 10,000 confirmed infections have 5-26% of their population practicing open defecation. We illustrate the potential routes of transmission of COVID-19 and other fecal pathogens via human feces in communities practicing open defecation. Here, poor hand hygiene, contaminated shoes and objects, mechanical vectors, and outdoor human activities can all contribute to fecal transmission. Other risk factors include squat pans with lidless designs and open flushing mechanisms, in-cubicle open waste bins, and the lack of water-sealing U-traps in squat toilets.

Solar heating to inactivate thermal-sensitive pathogenic microorganisms in vehicles: application to COVID-19.

Disinfection is a common practice to inhibit pathogens, yet success is limited by microbial adaptation and our poor knowledge of viral transmission, notably in the current COVID-19 pandemic. There is a need for alternative disinfection strategies and techniques that are adapted to the actual behavior of humans living in densely populated mega-cities. Here, high public circulation in shared passenger vehicles such as taxis, buses and personal cars represents a major risk of viral transmission due to confined space and commonly touched surfaces. Actual regulatory guidelines are not fully successful because they rely both on passengers' willingness to wear face masks and on drivers' willingness to disinfect cars after each shift or each ride with symptomatic individuals. Here we propose that passive solar heating, a sustainable technique that has been used in agronomy to kill weeds and soil pathogens, could inactivate the virus in vehicles during warm-to-hot weather within few minutes to half an hour at 50-60 °C. We measured temperatures in a white compact-size sedan left in a parking lot under direct sunlight. Air temperatures increased from 30 to 42-49 °C after 30 min and then reached a plateau at 52-57 °C after 90 min. Temperatures were about 3 °C higher in front versus back of the car and about 5 °C higher at face height compared to knee height. Since COVID-19 is inactivated in 30 min at 56 °C, our findings confirm that hot air generated passively by solar heating in enclosed spaces is a promising strategy of disinfection with benefits of no added costs, chemicals or worktime. Though this technique appears limited to hot climate, possible heating systems that work during parking time might be developed by vehicle makers to extend the technique to cold climates.

Unflushable or missing toilet paper, the dilemma for developing communities during the COVID-19 episode.

Unlike in developed countries, most public toilets in China do not provide toilet paper onsite and users must bring their toilet paper. Moreover, an open waste bin is placed in each user's cubicle to collect used toilet paper and tissues. Such practices, which are common in East Asia and central America, have induced a dilemma of toilet paper disposal because some municipalities have removed waste bins from public toilets to prevent virus transmission by fecal matter. As a consequence, users were forced to flush down their used toilet paper and tissues. Yet, it is unknown whether standard toilet paper can be flushed easily without causing issues in sewer operations. Here, we surveyed the conditions of toilets in university campus and other public facilities in different regions across China. We also evaluated the disintegration characteristics of toilet paper products both by conducting online surveys and by physical disintegration experiments. We found that only 15% of toilets provided toilet paper, while open waste bins occurred at nearly all sites. Further, our survey indicated that 82% of toilet paper products sold in China did not give any indication on their flushability, whereas 77% of US products did. Disintegration results showed that none of the five popular, best-selling toilet paper products passed the flushability standard. We propose strategies to solve the current toilet paper dilemma in developing communities.