Quantifying the size-resolved dynamics of indoor bioaerosol transport and control

Abstract

Understanding the bioaerosol dynamics of droplets and droplet nuclei emitted during respiratory activities is important for understanding how infectious diseases are transmitted and potentially controlled. To this end, we conducted experiments to quantify the size-resolved dynamics of indoor bioaerosol transport and control in an unoccupied apartment unit operating under four different HVAC particle filtration conditions. Two model organisms (Escherichia coli K12 and bacteriophage T4) were aerosolized under alternating low and high flow rates to roughly represent constant breathing and periodic coughing. Size-resolved aerosol sampling and settle plate swabbing were conducted in multiple locations. Samples were analyzed by DNA extraction and quantitative polymerase chain reaction (qPCR). DNA from both organisms was detected during all test conditions in all air samples up to 7 m away from the source, but decreased in magnitude with the distance from the source. A greater fraction of T4 DNA was recovered from the aerosol size fractions smaller than 1 μm than E. coli K12 at all air sampling locations. Higher efficiency HVAC filtration also reduced the amount of DNA recovered in air samples and on settle plates located 3-7 m from the source.

Short-range bioaerosol deposition and recovery of viable viruses and bacteria on surfaces from a cough and implications for respiratory disease transmission

“…Both the distributions and the peak positions along the surface were similar, meaning that the micro-organisms inside the droplets did not affect the droplet deposition on near surfaces. This was different from some of the research works in the literature (Wong et al 2010;Kunkel et al 2017), which showed that the bacteria or viruses inside the droplets can affect the deposition because of the irregular shapes of the airborne nuclei. In this work, for short-range situations, the evaporation process was not completed before deposition, so most of the airborne droplets were larger than 10 mm in diameter.…”

“…E. coli is the Gram-negative rod-shaped bacterium with typical size of 0.5-2 mm, and the phage is a double-stranded DNA coliphage and the characteristic size is about 60-200 nm. They are commonly used as the surrogates of bacterium and virus respectively in experimental studies (Kunkel et al 2017;Lai et al 2018;Yoon et al 2007).…”

“…The supernatant was centrifuged again at 28,000 g for 30 min. The bacteriophage pellet left at the bottom was then suspended into the buffer solution and the high titer phage T3 solution was then stored in a refrigerator at 4 C. The detailed protocol can be found in reference (Kunkel et al 2017). But in the last step, the phage pellet was resuspended into the Tris buffer [in g/L: Tris, 6.05, PH 7.4; NaCl, 5.8; MgSO 4 Á7H 2 O, 2] instead of the albumin-dextrose-saline (ADS) solution to avoid changing the wetting property of the solution.…”

“…There were more viable bacteria at the floor section near the wall opposite to the injection point than other areas. Kunkel et al (2017) studied the sizeresolved dynamics of coughing bioaerosol transportation and deposition within three rooms in one apartment (0.5 m, 3 m, and 5 m away). They showed that the largest Escherichia coli weight happened at 0.5 m and decreased as the distance increased, while the largest phage (virus) weight appeared at 3 m and the smallest weight was at 0.5 m on horizontal settling plates near the floor.…”

“…However, these studies focused on airborne aerosol deposition at rather long-range situations with relatively low aerosol velocity (Lai and Nazaroff 2000;Zhao and Wu 2007). In these situations, the microorganisms inside the airborne aerosol can affect the aerodynamics and deposition on floor surfaces (Wong et al 2010;Kunkel et al 2017). For a short-range direct deposition onto a surface from a cough with relatively high velocity, it is still unknown whether the bacteria or viruses inside the aerosol would affect the deposition or not.…”