Available on-demand - F.GI01.04.05
Late News: Characterizing Viral Lifetimes from Droplet-Surface Interactions
Junsang Yoon1,Jacob Myers2,Anand Srinivasan3,Fan Yang4,Miriam Rafailovich4
Cupertino High School1,The University of Scranton2,The Westminster Schools3,Stony Brook University, The State University of New York4
Show Abstract
SARS-CoV-2 (CoV) has sickened millions and killed hundreds of thousands since emerging less than a year ago. Aerosol transmission of CoV in respiratory droplets is well-established, but its capacity for fomite transmission is not well defined [1,2]. Fomite transmission of viruses are generally impacted by two factors: surface materials and droplet composition. However, both mechanisms are not well defined. For example, viral lifetimes may be affected by different surface-droplet interactions which influence the amount of water retained in a dried droplet residue, or through distribution patterns that create the localization of dried droplet solutes. Thus, this study aims to better characterize the expected lifetime of CoV by simulating various surface-droplet interactions frequent in real life.
Droplets of distilled water, saline, DMEM+10%FBS, lung fluid, and human saliva, with volumes ranging from 0.25 - 2.0 uL, were deposited onto paper, glass, polylactic acid (PLA), and aluminum. All samples were analyzed using contact angle goniometry and microbalance data; the changes in droplet volume over time were recorded, from which the evaporation rate and concentration of solutes were determined. Images of the drying pattern of each surface-droplet interaction were generated using confocal laser scanning. Plaque assays are now being performed at 10-minute time intervals to determine virus lifetimes.
Results indicate that the surface material greatly affects the drying rate. Significantly different evaporation rates were obtained when placing distilled water on aluminum, glass, and PLA. More importantly, fluids relevant to virus transmission, such as saliva and lung fluid, evaporated significantly slower on paper and faster on glass than they did on PLA and aluminum, with rabbit lung fluid evaporating at 0.164ul/min on glass and 0.051 ul/min on paper. Droplet composition also impacted the drying rates. Based on the contents of the droplets, two different drying mechanisms have been observed. Distilled water and human saliva dried at a linear rate, but in saline, DMEM+10%FBS and lung fluid, an initial linear decrease in volume followed by a slower asymptotic approach to the volume of the solutes was observed. Droplets with the asymptotic mechanism could keep viruses hydrated for a much longer time than previously predicted. Saline droplets retained 3.75% of their starting mass and porcine lung fluid retained 12.08% after 50 minutes, compared to 0.08% for water droplets after only 39 minutes. This contrast suggests increased hydration, and potentially lengthened virus lifetimes, for droplets that dry by the asymptotic mechanism. Images taken using confocal laser scanning show that both the surface and the composition of the liquid droplet affect the distribution of droplet solutes. On aluminum, glass, and PLA, droplets of saline and rabbit lung fluid showed a pinned contact line, leading to the buildup of solutes near the edge of the droplet, while saliva droplets created a buildup of solutes in the center of the droplet. The localization of solutes in saline, rabbit lung, and saliva droplets may also indicate an ability to hold water for a longer period of time.
Continued experiments using plaque assays of droplets and droplet residues containing H1N1 and the coronavirus OC43 deposited on different surfaces will reveal more directly the lifetime of CoV on different surfaces over time.
[1] Aboubakr HA, Sharafeldin TA, Goyal SM. Stability of SARS CoV 2 and other coronaviruses in the environment and on common touch surfaces and the influence of climatic conditions: A review. Transboundary and emerging diseases.
[2] Firquet, S., Beaujard, S., Lobert, P. E., Sané, F., Caloone, D., Izard, D., & Hober, D. (2015). Survival of Enveloped and Non-Enveloped Viruses on Inanimate Surfaces. Microbes and environments, 30(2), 140–144.
We gratefully acknowledge support from the Louis Morin Charitable Trust