Student close contact behavior and COVID-19 transmission in China's classrooms
3University of Hong Kong 4Beijing University of Technology
5Clean Energy Research Institute, China Electric Power Planning and Engineering Institute
Abstract
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In this paper, we developed a wearable device for close contact behavior detection and recorded more than 250-thousand data points of close contact behaviors of students from Grades 1 through 12. Combined with a survey on students’ behaviors, virus transmission characteristics in classrooms was analyzed. We found that close contact rates for students were `37%\pm11%` during classes and `48%\pm13%` during breaks. Students in lower grades had higher close contact rates and virus transmission potential. The long-range airborne transmission route is dominant, accounting for `90%\pm3.6%` and `75%\pm7.7%` with and without mask wearing, respectively. During breaks, the short-range airborne route became more important, contributing `48%\pm3.1%` in grades 1 to 9 (without wearing masks). Our proposed human behavior detection and analysis methods offer a powerful tool to understand virus transmission characteristics, and can be employed in various indoor environments.
Students’ behavior characteristics in classroom
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During classes, face-to-back is the main orientation for close contacts because students usually face the blackboard and teacher. The probability of face-to-back close contact increases with grade level. During breaks, face-to-face was dominant. The absolute horizontal relative angles were usually concentrated between `5°~35°` during classes and `15°~25°` was the dominant relative angle range. During breaks, the absolute horizontal relative angles were usually concentrated between `5°~25°` and `5°~15°` was the dominant relative angle range. The vertical relative angle was usually concentrated between `-5°~25°` during both classes and breaks, with relatively few vertical angles being less than `-5°`. During breaks and classes, the talking rate generally decreased with increasing grade. English, Chinese, and Math class had average talking rates of `27%`, `25%`, and `15%`, respectively.
Virus transmission characteristics in classroom
Taking into account the school’s ventilation, the researchers estimate that most COVID-19 viral transmission in the school would be via long-distance airborne transmission, although short-range airborne transmission was more likely during breaks—but only when no masks were worn.
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Analysis of the influence of ventilation rate
The relative infection risk declined with increasing outdoor air ventilation rate, but this trend gradually flattened out. The absolute value of `\frac{∂(C//C_{base})}{∂Q}` changed little (`≤2%`) when the outdoor air ventilation rate exceeded `30 m^3`/`h`/`person`. Above this point, continually increasing outdoor air does not reduce the infection risk effectively, but consumes more energy. Therefore, we suggested a `30 m^3`/`h`/`person` outdoor air ventilation rate in classrooms.
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Check out our paper for more details.
Citation
@article{guo2023student, title={Student close contact behavior and COVID-19 transmission in China's classrooms}, author={Guo, Yong and Dou, Zhiyang and Zhang, Nan and Liu, Xiyue and Su, Boni and Li, Yuguo and Zhang, Yinping}, journal={PNAS Nexus}, volume={2}, number={5}, pages={pgad142}, year={2023}, publisher={Oxford University Press US} }