HKU Bulletin November 2020 (Vol. 22 No.1)

Rigorous research is the key to understanding COVID-19 and getting its spread under control. Scholars in the Li Ka Shing Faculty of Medicine (HKUMed) are at the forefront of this research and have rightly received attention from around the world for their significant findings (see recent highlights on page 19). But scholars in other disciplines have also applied their expertise to reveal new characteristics about the pandemic. On these pages, engineering research shows how poor ventilation can increase risk of exposure to the virus, while business research shows how phone data can be used to track COVID-19’s spread in the population. COVID-19 : Tracking the Pandemic POOR VENTILATION HELPS THE VIRUS SPREAD A simple criterion for insufficient ventilation is if you can smell other people’s breath from a distance. Professor Yuguo Li HKU’s Department of Mechanical Engineering has shown that COVID-19 can be transmitted several metres by air when there is poor ventilation – a timely warning as winter approaches and people spend more time indoors. The finding came out of a detailed study of three COVID-19 outbreaks in crowded situations that looked at where infected individuals were located, who they infected and the rate of ventilation. The outbreaks were at a Guangzhou restaurant, two Hunan buses, and the Diamond Princess cruise ship from January to March, and the study was led by Professor Yuguo Li, Chair Professor of Building Environment, who previously played a key part in showing the role of ventilation in two clusters of cases during the 2003 SARS outbreak. At the Guangzhou restaurant, three families who did not know each other were sitting at adjacent tables. An index patient sat at one table and subsequently infected nine people at all three tables, including one person who sat 4.6 metres away. Subsequent measurements by Professor Li and his team showed the ventilation rate was only 1 L/s (one litre per second) per person, against the international standard of 5 L/s. Similarly, the Hunan buses were poorly ventilated. One index patient took a bus ride of three hours and 20 minutes that resulted in seven patients being infected, then took a second one-hour journey on a minibus in which two people were infected. The furthest infected person was 9.5 metres away from the index patient. The bus had a time- averaged ventilation rate of 1.7 L/s and the minibus 3.2 L/s. Keep the air moving On the Diamond Princess, which had more than 700 confirmed cases, the findings went the other way: the team showed that infection among passengers after the onset of quarantine was limited to those who had stayed in the same stateroom as an infected passenger. This probably meant the central air-conditioning system did not play a role, although the team were unable to get reference measurements. “In a sufficiently ventilated room, droplet concentrations in the exhaled jet of air from an infected person will continually decrease and become indistinguishable from background room air at a distance of about 1.5 metres. Our findings suggest that airborne transmission of the COVID-19 virus Professor Li is an expert in ventilation of indoor environments with a focus on environmental transmission of diseases. The path of airflow between the tables of the three families involved in the Guangzhou restaurant case. indoors is likely when the ventilation rate is less than 3 L/s per person,” Professor Li said. Public places should enhance indoor air ventilation and social gatherings indoors should be avoided if there is not sufficient ventilation, he said. A carbon dioxide sensor could help indicate poor ventilation if the reading is more than 1,000 parts per million. Otherwise, “a simple criterion for insufficient ventilation is if you can smell other people’s breath from a distance,” he added. 17 RESEARCH 16 The University of Hong Kong Bulletin | November 2020

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