On Jul. 15, 2020, in collaboration with the Guangdong CDC, Hunan CDC, Sun Yat-Sen University and Southeast University, Professor Yuguo Li, Chair Professor of Building Environment, and his team at the Department of Mechanical Engineering of the University of Hong Kong (HKU), conducted a series of epidemiological and environmental studies on three important Covid-19 outbreak cases in Mainland China and Tokyo, and revealed that poor air ventilation plays a key role in its spread in indoor environments.

Professor Li is an expert in ventilation of indoor environments with a focus on environmental transmission of diseases. During the SARS outbreak in 2003, Professor Li and a group of mechanical engineering experts at HKU developed an advanced mechanistic airflow model with computational fluid dynamics simulations and detailed thermo-fluid analyses to track and explain the main infection pattern and characteristics of the outbreak at Amoy Gardens and at Ward 8A of Princess of Wales Hospital.

The team studied three major outbreak cases that occurred between January and March 2020:

The Guangzhou Restaurant case (occurred on January 24, 2020) where nine members from three non-associated families sitting in three separate tables (A, B and C) were infected by an index patient at table A located in the middle. Four people in the same table, three people in table B on the left side of A, and two people in table C on the right side, were eventually infected. The three families did not know each other and had essentially no contact before, during or after the meal. The distance between the index patient (A1) and the furthest away infected patron was 4.6 metres.

The Hunan buses case (occurred on January 22, 2020) where an index patient took two buses subsequently from Changsha to his home village in an afternoon and eventually infected 10 passengers in total. first leg of the journey involved a bus with 46 other people (passengers/driver). The 3 hours 20 minutes’ ride resulted in seven passengers being infected. In the second journey on a minibus lasting about an hour, two out of 17 other people (passengers, driver and conductor) were infected. distance between the index patient (A1) and furthest away infected patron was 9.5 metres.

The Diamond Princess Cruise case in Tokyo (January to March 2020), where a total of 696 confirmed cases (552 passengers and 144 crew members, of those 410 were asymptomatic) were reported by March 5, 2020 among the 2,666 passengers undergoing quarantine in their staterooms and 1,045 crew members on board the ship.

“In both the Guangzhou Restaurant case and the Hunan buses case, there is evidence that airborne is the probable way of transmission of the virus, given that those infected were sitting at a distance, and quite a number of them more than 2m apart from the index patients, and no other transmission route can explain the spatial pattern of the infection. We found that a poor ventilation rate is a major contributing factor to the virus’ spreading in the environment.” Professor Li said.