Also said that the new crown virus aerosol transmission: the outbreak of SARS epidemic in Amoy Garden, Hong Kong in 2003 Selected
2020-4-7 11:54Read:15634Tags:coronavirus, aerosol transmission, Hong Kong, TaoDa Garden, SARS
It is also said that the new crown virus aerosol transmission: in 2003, the SARS epidemic broke out in Taoda Garden, Hong Kong
Because of my focus on atmospheric diffusion, I am sensitive to the problem of aerosol propagation. In early February, there was a wave of discussion [1], as exemplified by the outbreak of mass SARS virus infection in Amoy Garden, Hong Kong in 2003. For this purpose, some information is collected, studied and analyzed. But the hot discussion quickly dissipated, so I put it aside. Now it seems that the battle with the new crown virus may be repeated and will last for a long time. Aerosol transmission of the virus is likely to be discussed again. I would like to talk about my views for the reference of netizens:
In 2003, the SARS epidemic in Amoy Garden, Hong Kong, broke out in a concentrated manner, and the only reasonable explanation seems to be that the aerosol-transmitted virus process occurred.
Therefore, the main point was the formation of high-intensity toxic aerosols at that time and the special transport and spread conditions, which led to the outbreak of the epidemic.
l However, there are still doubts.
1. The outbreak time is short, the spatial distribution is concentrated and special, and the pollution source is strong
Amoy Garden Hong Kong is a dense cluster of 19 high-rise residential buildings, with the largest building spacing of only 60 meters. The building is 33 storeys high, and each floor is symmetrically distributed with 8 units (numbered 1 to 8), which are divided into 4 pairs according to the orientation, such as 7 and 8 units are a pair. In the middle of each pair of units is built a bottom-up (narrow and deep, very high) lightwell, flanked by restaurant and bathroom windows and exhaust fans, as well as vertically laid sewage pipes. The SARS outbreak began in Unit 7, 16th Floor, Block E: On 19 March, a visitor with a sick overnight stay had diarrhea (patient zero. He was hospitalized in a nearby hospital and was later confirmed to have infected two nurses with SARS). The number of confirmed patients increased day by day in the next three days, and the outbreak occurred on March 24, and by April 15, all 321 confirmed patients occurred in Taoda Garden, of which more than 200 patients (i.e. two-thirds) occurred in 4 days from March 24 to 27. Most of the patients are in Block E, which is concentrated in units 7 and 8 on each floor above 10 floors. The three nearby buildings B, C and D were significantly affected, followed by F and G.
It can be seen that the outbreak time of this epidemic is short, the spatial distribution is concentrated and special, and the pollution source is strong. According to the survey, the residents are not familiar with each other and rarely interact with each other. According to the setting and use of elevators, as well as the activity of insects and mice related to solid waste, it is difficult to explain the intensity and spatio-temporal distribution of the outbreak process only due to close contact or due to the form of cockroach and mouse activity [2]. In addition, 66% of SARS patients in Amoy Garden had diarrhea (up to more than 6 times a day) [3], which not only pointed to patient Zero in Block E (diarrhea is not the main disease of SARS), but also indicated that the sewage pipes had been seriously polluted. On March 21, due to inlet pipe repairs, Unit 8 began to stop supplying water from top to bottom for 16 hours at night. As a result, the "aerosolization" of the relevant sewage pipes containing virus-containing fecal water may occur, becoming a powerful source of pollution.
The Department of Health of the Hong Kong Government conducted on-site investigations and experiments, including the release of fine oil droplets in the light well and the sulfur hexafluoride experiment (to study the chimney effect, atmospheric diffusion trajectory), and the exhaust fan exhaust of the toilet in the unit. It was also found that the ventilation system of the 4-story sewage pipe in Block E was ruptured and there was sewage leakage. Although it is not considered to be directly related to the outbreak, it shows that there is a ventilation process in the sewage pipe, which may be beneficial to the aerosolization of fecal water, especially in the middle and upper sections of the sewage pipe. The conclusion at the time was [4]:
L At the outbreak of the epidemic, the U-shaped pipes connected to the water leakage on the floor of most unit bathrooms were dried for a long time and did not play the function of sealing the sewage system. When the occupants turn on the exhaust fan and close the bathroom door, the negative pressure generated causes the particulate matter in the sewage system to be sucked in, causing bathroom pollution.
l As a result of damage to the water supply system, all floors and 8 units in Block E were shut down for the night on 21 March. It is very likely to reduce the flow in the sewage system and enhance the production and movement of particulate matter in it. At the same time, flushing water with a bucket will increase the generation of sewage droplets in the bathroom.
The exhaust fan can transport the virus-carrying water droplets and particles present and generated in the bathroom to the light well outside the window. With the natural air flow in the light well, it can be transported to the windows of each unit above into higher levels, contaminating the unit.
The WHO Investigation Team subsequently supported this conclusion.
2. Introduce the problems existing in the "communication route map" of Internet celebrities:
The following "Map of Propagation Pathways" [1] has four drawbacks or errors: the bathroom is too spacious, the location of the terrace drainage is not clear, the "Lightwell" is too weakly drawn, and the labels of Units 7 and 8 are reversed.

The actual bathroom is small, only 3.5 square meters. Poorly designed for floor drains: the base of the side wall located under the window is not on the ground, and there is no cover. Residents are unlikely to wash with water and basically use mops, so the U-shaped tube is dry for a long time. As shown in the figure:

Amoy Garden is a dense high-rise residential area with flawed building design. The "light well" is only 1.5 meters wide, 5 meters deep, and nearly 100 meters high (4th to 36th floors, 33rd floors for households). Such a light well momentum is not drawn:

The original image came from the network, and I made changes
Take a look at the momentum of the tall buildings in Taoda Garden:
3. Spatial distribution of the epidemic

The original image is from the article [5] of Yu et al. The authors applied computational fluid dynamics software to calculate the vertical and horizontal spread of viral aerosols during outbreaks. I added sectional views of Units 7 and 8 in Block E, and Patient Zero 's location (red dot), visible toilets and narrow light well profiles. The figure on the floor side of the figure is the number of households where the patient is sick (removing the infection situation within the family). The infection of the buildings near Block E in the figure is visible and consistent with the possible effects of atmospheric spread under the northeast wind.
4. The Hong Kong Observatory summarizes the meteorological elements during the outbreak [6]:
At that time, the temperature was around 20 degrees, and the humidity was around 75% to 85%, which was suitable for the virus to survive. The wind direction continues for many days with the northeast wind dominant, as shown below, supporting the possible distribution of the atmospheric diffusion above.

It can be seen that the various conditions for aerosol-borne viruses are met.
5, there are still doubts
There is no direct evidence or experimental verification of the above "aerosolization" of the virus fecal water contained in the sewage pipe.
In particular, the suspension of water supply in Block E on the 21st was a key factor in the aerosolization of the virus-containing liquid in the sewage pipe. However, it was Unit 8 that stopped the water and Patient Zero stayed in Unit 7. The sewer pipes of the two units are arranged vertically and are not related to each other. Therefore, if the aerosolization process occurs, there is no direct relationship with patient zero. It can only be assumed that during the stay of Patient Zero, the virus was infected by close contact with the occupants of Unit 8 (e.g. elevator room). The infected patient also had multiple episodes of diarrhea that contaminated the bathroom and sewer pipes of Unit 8.
6. Conclusion:
l Regarding the SARS outbreak in Amoy Garden, Hong Kong in 2003, although there are doubts, the occurrence of viral aerosol transmission process is still the most reasonable explanation;
Many coincidences have contributed to the occurrence of aerosol transmission: SARS patients stay overnight with diarrhea, tall buildings with narrow and deep light wells, restaurant and bathroom windows and discharge fans facing light wells, bathroom platform water leakage elbow long-term drying, sewage pipes are high and long and ventilated, water supply is stopped for 16 hours, temperature and humidity are suitable for virus survival, wind direction is northeast, and high-rise buildings are small.
For the current COVID-19 epidemic, it is recommended that Hong Kong pay attention to the lessons learned from Amoy Garden.
For the rest of the continent, similar multi-factor "coincidence" events are almost unlikely. The chances of aerosols spreading the coronavirus are slim.
Resources
1. Zhang Yanmei, 2020, Aerosol-borne Coronavirus, How Do You Protect Yourself when You Return to Work? ScienceNet blog post, http://blog.sciencenet.cn/blog-3420875-1217782.html
2. Stephen K C Ng 2003, Possible role of an animal vector in the SARS outbreak at Amoy Gardens, THE LANCET, Vol 362, 570-572
3. Abdullah, Abu S.M. et al., 2003, Lessons from the Severe Acute Respiratory Syndrome Outbreak in Hong Kong, Emerging Infectious Diseases, Vol. 9, No. 9, 1042-1045
4. Department of Health, Hong Kong Government. 2003, Outbreak of Severe Acute Respiratory Syndrome (SARS) at Amoy Gardens, Kowloon Bay, Hong Kong. Main Findings of the Investigation.
5. Yu,ITS,et al.,2004,Evidence of Airborne Transmission of the Severe Acute Respiratory Syndrome Virus，New England Journal of Medicine, v. 350 n. 17, p. 1731-1739
6. W L Chang, K H Yeung, Y K Leung, 2005: Climate, Severe Acute Respiratory Syndrome (SARS) and Avian Flu，Hong Kong Observatory Report, Reprint 611