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Transcript of SHWF on the findings of an investigation of severe acute respiratory syndrome outbreak at Amoy Gardens (Part 1)


Following is the transcript of remarks by the Secretary for Health, Welfare and Food, Dr Yeoh Eng-kiong, at the press conference on the findings of the investigation into the outbreak of severe acute respiratory syndrome (SARS) at Amoy Gardens today (April 17):

Secretary for Health, Welfare and Food, Dr. Yeoh: In the past few weeks, we have put together a multi-disciplinary team of eight government departments to conduct a very detailed and thorough investigation into the outbreak of SARS at Amoy Gardens. I am particularly grateful to the Secretary for the Environment, Transport and Works, Dr Sarah Liao, who really offered her assistance and expertise on the environmental aspects of the investigation, and certainly to the other Government departments taking part. The investigation is all-embracive, covering epidemiological, environmental, public hygiene, building designs and utilities aspects. So, it is a very detailed and thorough investigation. We have completed our investigations and we are presenting our major findings today. However, before we go into the details of the findings, I think it is important for the public to understand that any investigation of this nature will always be conducted under some limitations, not least because we have an incomplete understanding of the disease and the need to minimise inconvenience and distress to the affected residents. Nonetheless, we are of the view that we have done all that is possible and looked into all the possible and probable causes of this outbreak at Amoy Gardens, and the findings help us identify effective actions to tackle the situation.

I shall now turn to the major findings, beginning with the epidemiological investigation. First, if you remember we have said that the index patient, the person that we believe was the source of the infection, was a 33-year-old man who lived in Shenzhen and visited his brother in Amoy Gardens regularly. This individual had chronic renal disease and was being treated at Prince of Wales Hospital. He developed symptoms of SARS on March 14, and on both March 14 and March 19, he visited his brother who is a resident of Block E of Amoy Gardens. He had diarrhoea at the time and had used the bathroom. His brother and sister-in-law and two nurses who attended to him at the Prince of Wales Hospital subsequently also developed SARS. As of the 15th of April we now have a total of 321 individuals affected by SARS who lived in Amoy Gardens. There is a very obvious concentration of individuals in Block E who were affected, accounting for 41per cent of these 321 cases. Other blocks in Amoy Gardens - if you remembered Block E has 33 floors with eight apartment units on each floor. Units 7 and 8 had the highest rates of infection. Seventy-three per cent of the units in Unit 8 had individuals who were infected by SARS, so the attack rate was 78 per cent. Unit 7 had 42 per cent of the units affected, so these were very high attack rates in Units 7 and 8 of Block E. So Block E has 8 units and there was a very high attack rate in both units 7 and 8. In terms of onset dates, the outbreak reached its peak on March 24 and declined steadily thereafter. Cases in Block E appeared earlier, generally about three days earlier, and in the outbreak, it showed a point-source type distribution - one event occurred and led to the contamination and all the infections followed that event. Cases in other blocks appeared three days later and were more evenly spread out in time. So when you look at the onset of illness, we believe that the patient was the initial source of infection. He infected a number of residents in Block E and then the rest of the residents in Block E. The other blocks in Amoy Gardens were affected about three days later. So when we look at the onset dates, there is a very clear time lag between the onset of infections in Block E and the onset of infections in the other blocks - a three-day time lag.

The Department of Health had also conducted a questionnaire to look at the common symptoms of SARS in this outbreak, and a very notable feature is that 66 per cent of all the patients who came down with SARS had diarrhoea. It also showed that four per cent had contacts with SARS patients and eight per cent had visited the Mainland during the period. So the very notable feature of this outbreak is that 66 per cent or two-thirds of the patients had diarrhoea.

I shall now turn to the environmental investigations. What we see is a very important and integral part of our overall investigation, and we need to explore and examine all possible and probable causes of this outbreak. I would like to give a summary of our findings. First, you can see that with each block, there are eight vertical soil stacks, each collecting effluent from the same units of all floors. The soil stack is connected with the water closets, the basins, the bathtubs and the bathroom floor drains. Each of these sanitary fixtures is fitted with a U-shape water trap, the U-trap. This U-trap prevents foul smells and insects in the soil stack from entering the bathroom. So, you have a U-shape water trap that is intended to be filled because once you fill it with water you don't get the reflux of the smells and the sewers back into the households. For this preventive measure to function properly, the water traps must be sufficiently filled with water. So, it's a very simple device. Interviews with Amoy Gardens residents revealed frequent complaints about foul smells in the bathrooms, which suggested that the U-trap arrangement might not be functioning properly in some units. As the water closets, the bath tubs and the basins were frequently used, their U-traps should be charged with water and should have been functioning properly. However, as most households have the habit of cleaning the bathroom floor by mopping instead of flushing with water, the U-traps connected to most floor drains were likely to be dry and were not functioning properly. In the test carried out by Dr Liao's team in one of the units in Block E, reflux of air from the soil stack into the bathroom to the floor drain was demonstrated when the exhaust fan in the bathroom was switched on. It can therefore be postulated that the reflux could have contained droplets of contaminated sewage present in the soil stack. The contaminated droplets were then dispersed into the bathroom. Dr Liao's team also conducted a tracer dye test on the sewage pipe, but no leakage was confirmed. However, by using an oil droplet test a crack in the sewer vent pipe at the fourth floor level was located. The vent pipe is connected to the branch soil pipe, to equalise the air pressure between the main soil stack and the branch soil stack. In theory, any leakage in the sewage system is important as it could allow droplets carrying contaminated sewage to be ejected into the lightwell. However, the amount of virus ejected and the velocity of the emission cannot be quantified. So there are these possible mechanisms where the sewage could really go into the flats through the mechanisms I've described.

We also saw signs of cockroach infestation in Amoy Gardens in particular around the carpark, food premises and drain openings. Rodent activities were also detected around refuse collection chambers, the carpark and food premises. So these were evidence of pest infestation. So this is part of the environmental investigation.

The third part is that we did laboratory investigations. A collection of air samples, water samples, environmental swabs and animal swabs droppings sera were taken in Amoy Gardens to identify the extent of the environmental contamination by the causative agent. No abnormalities were detected in the air and water samples. One environmental swab collected from the inner room of a toilet in Block E where a SARS patient is a resident was positive for the virus that we know causes SARS, the coronavirus. So we were able to detect in the toilet of one of the resident's flats, the presence of coronavirus. Coronavirus was also detected in the pest droppings and in some instances on the surfaces of the cockroaches. As the rodents showed no sign of infection or disease, the findings only point to environmental contamination at Amoy Gardens and pests are likely to be no more than mechanical carriers for the virus in this outbreak. So, because the rodents were not infected and there was no sign of disease, the finding demonstrates that all these findings are part and partial of the environmental contamination because it could have affected anyone who had been in physical contact with some of these environmental samplings. So these were just passive mechanical carriers.

(to be continued)

Thursday, April 17, 2003


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