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Expert Group's advice on cryptosporidium
05/11/2002
The need for effective local measurement and response to cryptosporidium in water supplies has been emphasised by the Expert Group chaired by Professor Ian Bouchier.
The Group has ruled out a single national standard following the cryptosporidium incident in Glasgow in August this year.
It was responding to a request from Health Minister Malcolm Chisholm to give a further comment on the conclusion the Group had reached in 1998.
This was one of a series of recommendations made by the ad hoc group of Ministers chaired by Mr Chisholm which called for clearer guidance on the scientific criteria for assessing risk, better communication with the public and reinforcement of the lead role of local teams dealing with incidents.
Professor Bochier said his Group's conclusion remained the same as before - that it was not possible to recommend a single health-related standard for cryptosporidium in drinking water.
In his reply, Professor Bouchier states:
"The Group recognises that infective dose is a huge variable, depending, inter alia, on host susceptibility and oocyst source, species, age and condition. Some research has been undertaken since the Group's last report but this has confirmed that it is not possible to predict infective dose for any particular circumstance.
"The Group therefore concluded that, on current evidence, its advice is still valid and that whenever oocysts are detected or suspected of contaminating a drinking water supply any actions or decisions must be based on local risk assessment, knowledge and experience."
On the question of informing the public about levels of cryptosporidium and the need to boil water, Professor Bouchier states:
"Again, the Group concluded that there is no definitive trigger level for deciding on these matters as they will need to be based on a series of judgements taking into account the local circumstances. The Group does recommend that such decisions are decided only by a formally convened Incident Control Team."
Professor Bouchier underlined the need for adequate and well operated treatment in form of physical barriers to minimise the number of oocysts entering the distribution system.
Dr Andrew Fraser, Deputy Chief Medical Officer at the Scottish Executive, said:
"I am grateful to Professor Bouchier for convening his Expert Group and responding to the Minister's request. Both the Executive and I agree with Professor Bouchier that there needs to be a continuing focus on improving filtration of high risk public water supplies such as that to Glasgow.
"Until improved filtration is in place, effective risk assessment will continue to be a high priority and his response reminds us that knowledge, experience and judgement are the skills that Incident Control Teams bring together with local information in assessing risks to the public from cryptosporidium. We are committed to further strengthening the ways in which public health, water and other experts assess and control these risks, and to communicating with the public so that they can take informed decisions on their own part. In the light of Professor Bouchier's letter, I am amending guidance to reflect the Expert Group's advice."
The Executive agrees with Professor Bouchier that there needs to be a continuing focus on improving filtration of high risk public supplies such as in Glasgow. Ministers cannot comment on specific plans or locations due to the current appeal by Scottish Water against the decision by East Dunbartonshire Council to refuse planning permission for a new water
treatment works at Milngavie. However, Ministers have made clear on several occasions the importance of upgrading filtration of the Glasgow water supply to reduce risk of infection and improve protection for public health.
The ad-hoc ministerial group was established within days of the Glasgow incident. It called for clearer guidance on the scientific criteria for assessing risk, better communication with the public and reinforcing the lead role of local teams dealing with incidents
The Executive has issued interim guidelines to NHS Boards on public health responses to the detection of cryptosporidium in drinking water supplies. Guidance will be revised in the light of the Expert Group's comments.
Incident control teams in Aberdeen, Glasgow and Edinburgh are expected to publish their reports later this month.
Professor Ian Bouchier CBE is a distinguished gastroenterologist and former Professor of Medicine at Edinburgh University. From 1992 to 1997 he was Chief Scientist in the Scottish Health Department.
The full text of Professor Bouchier's letter:
THE EXPERT GROUP ON CRYPTOSPORIDIUM IN WATER SUPPLIES
Chairman: Professor Ian Bouchier CBE
Mr M Chisholm MSP
Minister for Health and Community Care
St Andrew's House
Regent Road
Edinburgh EH1 3DG 31 October 2002
Dear Mr Chisholm
EXPERT GROUP ON CRYPTOSPORIDIUM IN WATER SUPPLIES
You wrote to me in August after the establishment of an Incident Control Team and a decision to issue advice to boil drinking water to parts of Glasgow following the detection of Cryptosporidium oocysts in the water supply. You requested that my Expert Group should consider whether any further advice on incident management was appropriate in the light of
experience since the publication of its last report in 1998, especially in respect of three particular issues which caused concern or difficulty in interpretation.
The Expert Group met in Edinburgh in October 2002 and gave very careful consideration to the issues you raised. I set out the Group's response to the issues below in the same order as your letter.
However, firstly I wish to emphasise the need for sources of drinking water that are at significant risk from Cryptosporidium oocysts to receive adequate and well operated treatment in the form of physical barriers that will minimise the number of oocysts entering the distribution system. I understand the water supply to Glasgow involved in the August event does not yet have this protection and until it is in place, uncertainty and the possibility of risk of infection will remain.
The first issue concerned further consideration and comment on the Group's 1998 conclusion that it is not possible to recommend a health-related standard for Cryptosporidium in drinking water. The Group recognises that infective dose is a huge variable depending, inter alia, on host susceptibility and oocyst source, species, age and condition. Some research has been undertaken since the Group's last report but this has confirmed that it is not possible to predict infective dose for any particular circumstance. The Group therefore concluded that, on current evidence, its advice is still valid and that whenever oocysts are detected or suspected of contaminating a drinking water supply any actions or decisions must be based on local risk assessment, knowledge and experience.
The Group again recommends that it is vital that the parties likely to be involved in an Incident Control Team continually share background knowledge and maintain good communications so that, as far as possible, they are not presented with unrehearsed scenarios.
The second issue related to informing the public about levels of Cryptosporidium and the need to boil water. Again, the Group concluded that there is no definitive trigger level for deciding on these matters as they will need to be based on a series of judgements taking into account the local circumstances. The Group does recommend that such decisions are decided only by a formally convened Incident Control Team.
The third issue is whether current advice in relation to immuno-compromised people remains relevant. This Group's 1998 advice was refined subsequently by medical experts convened by the Department of Health in London and published in the Chief Medical Officer's Bulletin. More scientific papers have been published subsequently but there has been nothing to change the Group's view on this issue although it will keep it under review.
The Group also considered the Scottish Executive Health Department's interim guidance on public health action following the detection of raised levels of Cryptosporidium in public drinking water supplies in Scotland and will be sending comments directly to the Department. I look forward to receiving formal reports on the recent outbreak of cryptosporidiosis in Aberdeen and the events in Glasgow and Edinburgh so that the Group may consider if there are wider lessons to be drawn.
Yours sincerely
I Bouchier CBE
Chairman
Expert Group on Cryptosporidium in Water Supplies