Scottish Government

Introduction

1. In Scotland, deaths from diseases caused by drinking water are very rare and diseases caused by drinking water are relatively uncommon and almost always mild. They are nowhere near as common or severe as those associated with diet for example. In most interpretations of the word, the public drinking water supply is safe. However it always has the potential to cause widespread ill health if something goes wrong. Because of this vigilance is essential. Increasing vigilance has led to improvements in monitoring of the public water supply. As a result we have needed to develop risk assessment processes to interpret the public health significance of the detection of higher than expected levels of a range of waterborne hazards, in particular cryptosporidium oocysts. Communicating to the public the risks associated with waterborne oocysts and what needs to be done to reduce these risks can be difficult. There is need therefore to make the processes involved in dealing with these issues more transparent.

2. The purpose of the guidance is to inform:

• the development of the Scottish Waterborne Hazard Incident Plan (SWHIP) and local plans and procedures based on this;

• the functions of the Incident Control teams set up to deal with such incidents.

It has been drawn up with input from the Scottish Centre for Infection and Environmental Health. Its contents have been discussed with a range of interested parties involved in public health and the water industry. Specialist advice on its contents have been obtained from the UK Group of Experts on Cryptosporidium in Water Supplies (which advises UK Health Departments) and other professional groups. The guidance follows the tenets of SEHD guidance on managing public health incidents.

Background

3. Cryptosporidium is a parasite which lives in a wide range of domestic and wild animals. It is excreted in the faeces of infected animals and humans in the form of oocysts (tiny spore-like structures which have a protective coating enabling them to resist chlorine and other forms of disinfection). These oocysts are easily carried in water and may be present in low concentrations in many environmental waters and also less frequently in treated (disinfected and filtered) water for human consumption.

4. One species of the parasite, Cryptosporidium parvum, is most commonly associated with human infection. In normal healthy individuals this usually causes an acute, self-limiting, mild diarrhoeal illness (cryptosporidiosis), which on average starts 2-10 days after exposure to the organism and lasts for up to 4 weeks. Infection rates are highest in the under fives. Its main public health importance lies in the severe illness caused in certain immuno-compromised individuals, the lack of an effective specific drug treatment and the potential for outbreaks, especially large waterborne outbreaks.

5. Transmission to humans of C ryptosporidium parvum is by faecal/oral spread, the main routes of which are person to person; animal to person; drinking water; ingesting water from swimming pools and occasionally via food, milk, or, rarely, healthcare. It is not unusual for the cause of cases of cryptosporidiosis occurring in a community to remain unclear. Human illness is usually more common in spring and autumn: this has been associated with increased shedding of high-viability oocysts by lambs and other livestock, and with heavy rainfall. The average annual number of reported human cases in Scotland is approximately 800.

6. Cryptosporidium oocysts should be removed by the modern, well operated methods used in most water treatment works in Scotland. However a number of water treatment works in Scotland do not have the relevant filtration systems for removing oocysts. The most notable of these is the Milngavie water treatment works that serves Greater Glasgow. A major capital investment is being made to install these systems. Until these are in place, these water supplies require special monitoring and, wherever possible, alternative risk reduction measures e.g. in the catchment area involved. Scottish Water is required by the Cryptosporidium Direction (issued to them by the Executive in February 2000 and revised in April 2002) to assess the risks associated with the sources of public drinking water. Where this risk is categorised as high, Scottish Water is required to monitor the presence of these oocysts in the treated drinking water. All water treatment methods (filtration and disinfection), however, can be subject to failure or may be compromised when dealing with very high levels of naturally occurring contaminants in the water. Contingency planning for this possibility is therefore essential.

7. The installation of monitoring mechanisms and especially the introduction of more sensitive sampling methods have resulted in greater awareness of the occurrence of oocysts in raw and treated water. This in turn has given rise to debate about what action is required following the detection of raised levels of oocysts. The issue has been discussed by the Group of Experts on Cryptosporidium in Water Supplies and an ad-hoc working group of the Public Health Laboratory Service Advisory Committee on Water and the Environment. In summary the groups found that:

• it is not possible currently to define accurately the relationship between oocyst counts in treated water and the health risk to those who drink it;

• outbreaks of cryptosporidiosis in which epidemiological evidence is strongly indicative of waterborne spread, have been found to occur when raised concentrations of oocysts in treated drinking water have not been detected;

• there is a strong correlation between the occurrence of outbreaks and situations where water treatment systems are inadequate (e.g. lack appropriate filtration systems) or faults have occurred in their operation or when they have become overloaded (as can occur following heavy rainfall and run off from agricultural land into water courses).

8. The Group of Experts on Cryptosporidium in Water Supplies therefore concluded in 1998 that "it is not possible to recommend a health related standard for cryptosporidium in drinking water". In August 2002, the Minister for Health and Community Care asked the Group for further comment on this statement in the light of any scientific advances in the interim. The Group discussed the relevant issues and concluded that there was no need to change from its 1998 position.

Risk assessment, management and communication

9. The Cryptosporidium Direction 2000 requires that Scottish Water reports to the relevant NHS Board, any finding of one or more oocysts in any 10 litre sample of treated water. In addition Scottish Water is in a position to identify actual or potential problems with water quality which could have implications for public health. NHS Boards are in a position to identify outbreaks of cryptosporidiosis and other illnesses which may be due to drinking contaminated water. Scottish Water and NHS Boards are in on-going communications about these problems. Recent events have indicated the need to further specify the circumstances which should trigger the direct involvement of public health professionals in assessing the risks to the public from drinking water. They also confirm the need for systems which ensure a mutual response to actual or potential problems in water quality with public health implications.

10. Based on local agreement founded on information of background levels, when raised levels of oocysts for a given water supply are detected in raw or treated drinking water, a risk assessment and management process should be adopted. This is summarised in Appendix A. The steps involved are:

• problem identification;

• problem investigation;

• risk assessment;

• risk management; and

• risk communication.

11. In the normal course of events, unless a decision can safely be taken that following the problem identification and initial investigation stages, no further action is warranted, the processes of risk assessment and management should be co-ordinated through jointly agreed procedures defined in the SWHIP and local NHS Boards' incident plans. These should be based on SEHD guidance on managing public health incidents. Response to the detection should be flexible. If there is imminent significant risk to the public health, urgent action to reduce risk may be necessary. In the case of the latter, as indicated in current SEHD guidance, risk assessment and control measures may be put in place before the ICT convenes. In such instances, Scottish Water and the Public Health Department should maintain close contact and on-going dialogue over risk and control measures. However unless significant risk is imminent an ICT should be called. Meetings should be short and kept to a minimum, with due regard to the requirement for appropriate discussion and consultation.

12. Low oocyst counts are routinely detected in some treated water supplies, especially if the supply is not filtered and if high volume continuous monitoring systems are employed. The ad-hoc working group of the Public Health Laboratory Service (PHLS) Advisory Committee on Water and the Environment therefore advised that the level of oocyst count triggering urgent reporting should depend on the history of a given supply both in terms of its counts, where available, and the dependability of its treatment processes. The sensitivity and reliability of laboratory testing should also be considered alongside recent improvements in detection methods. Agreement on these action "triggers" should be reached between water utilities and public health departments, ideally prior to an incident occurring. These will indicate the need for further work to investigate the problem, assess risk and if necessary, take risk reduction measures.

Problem identification

13. Scottish Water should inform the relevant NHS Board Public Health Department(s) and the Local Authority Department(s) responsible for environmental health in a population served by a given water supply about problems of water quality of public health significance, in particular:

• the detection of raised levels of cryptosporidium oocysts in treated water;

• significant failures in any water treatment processes, especially those with the potential to lead to increased levels of oocysts in drinking water, and the expected length of time necessary to remedy these. Guidance on what constitutes a significant failure is contained in a letter dated 1 October 2001 from the Water Services Unit at the Scottish Executive to the 3 former water authorities;

Due regard should be given to instances which could lead to overloading of the treatment processes, such as very heavy rainfall and excessive run off from catchment area land, or to significant changes in agricultural practices on land adjacent to catchment area or aqueducts.

14. NHS Boards should ensure that they have procedures to ensure that on being alerted information is passed to senior management, and in particular to the Board Press Officer.

15. Expert advice on these issues is available from the SCIEH, which should be informed of potential problems.

Problem investigation

16. The NHS Board Public Health Department(s) should liase with Scottish Water in the investigation. Scottish Water should collate information on:

• Concentrations of oocysts in the water, trends in them and the sampling and testing methods by which these are measured;

• The type and efficacy of the water treatment processes;

• the distribution of drinking water supplied, factors influencing the dilution of any contaminated water and the residence time of the water in the affected parts of the distribution system;

• The size and location of the population to which drinking water is distributed and the past and current incidence of cryptosporidiosis in it;

• the likelihood of water bypassing the treatment processes.

17. Annex 1 provides details of the questions which should be considered during the initial problem investigation phase. Should there be any question about the efficacy of water treatment processes, the Drinking Water Quality Unit should be contacted and requested to carry out an urgent independent audit of the treatment processes involved.

18. Of particular importance in investigating an incident is the accurate and prompt laboratory testing of oocysts in water and their subsequent speciation and typing. Scottish Water should liase with NHS Boards and others in ensuring that laboratories involved in these processes are accredited for the purpose and have sufficient capacity to react to the surge in demand for testing arising from such incidents.

Health Risk Assessment

19. The purpose of the health risk assessment is to decide, when a change in the level of cryptosporidium oocysts has occurred in a public water supply, if there is an increased probability of cryptosporidiosis in the population served.

20. Risk assessment essentially entails appraising the balance of evidence collected in the problem investigation and reaching a view as to whether it indicates that there is a significant threat to public health. Cryptosporidium levels, water treatment and supply factors and the numbers of people likely to be exposed to the increased levels of the organism should be reviewed. The probability of infection occurring in susceptible groups in the population e.g. children, consuming average quantities of tap water should be considered. In all these areas, there are considerable gaps in current scientific knowledge, leading to a range of uncertainties impinging on decision-making. Conclusions derived from this process are principally a matter of professional judgement.

21. For reasons of public accountability and understanding, it is essential that decisions taken about risk are as transparent as possible. The outcome of risk assessments must therefore be clearly recorded, including :

• the loading of cryptosporidium in the raw water and whether this is known to be normal or exceptional due to adverse weather events or an increased environmental load e.g. that associated with lambing;

• the efficacy of water treatment processes involved in reducing levels of cryptosporidium oocysts;

• the concentration of cryptosporidium oocysts in the treated water involved and their significance e.g. are they high compared to historical trends for the supply;

• the likelihood of the population involved being exposed to raised levels of cryptosporidium oocysts;

• the probability of infection in the average individual and particularly in the young and immuno-compromised at risk of exposure from drinking water.

22. The outcome of risk assessment will vary according to the nature, timing and location of the problem identified. In broad terms, there are three likely outcomes of these assessments:

• Yes - there is an increased probability of cryptosporidiosis in the population served;

• There is insufficient evidence to indicate that there is an increased probability of cryptosporidiosis in the population served;

• No - there is no increased probability of cryptosporidiosis in the population served.

23. With regard to the first outcome (i.e. there may be an increased probability of cryptosporidiosis in the population served), the ad-hoc working group of the Public Health Laboratory Service Advisory Committee on Water and the Environment suggested that the following factors are indicative:

• a history of waterborne outbreaks associated with the same source;

• high oocyst counts in consecutive samples of treated water from the same source;

• other evidence of treatment failure;

• an increase in turbidity in treated water for that supply.

24. The ad-hoc Working Group indicates that the circumstances in which these factors are likely to occur together are likely to be uncommon.

Risk Management

25. The purpose of risk management is to put in place control measures to reduce the probability of increased numbers of cases of cryptosporidiosis occurring in a population served by a water supply with raised levels of cryptosporidium detected.

26. If control measures are to be taken, an Incident Control Team should normally be formed. As indicated above, immediate control measures need not await a formal ICT meeting. Decision-making on risk control measures should always be carried out expeditiously with unnecessary delays avoided.

27. The range of possible scenarios is such that it is difficult to prescribe the circumstances under which a specific control measure should be taken. Decision on the reasons for taking specific control measures should be recorded including the criteria necessary for removing them. These criteria should relate to the factors included in the risk assessment. The agency responsible for a specific control measure should check that the measure is being put in place in the time required and is having the desired effect. It should report on this to the Incident Control Team.

28. If the risk assessment indicates that there may be an increased probability of cryptosporidiosis in the population served, one or more of the following control measures should be put in place:

• rerouting of the mains water distribution system to provide an alternative supply of drinking water;

• issuing advice to boil water;

• provision of water by bottled water supplies;

• alert to healthcare services;

• enhanced monitoring of water quality;

• enhanced epidemiological surveillance;

• ongoing risk assessment.

29. For certain populations, Scottish Water should have in place as part of their contingency planning arrangements, procedures to secure the provision of an alternative water supply where this is practicable. This may involve using different water sources and distribution networks. For small rural populations, distributing bottled water may be an alternative. However there are significant logistical problems with this. Putting in place such arrangements usually takes some time and there are limitations in the scale of provision. Priority will be given to people with special needs.

30. Advice to boil water may be issued if an alternative supply of drinking water cannot be secured. There are a number of risks associated with issuing a boil water notice. Water only requires to be brought to the boil and should be allowed to cool in a safe place before drinking. There is very little research on the health gain associated with this measure. Compliance with the advice is estimated be less than 50%. It has been suggested that it could lead to an increase in scalds. Advice to boil water should only be given after appraising these risks against the public health benefits of the measure. It should not become a default position but should be reserved for situations where the level of risk to public health justifies it. Clear criteria for withdrawal of the boil notice should be established prior to its being issued: these criteria are likely to relate to, for example, re-establishing normal filter operation or, especially in the case of unfiltered supplies, subsequent oocyst concentrations.

31. Once a decision is made this must be communicated as widely as possible to the public with a high degree of urgency . Because of this, logistical arrangements for issuing such a notice should be agreed as part of SWHIP and local NHS plans prior to an incident occurring. The logistical arrangements will vary according to circumstances. They should be regularly tested .

Risk Communication

32. Risk communication is an essential part of the process of managing incidents involving the detection of cryptosporidium oocysts in water. Because the main issues to be covered in communications concern the level of risk to the public health, NHS Boards should take the lead in decision-making on risk communication. SEHD Guidance on the management of public health incidents makes it clear that this process should be based on a presumption in favour of openness. Decisions on risk communication should be recorded. Decisions not to communicate about actual or potential risks to the public health even when these are uncertain should be justified and recorded.

33. Scottish Water and NHS Boards should have a communications plan which indicates how they will provide information about the outbreak/incident and its control to the following key groups:

• the key agencies involved in managing the outbreak and relevant Scottish Executive Departments, the Drinking Water Regulator and the Water Industry Commissioner;

• primary and secondary health care and other professionals involved in diagnosing and treating cases of cryptosporidiosis and the immuno-compromised;

• the general public and in particular the communities directly affected by the incident.

34. With regard to the last, they should draw up locally agreed procedures for carrying out one or more of the following (or other communication channels which may be deemed appropriate):

• face to face communication with affected individuals or businesses (notably food and drink manufacturers or other food premises);

• the establishment of a helpline;

• letters or fact sheets provided directly to members of the public in an affected community;

• specially designed information leaflets to be distributed at appropriate points

• briefing key members of the public such as head teachers, MSPs, councillors, members of local health council

• information in the form of statements, press releases, interviews and briefings for the print and electronic media.

35. Communication systems need to be ready for use prior to any incident occurring and capable of rapid deployment. They should include pre-formulated general information on cryptosporidiosis and its association with drinking water. Local NHS Boards and Scottish Water should draw up procedures for prompt risk communication and regularly test them.

36. In cryptosporidium incidents, Scottish Water will have existing lines of communication to its business and private customers. Use of these lines of communication will facilitate advising the public on whether their supply is affected by raised levels of oocysts and in providing practical advice as to how they can reduce any risks associated with drinking water. The ICT should agree with Scottish Water how its resources will be used in this area and should co-ordinate the content and tone of any messages.

37. Key to communicating with the public is how the above processes are co-ordinated. Effective media handling is of particular importance. The SWHIP and local procedures based on it should as far as possible follow SEHD guidance on managing public health incidents. In particular the ICT should agree who will act as spokesman for the ICT and which Press Officer will liase with the media to ensure that the information communicated to them is consistent and to organise arrangements for press briefings, interviews etc.. Normally these will be the Chair of the ICT and the NHS Board Press Officer. In some instances however it will be desirable for Scottish Water to respond to press enquiries which specifically relate to its operations or legal responsibilities. The ICT should agree arrangements so that Scottish Water can respond promptly to such enquiries without straying from the core message about public health risks and the measures being taken to reduce them. Again the Chair of the ICT should be informed and full liaison with the agreed Press Officer maintained.

Formal reporting and communications

38. NHS Boards on being alerted to a problem with water quality, which is assessed as having the potential to lead to the formation of an incident control team, should urgently inform the Scottish Executive Health Department and the Scottish Centre for Infection and Environmental Health (SCIEH). SEHD should then receive regular updates on progress including copies of press releases. Consistent with the requirements of the Cryptosporidium Direction, Scottish Water should urgently inform the Drinking Water Quality Unit of any positive result from testing of treated water. The DWQU should also be informed urgently about the formation of an incident control team.

39. SEHD and DWQU will on receipt of a notification, copy all relevant information to each other and liase with their respective press offices. Agreement will be reached as to which Department leads on briefing ministers and on establishing clear channels of communication between the Executive and the ICT. These channels will be notified to all concerned and should be the sole lines of communication. The SE and ICT will agree the frequency and timing of updates on progress.

40. The lead SE Department will inform other SE and UK Departments e.g. the Food Standards Agency as appropriate.

41. All ICT reports on waterborne incidents should be copied to SEHD and DWQU as soon as possible after the incident is declared over. Appended to the report should be an action plan indicating how the NHS Board will follow up the recommendations included in the report.

Conclusion

42. Decision making on the risks to public health and how to control them is often a complex task. What to do following the detection of cryptosporidium oocysts in treated water is one such situation. This guidance aims to facilitate the risk management process and aid public understanding of the steps involved.

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Annex 1

Problem Investigation - questions to be considered

Detection of Cryptosporidium in Treated Drinking Water

• The circumstances under which the sample was taken, when, where and why - was it in response to a specific incident at a treatment works etc.

• The number of oocysts detected (per 10 litres) in treated water representing what is in public distribution.

• The number of oocysts in raw water representing the upstream load on the treatment process (taking into consideration how representative the sampling procedure employed is likely to be).

• Is the result from treated water a single positive or one of a trend?

• What is the Cryptosporidium sampling history for the supply and how do the present results compare?

• What sort of sample was taken: grab sample (10 litres) or continuous filter (100s litres)?

• How robust is the information? Does the initial laboratory result require confirmation?

• Is there confirmation that the oocysts were C. parvum and were viable (NB speciation of oocysts normally takes several days, hence this information is very unlikely to be available in the early stages of an incident and information on viability may not be available at all)?

• Regardless of oocyst viability, does the presence of oocysts indicate a treatment failure?

Water Supply and Treatment Issues

• Has there been a period of exceptionally high rainfall?

• What sort of water source was involved (groundwater, surface water)?

• What is the catchment area history e.g. presence of cattle, sheep and other livestock?

• What is known about potential vulnerable points such as aqueducts and hazards such as septic tanks, drainage water etc. leaking into distribution systems pre or post treatment?

• What sort of treatment system is in use (slow sand filtration, rapid gravity filtration or none)?

• Had there been any recent changes to the treatment process (planned maintenance, accidents)?

• Were there any associated indications of a treatment process problem, especially signs of increased turbidity in the final treated water?

• Has there been a technical problem and has it been resolved?

• Is there evidence of any ongoing technical problems?

• What is the history of the system in terms of previous problems and characteristics?

Water Distribution System

• What are the storage and distribution characteristics of the supply?

• Is there up to date information on the distribution zones and any areas where there is doubts about the exact supply source?

• What is the distribution area and how many people are being supplied?

• Where is any potentially contaminated water in the system at this point in time?

• What action has the water authority taken so far?

Epidemiology of Cryptosporidiosis Locally

• Has there been any increase in laboratory confirmed cases of Cryptosporidiosis in the local community?

• Have there been waterborne outbreaks of Cryptosporidium associated with this supply in the past?

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Appendix A - see interim guidance and/or hard copy.