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Report of the consensus conference on Cryptosporidium in Water, Melbourne, October 1998
IntroductionThe Cryptosporidium in Water conference, held in Melbourne in October 1998, provided an overview of the current scientific knowledge on Cryptosporidium, and an opportunity to discuss the needs for future research, public health strategy, and risk assessment and management for water supplies.
More than 290 delegates from diverse backgrounds in water supply and management, parasitology, general microbiology, epidemiology and public health attended the conference.
The conference was divided into three themes, each with its own objective:
- Parasitology and genetic typing, to introduce genetic typing to assist in locating the source of the parasite;
- Epidemiology, to improve epidemiological surveillance, outbreak management and public health response; and
- Risk assessment and management, to understand and manage the health risks implied by Cryptosporidium monitoring results.
On the day following the general conference, small groups of experts continued discussions on each theme, with the aim of arriving at consensus positions on parasitology research needs, public health strategy and risk management principles. The deliberations and conclusions of the Epidemiology workshop group are summarised in the following Consensus Statement.
Consensus Statement: Epidemiology workshop groupDiscussions led to the identification of a number of areas of research priority as well as the need to develop rational public health policies despite the current limitations in our understanding. The group agreed that the primary aims of public health in relation to Cryptosporidium in water supplies are to:
- control disease;
- only intervene when needed; and
- use public funds as efficiently as possible.
Research prioritiesThe research priorities agreed by the group highlighted the current inadequate understanding of the natural history of the disease in humans, the nature and role of the immune response and the determinants of disease.
It was agreed that in this current state of uncertainty, there is a need to invest in well-targeted research that:
- will help us to understand the natural history of the disease and its immunology;
- explores the factors which enhance transmission of the infection in humans and the risk factors which predispose to that infection; and
- explores the effect of prior serological experience on infection outcomes.
Phenotyping or genotyping of strainsIt was agreed that considerable effort should go into developing methods for routine phenotyping or genotyping of strains isolated from humans and from water. Such techniques would represent a significant advance in epidemiology by allowing us to trace the origins of individual strains, and determine the importance of drinking water relative to other routes of transmission.
Viability and pathogenicityThere is also a great need for improved tests to determine the viability and pathogenicity of oocysts isolated from the environment so that we can better assess the degree of health risk posed by oocysts detected in drinking water.
Methods of treatmentThere is also a need for continuing efforts to develop effective methods of treatment of people with known infection. The availability of such treatment would markedly reduce the risks associated with infection in immunocompromised individuals, and would significantly change the public health perspective on this organism.
Community educationThere is clearly a need for better community education to improve the understanding of the disease, and to permit the effective protection of the community without promoting panic. It is important that we make efforts to explain our current limited knowledge of these issues, and the difficulties in predicting health risks from water testing results. We must also endeavour to use scarce public health resources as efficiently as possible.
Protocol for surveillanceIt is believed there is a need to develop a national best practice protocol for surveillance that is based on standard advice to laboratories regarding which stool specimens to examine, which methods to use, and the minimum notification data that should be passed on to public health agencies when the organism is identified. General practitioners around Australia should be advised by public health agencies on which cases to request stools for, and the most common risk factors, as they are currently understood, in this condition. At present there are considerable variations in testing practices and reporting procedures between different States and Territories which makes it difficult to establish a comprehensive picture. There is also a need for a validated system of multiplier values to relate the number of laboratory defined cases to the number of cases in the community.
Surveillance will only work effectively if improved partnerships are developed between public health units and water authorities, and if there are agreed triggers for enhanced surveillance. It is believed that increased water turbidity events and the presence of contamination with other pathogens may be appropriate triggers for enhanced surveillance for Cryptosporidial infection. Enhanced surveillance should include a systematic approach to elevated rates of diarrhoeal illness in nursing homes and other institutions, a follow-up of individual cases of cryptosporidiosis, active contact with laboratories, and possible activation of other sentinel systems, including school absenteeism, general practice systems and oncology units. Geographic Information Systems mapping of such data may be useful as an adjunct to identify and track outbreaks. The National Communicable Diseases Network is seen as the appropriate forum to progress these improvements in surveillance mechanisms for Cryptosporidium.
Outbreak investigationsOn the issue of investigation of suspected waterborne outbreaks, the group was not convinced that case control methodology is always the best approach to conducting investigations. A clear specification of the relevant investigative questions requires input from both public health as well as water authorities, and this may require brainstorming and application of cutting-edge technology. It is emphasised that while outbreaks of illness are undesirable, they nevertheless represent opportunities to improve our knowledge. The opportunity should be taken to store faecal and blood specimens, and it should be expected that each outbreak will help us further to understand the natural history of the disease. Finally, there is a need for national and international collaboration in outbreak investigations, including the standardisation of questionnaires used.
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Monitoring Cryptosporidium in finished waterIn the review of Sydney events, it became evident that the workshop group and others have been puzzled by the huge oocyst counts reported in finished water, with no detectable evidence of increased disease despite substantial enhancement of surveillance. It is noted that the availability of the technical capacity to detect Cryptosporidium in finished water makes it difficult for water authorities to avoid monitoring, but it is emphasised that the Sydney episode underlines our inability to interpret such findings. This is perhaps due to technology being ahead of medical science.
Multiple 'boil water' alerts can have hazardous results both in terms of injury risks to the community, loss of credibility for water and health authorities, and community outrage. The workshop group emphasised the view that, at present, public health is not a reason for monitoring Cryptosporidium numbers in finished water. Given the current state of testing technology, the viability or infectivity of oocysts cannot be determined, and therefore such counts cannot be used as a basis for public health action. However, it is recognised that such monitoring may serve a purpose for the water industry in assessing the effectiveness of water treatment processes for the removal of Cryptosporidium oocysts, and in identifying environmental factors which lead to elevations in oocyst numbers.
The group believed that a better approach to the monitoring of treated water would be careful investigation of all turbidity events. Changes in turbidity of treated water requires collaborative discussions with health personnel, review of water treatment procedures, and possibly introduction of enhanced surveillance when raw water Cryptosporidium counts are raised. When Cryptosporidium counts on treated water are elevated, it cannot be assumed that they necessarily constitute a significant public health hazard without extensive accompanying data and advice from a range of experts. Thus the detection of such events should not automatically trigger a 'boil water' alert, but instead trigger investigations by water and health officials to determine the causes and consider the need for such an alert to be issued.
The available evidence on natural history indicates that several oocysts are needed to infect people with normal immune function, but it is not clear whether people with significantly impaired immune function might be infected with lower numbers, perhaps even with one oocyst. Few (if any) water authorities can guarantee complete freedom from such a risk from using finished water, given the current state of technology.
Swimming poolsFinally, it was agreed that Cryptosporidium constitutes a substantial public health hazard in swimming pools, and that this risk will continue while parents take young children to pools in the summer. The only approaches identified as being available were public education to minimise contamination of pools, improved engineering of pool filters, and overnight hyperchlorination of affected filters and pools. Pool closures are as undesirable for the recreational water industry as 'boil water' alerts are for the drinking water industry, and may create similar public responses. While there is some scope for reducing the problem by better design and operation of pools, it is clear that the major need is for better public understanding of the issue.
Public health strategy for drinking waterThere was further discussion of the consensus public health strategy for drinking water in the final plenary session, with the following points being agreed:
- Relevant health and water industry personnel should have frequent routine contact so that rapid and effective consultation can take place whenever unusual water quality events occur.
- A stepwise response protocol should be established depending on the degree of health concern associated with different circumstances.
- It is important that the response protocol agreed between health and water authorities is subject to public comment during its development.
- The final response protocol must be made available to the public and the media. The protocol should set out the circumstances that would trigger a response, the investigative and corrective measures to be implemented for various levels of response, and the time period required to carry them out. Placing this information in the public domain in advance of any water quality events helps to address industry concerns over 'duty of care' with respect to the time taken for confirmatory testing and investigations.
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Author affiliation1. Director, National Centre for Epidemiology and Population Health, Australian National University, Canberra and CRC for Water Quality and Treatment.
2. Corresponding author and Senior Research Fellow, Department of Epidemiology and Preventive Medicine, Monash Medical School, Alfred Hospital, Prahran Victoria 3181, and CRC for Water Quality and Treatment.
Conference Proceedings can be obtained from the CRC for Water Quality and Treatment, PMB 3, Salisbury, South Australia 5108. Fax: 08 8259 0228
Sponsored by the Cooperative Research Centre for Water Quality and Treatment, the Water Services Association of Australia, the Australian Water and Wastewater Association,with additional support from the Department of Human Services Victoria
This article was published in Communicable Diseases Intelligence Volume 23, No 6, 10 June 1999.
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