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Cryptosporidiosis in the immunocompromised: weighing up the risk

Current evidence does not support a permanent "boil water" alert for all immunocompromised groups

Paul M Byleveld, Amanda Hunt and Jeremy M McAnulty

MJA 1999; 171: 426-428
See also Fairley et al

Synopsis - Introduction - Transmission risks - Recommendations - Conclusion - References - Authors' details
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Synopsis
  • Cryptosporidiosis has been increasingly recognised as a cause of diarrhoeal illness in both immunocompetent and immunocompromised people.
  • Massive outbreaks have been linked to municipal drinking water supplies in North America and Europe, but so far none have been reported in Australia.
  • There is evidence that modes of transmission other than drinking water are more important.
  • There can be no guarantee that infective Cryptosporidium oocysts will not contaminate an Australian water supply. Therefore, a permanent "boil water" warning may be warranted on medical advice in severely immunocompromised people, for whom cryptosporidiosis could be persistent and life threatening.

Introduction Between July and September 1998, drinking water in Sydney was contaminated with the protozoan parasites Cryptosporidium and Giardia. Human illness with cryptosporidiosis had been notifiable by laboratories in New South Wales since 1996, but giardiasis was not. In response to the contamination, surveillance for diarrhoeal disease was enhanced and residents in affected areas were advised to boil all drinking water. To determine whether the incidence of diarrhoeal illness had increased, NSW Health's six public health units in Sydney regularly contacted laboratories, general practitioners, emergency departments, pharmacies and nursing homes. In addition, NSW Health conducted telephone surveys of households to determine the residents' disease experience and compliance with warnings. At times during the contamination events, a proportion of the population was exposed to drinking water containing apparently high concentrations of Cryptosporidium and Giardia, because the water reached houses before the contamination was identified and because of poor compliance with the "boil water" alert. Despite this, there was no outbreak of disease attributable to drinking water, as indicated by increases in cases of diarrhoeal disease presenting to emergency departments, sentinel general practices or nursing homes, or laboratory reports of cryptosporidiosis.1

The Sydney Water Inquiry was established in August 1998 to investigate the causes of contamination and management of the incidents and to make recommendations about the control and prevention of such events. The Inquiry recommended that a permanent warning be issued to immunocompromised persons to boil all tap water before use, and that advice be provided on the risks of contracting cryptosporidiosis from water and other sources.2 The permanent "boil water" recommendation is a very cautious reaction to a threat that may be small, but is consistent with advice offered in the United Kingdom.3 The implementation of such advice would have a serious effect on the operation and costs for healthcare facilities and the food industry, if required to buy in treated water or provide additional treatments for water used for drinking or as ingredients.

In contrast to the recent Sydney experience of high oocyst counts but no detectable disease, large community-wide outbreaks of cryptosporidiosis have occurred in Britain and the United States following contamination of drinking water with concentrations of Cryptosporidium oocysts that were apparently much lower than those in Sydney.4,5 In Britain and the US, several outbreaks of waterborne cryptosporidiosis have resulted in significant morbidity and mortality in people infected with HIV (Box 1).6-8 Other classes of severely immunocompromised persons, including transplant recipients and patients receiving chemotherapy, may also be at greater risk from water contaminated with Cryptosporidium. While the available data are limited, the attack rate in these groups does not appear to be as high as that in those with HIV.6,7 The identification of waterborne disease is more likely in the immunocompromised, as these people may have prolonged illness and receive closer medical surveillance.

Compared with Cryptosporidium, the risk posed by Giardia and viral and bacterial pathogens to immunocompromised people from municipal water supplies is thought to be lower, because conventional water treatment processes (including chlorination) more easily control them.14

Transmission risks
The public and many clinicians poorly understand the relative importance of transmission of Cryptosporidium by drinking water compared with other modes of transmission (Box 2). Recent evidence shows that contaminated swimming pools are likely to pose a greater risk than a public water supply for the waterborne transmission of human infective forms of C. parvum.18,19

There have been no documented outbreaks of cryptosporidiosis or giardiasis associated with municipal water supplies in Australia. For waterborne transmission to occur, viable human-infective forms of C. parvum must be present in sufficient (albeit small) numbers. Available data to date suggest that parasites found in Sydney drinking water and originating from the catchments may not have been infectious to humans.1 However, the potential for transmission of Cryptosporidium and Giardia by drinking water in Australia was demonstrated at a campsite in Victoria, when guests developed cryptosporidiosis and giardiasis after an inground water tank was contaminated by effluent from a septic tank.20

In regional areas, the risk of waterborne cryptosporidiosis and giardiasis may vary from town to town. While the data are scarce, there is currently no evidence to suggest that immunocompromised persons who reside in these areas and receive an appropriately treated drinking water supply are at greater risk. Precautions should be taken with untreated water supplies, particularly those obtained from surface sources (rivers, creeks and dams). In New South Wales, a number of water suppliers have collaborated with health authorities to evaluate the risk of contamination from "catchment to tap". This process -- which involves assessments of (i) the risks to the water catchment area from sources including septic tanks, sewage overflows and agricultural activities, (ii) the integrity of the water treatment processes, and (iii) the distribution system -- better equips water suppliers and health authorities to provide information on local drinking water quality to clinicians and the public.

Recommendations
Since well before the recent contamination incidents, NSW Health has stated that people living with HIV and AIDS, those receiving treatment for some types of cancer and transplant recipients may (after consulting with their doctor) choose to avoid unboiled drinking water.21 Although evidence to date suggests that appropriately treated drinking water in New South Wales does not place anyone at risk of cryptosporidiosis, this advice is offered as a precautionary measure and is consistent with that offered by the US Centers for Disease Control and Prevention.22

Particular care should be taken with drinking water and food at remote accommodation facilities. Boiling is the most effective way to kill Cryptosporidium (and other pathogens) in drinking water, while many, but not all, filters and bottled water meet satisfactory standards.

Consumers should carefully examine the labels on filters and bottled water and seek an assurance from manufacturers that their products will protect against waterborne cryptosporidiosis and giardiasis. Water treatment units that incorporate boiling, distillation or reverse osmosis processes are satisfactory. Suitable filters include those labelled "absolute 1 micron" (or smaller) and certified to meet the relevant standard for cyst removal (either ANSI/NSF5323 or AS/NZS434824), but require an additional disinfection unit to inactivate bacterial and viral pathogens. Filters are likely to fail if not maintained in accordance with manufacturer's instructions. Because filters may accumulate pathogens, it is advisable to wear gloves and wash hands after changing filters.

It should not be assumed that all bottled water, beverages reconstituted with tap water and ice products are free from contamination. Mineral (or spring) water obtained from well-protected sources should not contain Cryptosporidium and Giardia. Other packaged water and ice products that are treated by distillation, reverse osmosis, or filtering through an absolute 1 micron (or smaller) filter should be free of Cryptosporidium and Giardia.

Data available to date have not provided evidence of local drinking water borne cryptosporidiosis and do not support a permanent "boil water" warning for all immunocompromised persons in New South Wales. Although the risk is likely to remain low, there can be no guarantee that infective Cryptosporidium oocysts will not contaminate an Australian water supply. Therefore, a permanent "boil water" warning may be warranted on medical advice in severely immunocompromised people, for whom cryptosporidiosis could be persistent and life threatening. Such people should also be advised to take great care with all other potential risk factors. Given the broad range and dynamic nature of these conditions, it is impossible for health authorities to list all classes of people who should receive this warning. Individual advice can only be provided by a doctor after considering the patient's status and case history.

The potential effect of a permanent boil water advice on quality of life for immunocompromised persons should be weighed up against benefits that may be gained. Factors to consider include the need to avoid a range of foods and beverages that may contain tap water, the risk of burns and scalds, and ongoing costs where filters or bottled water are used.

Conclusion Health departments rely on the diagnosis and timely notification of diarrhoeal disease and monitoring of water quality to protect the public from waterborne disease outbreaks. Where a reasonable threat to public health is likely to exist, the public is advised to boil drinking water. The recent events suggest that the risk of transmission of cryptosporidiosis by drinking water in Sydney may be very low, and highlight the limitations of water-testing techniques that do not define viability or human infectivity. But more is to be learnt about Cryptosporidium and the risk that it poses to the community. It is essential that health agencies continue to monitor and investigate clusters of cryptosporidiosis cases to learn more about modes of transmission and risk factors. Sound public health decisions can only be made on such evidence.

References
  1. NSW Department of Health. The Sydney Water Incident: July-September 1998. NSW Public Health Bulletin 1998; 9: 91-94.
  2. McClellan P. Sydney Water Inquiry. Final Report. Sydney: NSW Premier's Department, 1998.
  3. Bouchier IAD. Cryptosporidium in water supplies. 8. Advice to the immunocompromised individual. <http://www.dwi.detr.gov.uk/crypto/bou008.htm>. UK Drinking Water Inspectorate, Department of the Environment, Transport and Regions, 1998. Accessed 16 September 1999.
  4. Atherton F, Newman CPS, Casemore DP. An outbreak of waterborne cryptosporidiosis associated with a public water supply in the UK. Epidemiol Infect 1995; 115: 123-131.
  5. MacKenzie WR, Hoxie NJ, Proctor ME, et al. A massive outbreak in Milwaukee of Cryptosporidium infection transmitted through the public water supply. N Engl J Med 1994; 331: 161-167.
  6. Clifford CP, Crook DW, Conlon CP, et al. Impact of waterborne outbreak of cryptosporidiosis on AIDS and renal transplant patients. Lancet 1990; 335: 1455-1456.
  7. Goldstein ST, Juranek DD, Ravenholt O, et al. Cryptosporidiosis: an outbreak associated with drinking water despite state-of-the-art water treatment. Ann Intern Med 1996; 124: 459-468.
  8. Hoxie NJ, Davis JP, Vergeront JM, et al. Cryptosporidiosis-associated mortality following a massive waterborne outbreak in Milwaukee, Wisconsin. Am J Public Health 1997; 87: 2032-2035.
  9. National Centre in HIV Epidemiology and Clinical Research. HIV/AIDS and related diseases in Australia: Annual Surveillance Report 1998. Sydney: National Centre in HIV Epidemiology and Clinical Research, 1998. Available at <http://www.med.unsw.edu.au/nchecr>.
  10. Detels R, Munoz A, McFarlane G, et al. Effectiveness of potent antiretroviral therapy on time to AIDS and death in men with known HIV infection duration. Multicenter AIDS Cohort Study Investigators. JAMA 1998; 280: 1497-1503.
  11. Correll PK, Law MG, McDonald AM, et al. HIV disease progression in Australia in the time of combination antiretroviral therapies. Med J Aust 1998; 169: 469-472.
  12. Carr A, Marriot D, Field A, et al. Treatment of HIV-1-associated microsporidiosis and cryptosporidiosis with combination antiretroviral therapy. Lancet 1998; 351: 256-261.
  13. Foudraine NA, Weverling GJ, van Gool T, et al. Improvement of chronic diarrhoea in patients with advanced HIV-1 infection during potent antiretroviral therapy. AIDS 1998; 12: 35-41.
  14. National Health and Medical Research Council, and Agriculture and Resource Management Council of Australia and New Zealand. Australian Drinking Water Guidelines 1996.
  15. Sorvillo F, Lieb LE, Nahlen B, et al. Municipal drinking water and cryptosporidiosis among persons with AIDS in Los Angeles County. Epidemiol Infect 1994; 113: 313-320.
  16. Kim LS, Stansell J, Cello JP, et al. Discrepancy between sex- and water-associated risk behaviours for cryptosporidiosis among HIV-infected patients in San Francisco. J Acquir Immune Defic Syndr Hum Retrovirol 1998; 19: 44-49.
  17. Caputo CS, Forbes A, Frost F, et al. Determinants of antibodies to Cryptosporidium infection among gay and bisexual men with HIV infection. Epidemiol Infect 1999; 122: 291-297.
  18. Lemmon JM, McAnulty JM, Bawden-Smith J. Outbreak of cryptosporidiosis linked to an indoor swimming pool. Med J Aust 1996; 165: 613-616.
  19. NSW Department of Health. Infectious diseases -- January-February 1998. NSW Public Health Bulletin 1998; 9: 24.
  20. Lester R. A mixed outbreak of cryptosporidiosis and giardiasis. Update. Quarterly Bull Infect Dis Health Department Victoria 1992; 1: 14-15.
  21. NSW Health. Preventing cryptosporidiosis. A guide for persons with HIV, AIDS and immunosuppressed systems. April 1998.
  22. United States Environmental Protection Agency Office of Water and Centers for Disease Control and Prevention. Safe drinking water. Guidance for people with severely weakened immune systems. <http://www.epa.gov/safewater/crypto.html>. Revised 18 June 1998. Accessed 15 September 1999.
  23. American National Standard/NSF International Standard. Drinking water treatment units -- health effects. ANSI/NSF 53. Ann Arbor MI: NSF International, 1997.
  24. Australian/New Zealand Standard. Water supply -- domestic type water treatment appliances. Performance requirements. AS/NZS 4348. Sydney: Standards Australia, 1995.

Authors' details New South Wales Department of Health, Sydney, NSW.
Paul M Byleveld, PhD, Senior Policy Advisor, Water Unit;
Amanda Hunt, BHB, MPhil(Env Sc), Policy Advisor, Water Unit;
Jeremy M McAnulty, MB BS, MPH, Medical Epidemiologist, Communicable Diseases Surveillance and Control Unit.

Reprints: Dr J M McAnulty, NSW Department of Health, Locked Mail Bag 961, North Sydney, NSW 2059.
jmcanATdoh.health.nsw.gov.au

©MJA 1999
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1: Cryptosporidiosis and HIV/AIDS

During the 1994 cryptosporidiosis outbreak in Nevada, most of the 78 confirmed cases were in HIV-infected adults (61 people, most of whom had CD4+ lymphocyte counts less than 100 cells/µL).7 The remainder of those infected included 11 immunocompetent children, four adults without HIV infection, two HIV-infected children, a renal transplant recipient receiving corticosteroid therapy, and a patient with testicular cancer receiving chemotherapy.

In Australia, there has been a marked decline in the incidence of cryptosporidiosis as the initial AIDS-defining illness since 19949 (Dr G Dore, Lecturer in Epidemiology, National Centre in HIV Epidemiology and Clinical Research, personal communication), and there is little evidence that other classes of immunocompromised persons are currently at greater risk of developing cryptosporidiosis.

In Australia and other countries, the prognosis for those with HIV infection has improved dramatically with the introduction of highly active antiretroviral treatments, which extend the time to development of AIDS and survival time, and arrest the decline in CD4+ lymphocyte counts.9-11 The administration of antiretroviral therapy that includes a protease inhibitor in HIV-positive individuals appears to restore immunity to C. parvum, relieves cryptosporidial diarrhoea and, in some cases, helps eradicate the parasite.12,13 It is possible that, if an outbreak of waterborne cryptosporidiosis were to occur tomorrow, it would have a less severe impact on the HIV-positive community than outbreaks that occurred in the first half of this decade.7,8

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2: Modes of transmission

Cryptosporidium is transmitted by:

  • faecal-oral contact with infected persons (particularly in childcare centres, by not washing hands after going to the toilet, after changing nappies, or from sexual activity that involves exposure to faecal matter);
  • bathing in contaminated water or swimming pools;
  • handling young livestock;
  • contact with animals that have diarrhoea; and
  • consumption of contaminated foods and drinking water (including water supplies when camping or travelling).

A study conducted in Los Angeles concluded that modes of transmission other than drinking water were more important risk factors for the development of cryptosporidiosis in people with AIDS.15 Similarly, a study in persons with HIV in San Francisco revealed that high-risk sexual behaviours were prevalent even among those who were concerned enough about exposures to consume only boiled or bottled water.16 A recent study conducted in persons with HIV in Melbourne suggested that a number of sexual practices, but not CD4+ cell count or tap water consumption, were significant risk factors for prior Cryptosporidium infection.17

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