A threat to the Irish food and drink industry?
Dr lan Blair - Food Studies Research Centre, University of Ulster at Jordanstown Shore Road, Newtownabbey, Co Antrim BT37 0QB
Introduction
The manufacture of safe and healthy products is of paramount importance to Ireland's food and drink industry. Therefore all producers should be aware of the potential threat posed by Cryptosporidium to safe food production. Accurate and specific information about the occurrence and prevalence of this organism in the Irish food chain is sparse and there has been little published on food or drink related outbreaks of cryptosporidiosis in Ireland1. However, a wealth of information and statistics has accumulated from studies undertaken in other countries that may be of direct relevance to the Irish situation. Cryptosporidium has attracted considerable interest in the UK and the USA as it has been identified as the cause of numerous recent outbreaks of water2 and food borne disease3&4. From these reports it appears that the causative organism is highly prevalent, contamination is widespread, infection is common and control is difficult. For example, cases of cryptosporidiosis have been traced to treated water supplies, although at the time of the outbreaks the water treatment plants met all the current standards for water quality5. Thus, the organism responsible for the disease cryptosporidiosis is unlike any other encountered within the food production industries of developed countries. It is not surprising then that this comparatively recently recognised pathogen is causing considerable concern among those responsible for ensuring and promoting food safety. So what is exactly is Cryptosporidium?
What is Cryptosporidium?
Unlike the majority of the common food safety problems affecting commercial production operations, bacteria do not cause cryptosporidiosis but rather the causative organism is a single celled parasitic protozoan called Cryptosporidium parvum. This organism is closely related to the two other protozoa that are pathogenic to humans, namely Giardia intestinalis (the cause of giardiasis) and Entamoeba histolytica (the cause of amoebic dysentery). All of these protozoa have been linked with contaminated water and food and are generally associated with poor hygiene and low quality water from ineffectively treated or untreated water supplies6. Cryptosporidium parvum has long been recognised as an important pathogen of farm and domestic animals but human cryptosporidiosis was not recognised until 19767. Initially it was considered to be a zoonosis (disease transmitted directly from animals to man) but it is now accepted that transmission may also occur directly from person to person through the faecal-oral route and via inanimate objects and of course through the consumption of contaminated food and drink4.
Cryptosporidium parvum exhibits an extremely complex life cycle most of which occurs in the small intestine of its host. The organism is initially ingested as an oocyst (egg containing cyst), 4-6um in diameter which acts as a reservoir of infection in the environment. Oocysts are highly resistant to most environmental conditions (except dehydration) and this confers great resistance on the organism against the normal range of control mechanisms employed within the food industry. Once ingested the tough protective outer layer of the oocyst is softened by the hosts digestive system and the oocyst splits to release four sporozoites into the small intestine. These sporozoites enter the epithelial cells of the small intestine, to parasitise the cell contents. After the first round of infection is complete the sporozoites undergo asexual reproduction producing more organisms that infect further cells. By this process the organisms can develop into a huge population in a comparatively short time. Following numerous reproductive cycles the parasite population may begin sexual reproduction and produce two types of oocysts - one with thick resistant walls for excretion and another with thin walls that may be excreted or may rupture within a lower portion of the infected host's intestine and the cycle of infection is repeated. None of these cycles of infection and reproduction render Cryptosporidia open to medical intervention and control. The oocyst normal infective dose (ID50), if ingested in water or food, is between 30 and 132 oocysts9 although one report places the minimum infectious dose as low as one oocyst for immunocompromised individuals9. So what are the symptoms of cryptosporidiosis?
What kind of illness does Cryptosporidium cause?
Such large scale invasions of the cells lining the small intestine result in irritation and profuse amounts of watery diarrhoea (up to 20L per day) are produced. These explosive diarrhoeal attacks can result in patients passing of up to 109 oocysts per day8. Additional symptoms of the disease are abdominal cramping, nausea, vomiting, fever and headaches 10 - symptoms typical of most cases of food poisoning. Cryptosporidium parvum can cause illness in anyone who ingests the oocysts but it is most severe in the very young, elderly or the immunocompromised. In healthy adults the disease is self limiting, resolving without treatment within two weeks. Cryptosporidium can cause death in the young and immunocompromised through electrolyte imbalance induced by the diarrhoea. There is no successful drug regimen for treating Cryptosporidium infections and clinical intervention is restricted to monitoring electrolyte levels and maintaining fluid balance. It appears that the body develops an immune response to Cryptosporidium through repeated exposure over time and, thus, the young are at particular risk from this parasite. As a consequence of the development of immunity many adults may be asymptomatically infected and excrete large number of oocysts without any symptoms of the disease4. This has obvious food safety implications if the infected person is a food handler.
How does exposure to Cryptosporidium occur?
The mode of transmission for Cryptosporidium is through the faecal-oral route. Anything that comes into contact with contaminated faecal material, and then ends up in someone's mouth, may cause that individual to develop an infection. Infection may also occur through the water supply and through eating food that has not been cooked properly or which is normally eaten raw. Several reports have highlighted the role of private and public water supplies as a potential source of infection11&12
However, only one study reported the occurrence of Cryptosporidium oocysts in treated water in the UK13. Water may become contaminated through sewage effluent discharges, agricultural runoff and through the practice of spreading treated and untreated animal and human faeces on pastureland. Runoff from such sources may contaminate feeder streams leading to the contamination of watercourses, thus polluting water supplies and food crops subject to irrigation from these sources4. In addition excessive rainfall can overwhelm water treatment plants resulting in contaminated untreated water entering the public supply.
So how can we control Cryptosporidium within the food and drink production industry?
The risk of contamination from raw material can be greatly reduced by careful crop production (segregation of crops from livestock and irrigation with treated water) and selecting raw materials from recognised supplier - applying due diligence principles.
The control of infected food handlers and cross contamination within the work place is best achieved by implementing standard procedures to control faecal-oral contamination:
- workers suffering from diarrhoea (due to any cause) prevented from handling food and relocated away from food handling areas
- scrupulous cleanliness in the work place
- preventative measures such as training and instruction about this pathogen
- strict adherence to the principles of hand hygiene particularly after using the toilet or petting companion animals
The greatest risk to any food business is associated with the water supply used in the production process. Most water supplies are treated before they are delivered to commercial and residential consumers. However, relatively little information exists on the effectiveness of these water treatment processes on the inactivation or removal of Cryptosporidium oocysts. There are two main stages of control that may affect the incidence of Cryptosporidium in potable water - filtration and disinfection.
Filtration - all potable water supplies from a public source should already have been subject to a thorough filtration process. This may take several forms:
- sedimentation - because of their relatively small size and very low density the settling rate of oocysts is extremely low and removal by sedimentation would be insignificant even after long periods of reservoir storage14.
- flocculation - the surface charge of oocysts is low, so clumping with other negatively charged particles should readily occur particularly in the presence of aluminium or iron hydroxide flocs15.
- flotation - this may prove effective when used in conjunction with flocculation16
- rapid filtration - this is likely to be successful if applied after flocculation and sedimentation. Such filtration requires frequent back washing to unclog filters and care is needed to ensure wash water is discarded as it contains very high concentrations of oocysts.
- slow sand filtration - this would seem to offer a highly suitable method for removing oocysts as the top few centimetres support aerobic bacteria that produce a network of extracellular polymers forming a natural biological filter. These filters also require careful maintenance and back washing. Similar precautions should be observed as applied in rapid filtration14.
- membrane filtration - this may be seen as a final finishing process and as such is not often applied to public water supplies. It may, however, be necessary in food and drink production plants to ensure freedom from Cryptosporidium contamination.
Disinfection - there are essentially only three methods of disinfection available that are currently applied to public water supplies and these have not been specifically designed or are not currently applied to remove or destroy Cryptosporidium oocysts.
These are:
- Chlorination - Cryptosporidium oocysts are particularly resistant to chlorination, surviving in undiluted bleach (50g/L NaOCL) for several hours17. Cryptosporidium oocysts are more susceptible to chlorine dioxide but the doses required are inappropriate to water treatment use and it's use may induce the formation of undesirable by-products.
- UV light - to date there have been no reports on the effect of UV wavelength light on Cryptosporidium oocysts. This method is currently suitable only for small volume treatment work.
- Ozonisation - ozone appears to be the most effective disinfectant tested to date18 although the levels required for destruction of Cryptosporidium oocysts are considerably more than those used for normal water treatment purposes. This may prove effective if combined with other filtration and disinfection treatments.
In their comments on the investigation and management of an outbreak of cryptosporidiosis the Badenoch committee18 stated:
"There is a need for high risk premises, such as those used for the preparation of food or ice, to have contingency plans to protect the product should oocysts be found or suspected in the [water] supply. This would be aided by co-operation between the water utilities, local authorities and the owners of the premises at risk to identify the relevant water supply zones by which they are fed"
Therefore, to ensure the water supply used in a commercial operation is of a suitable standard producers should first determine the treatments already applied to the supply before it is delivered. Once in possession of this information producers may then decide to apply further treatments "in-house" to further improve the water supply and increase the margin of safety within the production process and in the final product. There are a number of options open to commercial operations and any decision to upgrade the water treatment facilities "in house" must be a balance between the potential risk to the end product and the additional costs associated with such an upgrade.
The "in-house" water treatment options are:
- heating - while oocysts are resistant to most environmental stress they are destroyed by temperatures exceeding 72.40C for 1 min or 64.2 0C for 5 min4. The resultant water can be certified free of Cryptosporidium oocysts providing the possibility of post processing contamination is prevented. This is not often a viable alternative due to the high energy cost associated with such an option. However if the process incorporates a pasteurisation step as an integral part of the process further heating will be unnecessary. The likelihood of Cryptosporidium oocysts surviving through pasteurisation into the product is insignificant.
- freezing - water to be used in products is frozen at -20 0C for six hours. This method does not guarantee freedom from oocysts and as it is associated with high energy costs it is rarely applied unless as an integral part of the product production process. Additional processes may be necessary to ensure freedom from oocysts in the final product.
- activated charcoal or membrane filtration - this offers the best "in-house" alternative to ensure freedom from Cryptosporidium Oocysts providing it is used to "polish" already filtered and or treated water supplies. Point-of-use or central site water filtration systems of this type can guarantee the removal 99.95% of all particles between 3-4 um and as such should exclude oocysts (4-6 um). Use of such systems with untreated or raw source water cannot be recommended due to he high maintenance and consumable costs incurred17.
Conclusions -so where does this leave the producer?
There can be little doubt that contamination of the food chain by protozoa, such as Cryptosporidium, poses a serious hazard to human health. However, this pathogenic parasite can not be considered as an immediate threat to the entire food and drink production industry. Producers whose products undergo a cooking or pasteurisation processes can be relatively confident in the safety of their products. Such heat treatments will ensure oocyst destruction and will provide a sufficient margin of safety to allow safe food production. This of course is not the case if the heat treatment processes are in some way defective or post-process contamination is a possibility.
Food producers using mains water without further treatment as an integral ingredient of their product or process must evaluate their products and their processing routes to identify and eliminate any potential problems. It is obviously good manufacturing practice to err on the side of safety and given the risk associated with this organism all food and drink manufacturers should perform a risk evaluation on their production facilities and final product range. The impact of this and related organisms as causative agents during recent foodborne disease outbreaks mean there is no room for complacency.
It is the responsibility of the producer to take all reasonable precautions to ensure this product is safe to consume. The manufacturer must ensure they fulfil their public health responsibilities and this may require the installation of "in-house" water treatment facilities. The evaluation of products, processes and procedures is an imperative that no producer can afford to ignore. Such an evaluation should be included in a well organised and maintained HACCP, or related documented quality system, - a feature of well managed production in food and drink companies on this island. While Cryptosporidium may not appear to be a problem to all products or processes - the inclusion of an evaluation specifically for Cryptosporidium within producers HACCP will confirm that this is in fact the case and much more importantly will satisfy customers and consumers of the producers commitment to high quality, and above all, safe food.
References
1 . Corbett-Feeny, G., (1987). Cryptosporidium among children with acute diarrhoea in the west of Ireland, Journal of Infection, 14, pp 79-84.
2. Lisle, J. T., & Rose, J. B., (1995). Cryptosporidium contamination of water in the USA and UK: a mini-review. Journal of Water Supply Research and technology - Aqua, 44, 3, pp 103-117.
3. Casemore D. R, (1990). Special Article: Epidemiological aspects of human cryptosporidiosis. Epidemiology & Infection, 104, pp 1-28.
4. Donnelly, J. K.& Stentiford, E. L.,(1997). The Cryptosporidium problem in water and food supplies. Food Science and technology: Leibensmittel Wissenschaft & Technologie, 30, 2, pp 111- 120.
5. Widmer, 0., Carraway, M. & Tzipori, 5., (1996) Water-borne Cryptosporidium: a perspective from the USA. Parasitology Today, 12, 7, pp 286-290.
6. Lake, R. & Hasell, 5., (1996). Foodborne Cryptosporidium infection. Journal of Environmental Health, 59, 5, pp 39-40.
7 Atherton, E, Newman, C. P. S. & Casemore D. P., (995). An outbreak of waterborne cryptosporidiosis associated with a public water supply in the UK. Epidemiology & Infection 115, pp 123-131.
8. In Cryptosporidium & Cryptosporidiosis, edited by Fayer R. Published by CRC Press Boca Raton 1997. ISBN 0-8493-7695-5
9. Center for Disease Control - CDC, (1997) Cryptosporidium Web site. http://www. cdc.gov/ncidod/publications/brochures/cryptos.htm.
10. Pelehach, L., (1996). When drinking water becomes hazardous to the public's health: The threat of Cryptosporidium. Laboratory Medicine, 27, 1,PP 28-35.
11. LeChevalier, N. W., Norton, W. D. & Lee, R. G., (1991) Occurrence of Giardia and Cryptosporidium in surface water supplies. Applied and Environmental Microbiology, 57, pp 67-73.
12. Rose, J. B., Gerba, C. P. & Jakubowski, W., (1991) Survey of potable water supplies for Cryptosporidium and Giardia. Environmental Science and Technology, 25, pp 1393 - 1399.
13. Smith, H., Grimason, A. Benton, C. & Parker L, (1991) The occurrence of Cryptosporidium spp oocysts in Scottish waters and the development of fluorogenic viability assay for individual Cryptosporidium spp. oocysts. Water Science Technology, 24, pp 169-175.
14. Gregory, J., (1994). Cryptosporidium in water. treatment and monitoring methods. Filtration and Separation, 31, 3, pp 283-289.
15. LeChevalier, N. W., Lee, R. 0. & Moser, R. H, (1990) Evaluation of current treatment practices for the removal of water borne parasites. Internal report, American Water Works Service Co. Inc. Belville, Illinois USA.
16. Edzwald, J. K., Walsh, J. P, Kaminski, 0. 0. & Dunn, H. J., (1992). Flocculation and air requirements for dissolved air flotation. Journal of the American Water Works Association, 84, 3 pp 92- 100.
17. Daniel, P., Gerba, C. P. & Leonard, S., (1994), Cryptosporidium inactivation: an assessment of methods. In: Proceedings of the 1993 Water Quality Technology Conference, Miami, Florida Nov. 7-11. Part 1 Denver: American Water Works Association, pp233-242.
18. Department of the Environment & Department of Health, (1990). Cryptosporidium in water supplies. report of a group of experts: Chaired by Sir John Badenoch. London, HMS0 pp 18-25,117.
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