Cryptosporidium

Introduction by
Professor John R Ashton CBE

Each spring, several hundred people living in the area supplied with water from Thirlmere reservoir in Cumbria become infected with cryptosporidium, which causes gastrointestinal disease. Although usually self-limiting, this disease can be serious especially for those who are immuno compromised, such as people with HIV and AIDS. The privatised water companies claim to be doing everything they can to tackle the problem but here in the North West their expensive improvement programme will take four years to complete. In the meantime people will continue to become ill. We need to ask ourselves whether the companies and public health professionals are doing their best? Is there more that can be done? In the aftermath of the Hatfield rail disaster, the public has started to ask this question of all former public bodies.

Cryptosporidium - the facts

The word 'crypto' means hidden and 'spore' means seed or germ. Cyptosporidium literally means 'hidden germ', and it is a small (4 - 7 micron diameter) single celled protozoan. The form infecting humans as well as a wide range of mammals, including sheep is called Cryptosporidium parvum. It is predominantly a parasite of neonate animals but it can infect humans at any time in their lives although the main burden of disease occurs in children up to 5 years of age. Previous exposure in adult humans appears to result in a degree of partial immunity. Infection, called cryptosporidiosis (often abbreviated to 'crypto') is characterised by severe, watery diarrhoea, with headaches, fever,cramping and nausea. The incubation period for the disease is 4 - 28 days (average of 7 days) and in healthy individuals with a functional immune system, symptoms are usually self-limiting and last for 10 - 15 days. There is no specific treatment. The infectious dose is thought to be around 100 organisms, but some evidence suggests that it could be less than 10. The infection is spread to humans by the faecal -oral route either by person to person or animal to person contact. Known exposure routes include handling nappies from an infected child or caring for an infected person, handling or contact with an infected animal or through contact with contaminated food or water. An infected animal or human excretes millions - possibly billions of potentially infective oocysts per day for a period of approximately 6 -12 days. Exposure to Cryptosporidium in water supplies poses the greatest threat to public health because of the potential to infect large numbers of people very quickly.

Cryptosporidium -as a problem

Although the parasite was first noted in 1907, it was not thought of as a cause of human disease until 1976. The first documented major outbreak was in Texas in the USA in 1984 when 2006 people were infected through sewage contaminated well water. Then in 1993 in Milwaukee, USA over 400,000 people became ill and more than 100 died after drinking lake water that had not been adequately treated. This really put Cryptosporidium in the news and made everyone aware of the public health problems associated with 'Crypto.' Cryptosporidium has several features that make it a difficult germ to eliminate from water supplies. 'Crypto' is spread as oocysts, which are very resistant to chlorine - the usual disinfectant used to purify water. 'Crypto' is very small, and will only be eliminated if all water is passed through an adequate physical barrier such as sand filtration or a membrane less than one micron in diameter, or if the water is boiled.

The situation in the North West

Over 90% of drinking water in the North West comes from surface sources (rivers and reservoirs) and the remainder comes from bore-holes. A large proportion of this surface supply comes from reservoirs in the Lake District, such as the one at Thirlmere in Cumbria. This water passes through a microstrainer, and is then chlorinated and pH adjusted. Microstrainers have a pore diameter of 90 microns and therefore readily allow the passage of cryptosporidium oocysts. When the water treatment plants were built several decades ago, the water was considered to be of such a high quality that further filtration was not required. Thirlmere water is supplied through a hundred mile long aqueduct running from the North West to the South East of the Region; from just north of Grasmere to Manchester. Much of this aqueduct is underground and covered with grazing land. Rain water running off the hills can leak into the aqueduct at various points along its length. There is potential for faecal contamination of the water in the reservoir or the aqueduct from the grazing animals in the area. 'Crypto' outbreaks in the human population in the North West occur in spring time and appear to be associated with the lambing season and heavy rainfall. Wirral, Merseyside and Cheshire receive filtered water from the River Dee and reservoirs in North Wales. The 1999 outbreak of 'Crypto' in the North West provided clear evidence of a link with water supplied from the Thirlmere aqueduct. The figure below shows the difference in infection rates between areas whose population receives drinking water from Wales and the River Dee and the populations that receive water from the Lake District. This is compared to averages for the North West as a whole as well as for England and Wales over the last ten years. Since we do have a high rate of 'Crypto' in the Region, Laboratories in the North West test all stool samples submitted for investigation of gastroenteritis for the presence of 'Crypto' (We are the only region in the Country to engage in such extensive disease surveillance.) But not all Microbiology laboratories routinely notify the Communicable Disease Surveillance Centre of all positive cases immediately, which may slow down their recognition of an outbreak situation.

What is being done

The Government recognised 'Crypto' as public health problem and set up an expert group to examine Cryptosporidium in water supplies. The first two reports came out in 1990 and 1995 under the chairmanship of Sir John Badenoch. The third report - sometimes referred to as the 'Bouchier Report' after the Groups Chairman Professor Ian Bouchier was published in 1999. This group came to the important conclusion that outbreaks do not just 'happen.' There appears to be a strong correlation between outbreak situations and inadequacy of the water treatment process. The report also acknowledged that water is not the only source of 'Crypto' infection in humans. The infection can be acquired from food, swimming pools, contact with farm or domestic animals as well as person to person transmission.

• Fence off critical feeder streams, which pass through fields used by grazing sheep
• Operate bubble mixers in Thirlmere Reservoir to break up the flow of water off the hills so diluting the Cryptosporidium oocysts.
• Remove up to 1000 sheep pregnant with twin lambs from the catchment area around Thirlmere at lambing time. Since 'Cryto' is primarily a disease of neonates, this should reduce the risk of faecal contamination of the reservoir during the lambing season.
• Comply with new national regulations and continuously monitor the water supply for Cryptosporidium oocysts.
• Close down some potentially 'high risk' smaller water supplies, many of which are in a bad state, such as the spring implicated in the Clitheroe outbreak early last year and arrange connection of the properties served to nearby systems where the water has more robust treatment.
• Initiate a programme to substantially improve drinking water treatment, including adequate filtration along the Thirlmere aqueduct. This programme is extensive (around 300 million pounds will be spent) and should when completed substantially reduce the risk of large outbreaks associated with the presence of Cryptosporidium oocysts in drinking water. Unfortunately the work on the last of these treatment plants will not be completed until the
  start of 2005.

Is this enough?

We do not know enough about the relationship between the presence of cryptosporidium cysts in water samples at various points in the system, how contamination occurs, the effect of lambing and the weather to make confident statements about whether or not this will be enough to prevent another water borne outbreak of 'Crypto' next year or even in five years time. This makes it difficult for public health professionals to advise the public about what to do to prevent infection, - particularly in the short term. Considerable controversy exists about the relationship between rainfall, weather and infection and the benefits of asking the public to use bottled water or to boil water after oocysts are found in the water supply. Some say that issuing a boil water alert after oocysts have been found in the water supply is as useless as locking the barn door after the horse has bolted. Maybe there are lessons to be learned from other areas of public health. The recently published Phillips enquiry into BSE acknowledged that nobody in public health or government blatantly put people at risk, but that there were failures in the system and that fears about causing panic delayed appropriate action.

Could these quotes from the executive summary of the report be applied to the current situation with Cryptosporidium?

• At the heart of the BSE story lie questions of how to handle hazard … The Government took measures to address both hazards. They were sensible measures, but they were not always timely nor adequately implemented and enforced
• At times officials showed a lack of rigour in considering how policy should be turned into practice, to the detriment of the efficacy of the measures taken.
• At times bureaucratic processes resulted in unacceptable delay in giving effect to policy.
• The Government was preoccupied with preventing an alarmist over-reaction to BSE because it believed that the risk was remote.
• Gathering of data about the extent of the spreadof BSE was impeded in the first half of 1987 by an embargo … on making information about the new disease public. This should not have occurred.
  

Government eventually enforced precautionary activities to reduce the risk of BSE infection in cattle and the subsequent risk to humans, but the delayed action was at great cost to both the people who already have or possibly still will develop variant CJD as well as to farming. By extrapolating from what we know about 'crypto', and using common sense, we can work out what is likely to reduce the risk of contamination and what level of filtration is required. Surely the BSE crisis has taught us that even if we cannot be sure about the outcomes we must use our professional judgement and take action to protect the public sooner rather than later?

What we know about 'Crypto'

'Crypto' is present throughout the world and ranks as a leading cause of diarrhoreal disease worldwide. Sporadic cases of 'Crypto' undoubtedly occur, and an infected individual is capable of infecting contacts, but when there is a consistently high annual rate of infection; as in some areas of the North West, the most likely cause is contaminated drinking water. Both public and private water sources are at risk of contamination. Until contamination risks are reduced and / or treatment is improved, the public in the North West will remain at risk of further outbreaks of 'Crypto.'

What more can be done?

Information

One of the main conclusions about the BSE crisis according to the Phillips enquiry was that 'The possibility of a risk to humans was not communicated to the public or to those whose job it was to implement and enforce the precautionary measures.' How many people in the North West have heard of Cryptosporidium, let alone know how to protect themselves against it? As public health professionals we should be doing more to publicise the risks throughout the year rather than just reacting when there is an outbreak. North West Water is now continuously monitoring for Cryptosporidium in water supplies, but this information, although on the public register of water quality and thus in the public domain is not easy to access. It is easier to find out about water quality on the other side of the world in Sydney Australia, than it is to find out about the quality of the water coming from our own taps. See this site to see how easily information can be made readily available and accessible to the public; http://www.sydneywater.com.au/. This web site is updated daily and tells us how many
Cryptosporidium oocysts were found in the water today. Since North West Water is sampling for 'crypto' daily, why can we not do this here in the North West? Although we cannot accurately predict when an outbreak will occur, we can inform people about when the high risk season usually occurs. We can also give more information about how people can protect themselves and their families, by following basic hygiene precautions such as strict attention to hand washing after using the lavatory or changing a baby's nappy. We can make sure that everybody knows that the use of boiled, bottled or adequately home filtered water for drinking will reduce the risk of infection. As time progresses a better model will be built up to assist with risk assessment. Surely in this era of open government it is time for North West Water and the public health professionals to extend their partnership working to publicising the fact that tap water cannot be guaranteed safe all the time? However we can honestly estimate the risks, publicise information, answer questions and help people decide what to do to protect themselves.

Our vision for the future

What is our vision for water supplies in the future? What do we need to do to prevent contamination, not just from 'crypto' but from other chemicals and pollutants that threaten our water supplies? Would public health be improved if people used bottled or filtered water for drinking? If we cannot prevent contamination, maybe we should start to question the economics of spending huge sums on purification, when most water is after all used for washing, flushing the lavatory and bathing. Let's have more debate on this. Let's get the information out, and then listen and respond to the public voice

You can view information about water quality in the North West on the United Utilities Website. Click Here

Or directly at North West Water. Click Here

Email:M.Lyons1@livjm.ac.uk