Cryptosporidiosis in North Wales

I am pleased to inform Members that the outbreak of cryptosporidiosis in North Wales was declared over on 30 January 2006.  

The total number of cases of cryptosporidiosis confirmed in the Gwynedd and Anglesey areas since the beginning of the outbreak is 231.  Not all these cases will have been directly linked to the outbreak because a background level of the illness is found all year round. There have been no new cases in the last two weeks.  However the National Public Health Service (NPHS)  would expect a few cases to be diagnosed each month, consistent with background levels normally seen throughout the year. On average three or four cases of cryptosporidiosis are confirmed each month in the Anglesey and Gwynedd areas.

Numbers throughout the UK were high last autumn, but local cases rose rapidly to more than 100 by the end of November, and doubled by mid-December.  Because of the incubation period of the infection – up to two weeks - and because people often have symptoms for several days before visiting the doctor, the effectiveness of the “Boil Water Notice” became apparent from mid December onwards, when the numbers of new cases reported fell sharply.


Boil Water Notice

The Outbreak Control Team advised Dwr Cymru/Welsh Water to lift the “Boil Water Notice” to residents in the Cwellyn water catchment area with effect from Monday 30 January. People can now use tap water for drinking and food preparation without first boiling it, unless they are immuno-compromised and have had specific advice from their doctor.

The decision follows the installation and testing of new equipment at the Cwellyn treatment works.  The reservoir water is now passed through an ultraviolet treatment plant, which will render any cryptosporidium present harmless.  Water companies have been asked by the Drinking Water Inspectorate (DWI) to review their risk assessments in the light of the recent outbreaks of cryptosporidiosis in both England and Wales.  While additional (Ultra Violet) treatment has been installed by Dwr Cymru Welsh Water at the Cwellyn Water Treatment Works, there is no implication at this stage that such levels of treatment will be needed more generally at others of the company’s water treatment works. Such an implication would be premature pending the submission by water companies of the revised risk assessments, asked for by DWI by the end of April, and pending DWI’s investigation of the North Wales cryptosporidium outbreak expected to conclude in April or May.

On 3 January I visited North Wales to meet with the Outbreak Control Team (OCT) and representatives of DWR Cymru/Welsh Water and also visited the reservoir and treatment works. I met senior officials from Dwr Cymru/Welsh Water on 6 February to discuss the public health issues arising from the outbreak.  This was a useful meeting in which Dwr Cymru/Welsh Water explained that their water treatment plant was functioning normally throughout the outbreak and that there were no unusual monitoring results found for Cryptosporidium in this period.

A public health message was highlighted in the meeting in that tap water is subject to more stringent quality standards than bottled water.  The point was made that people with severely impaired immune systems who are more at risk of serious or prolonged illness may not be aware of this fact and may use bottled water considering it a safer substitute and incurring costs in following this practice.  If immuno-compromised patients choose to drink bottled water, this should also be boiled.

The Drinking Water Inspectorate is conducting an investigation into the incident. As with similar incidents affecting drinking water quality, the investigation is proceeding in accordance with the Police and Criminal Evidence Act code of practice as a criminal investigation. It is currently anticipated that the outcome of the DWI investigation will be known towards the end of April/beginning of May when the Assembly Government will be advised of the Inspectorate’s findings, including whether there are grounds for it to initiate either prosecution or enforcement action.        


Investigations

All the available evidence and expert opinion point to Llyn Cwellyn being the probable source of the outbreak. The OCT concluded that there is no alternative explanation.

The Team’s environmental investigations have now identified six possible routes by which the reservoir could have been contaminated with Cryptosporidium hominis, the type found in the majority of people who have been ill.

The Outbreak Control Team has found that there were clinical cases of cryptosporidiosis in the Cwellyn catchment area in early October. One of these cases has been confirmed in the National Public Health Service for Wales’s microbiology laboratories.  A duty to protect confidentiality means that further details cannot be provided.

Detailed investigations have been ongoing since the start of the outbreak.  As well as finding out more about people who have contracted cryptosporidiosis, studies have investigated the climate, geography, geology, and local land use.  Laboratory work on environmental samples is still continuing.



Measures to control the spread of infection

I am advised that people who receive water from the Cwellyn catchment area no longer need to boil the water they use for drinking, food preparation, ice making or teeth brushing. This advice is immediate and applies to all businesses and residents who have previously received written “Boil Water Notice” advice. Although all water consumers are being notified in writing, there is no need to await a letter before using the water again.

People with impaired immune systems, for whom illness may be a greater risk, should continue to follow their doctor’s advice. This will normally include boiling all drinking and bottled water, regardless of source.  Food premises and other business using machines usually supplied by tap water, such as drinks dispensers, have been advised to flush equipment through and change any filters carefully before re-commissioning. Particular care should be taken in the disposal of stagnant water or old filters.  Specialist advice should be obtained directly from individual manufacturers where possible.

The risk of person-to-person spread from those who have become infected by  cryptosporidium still remains. People should continue to be especially thorough with their own hand washing, particularly after using the toilet or before preparing food. Infection spreads very easily between young children.  Adults should therefore supervise toileting and hand washing in this age group whenever possible.



Communications

Dwr Cymru/Welsh Water wrote to all affected customers in the Gwynedd and Anglesey areas on 30 January telling them that the “Boil Water Notice” has been withdrawn.

Environmental Health Departments have also sent letters to managers of food businesses, dental practices, swimming pools, nursing homes and schools informing them that they no longer need to boil tap water and offering further advice on machinery and equipment where relevant.  GPs have also been updated.

The NHS Direct specific helpline established for this outbreak has now closed.  People with any health concerns should contact NHS Direct Wales Tel 0845 4647. The Dwr Cymru/Welsh Water helpline is open 24 hours a day: 0800 052 0130


Outbreak report

The Outbreak Control Team is preparing a full report of the outbreak detailing the action taken and investigations followed. This will include recommendations for any actions the Team considers would help prevent future outbreaks. The report will be available to the public.  When I receive the report, I will consider the recommendations with the Chief Medical Officer to identify any actions that need to be taken by the Assembly Government.


Outbreak in numbers

Number of cases: 231
Faecal samples tested in the NPHS Bangor laboratory::2650

Cryptosporidium isolates tested in the NPHS Cryptosporidium Reference Unit in Swansea: 129

Environmental samples tested in the NPHS Cryptosporidium Reference Unit in Swansea: 56

Staff working on the outbreak: 115

Enquiries received by the NHS Direct helpline: 1500



Appendix

Background

Cryptosporidiosis usually occurs throughout the year.  192 cases were confirmed throughout Wales in 2004 – one case in every 15,000 Welsh residents.  Of these, 36 were in Anglesey and Gwynedd residents. Typically there are greater numbers of cases – peaks – seen in spring time and again at the end of the summer. This normal seasonal variation was seen in Wales during 2004.

In 2005 cases were higher than expected in late summer throughout the whole of the UK, including Wales. More people in Anglesey and Gwynedd contracted the illness than last year, but up to the beginning of November, laboratory reports covering the whole of Wales also showed an overall increase. The C hominis strain of the parasite is more frequently isolated during the autumn peak, and this same strain was found in Gwynedd and Anglesey residents.

Because of the increased illness in the area, Welsh Water began monitoring water supplies daily for Cryptosporidium at the beginning of November and provided mapping of local cases. GPs were also asked to look out for people with symptoms of cryptosporidiosis.

An Incident Management Team of public health experts and Welsh Water staff met on 7 November to discuss these findings and to plan more detailed investigations. Results from this work showed background levels of disease were specifically higher for people living in the Cwellyn catchment area. So on the 24 November the Incident Management Team asked doctors to remind their patients with severely impaired immune systems to boil their tap and bottled water before use. This is because this small group of patients may be at higher risk of serious disease, unlike healthy individuals who may suffer an unpleasant, but self-limiting illness. To ensure everyone knew of the advice a press statement was released and dedicated helplines were set up through NHS Direct.

By 29 November, a questionnaire study had shown an association between diarrhoeal illness due to Cryptosporidium and drinking tap water, even though records revealed the water treatment works for Cwellyn reservoir had been operating normally. Although Cryptosporidium spores were found in the water at Cwellyn, the concentrations remained well within treatment standards.
During the last week of November a steep rise in infections was confirmed in residents supplied with water from the Cwellyn reservoir – a rise not seen in other areas of Wales.  An outbreak was declared and as a precautionary measure the Outbreak Control Team advised Dwr Cymru/Welsh Water to issue a ‘Boil Water Notice’ to residents receiving water from the Cwellyn reservoir on 29 November. At the same time GPs and local health services were reminded of earlier information which they had received concerning the diagnosis, treatment and prevention of cryptosporidiosis.  NHS Direct helpline hours were extended to cope with any increased demand.

The ‘Boil Water Notice’ was extended on 4 January because a continuing risk could not be ruled out.  

The largest waterborne outbreak of cryptosporidium recorded in the UK took place in Torbay, Devon in 1995, involving 575 confirmed cases of illness associated with drinking tap water.  

In Wales waterborne outbreaks are rare. All five Cryptosporidium outbreaks reported since 2000 have been strongly associated with farms and farm animals, in particular visiting open farms. The number of people becoming ill on each occasion has ranged from 2 to 36, and the strain of the parasite normally associated with animal faecal contamination, C parvum, was isolated in laboratory tests.
The last recorded waterborne outbreak of Cryptosporidium in Wales occurred in 1995. A cracked service reservoir in a private water supply at St Athan was linked to diarrhoeal illness in more than 30 people.
 
Drinking water is just one of the routes of transmission of cryptosporidiosis. Some cases are acquired during farm visits, or through swimming in contaminated water including swimming pools, and cases often occur in people returning from abroad. Food borne cryptosporidiosis has occurred but is less common. Person to person spread can cause a local rise in cases, and is particularly common amongst young children.