Cryptosporidiosis outbreak linked to a public water supply

Dr. Phil Jennings

Department of Public Health Tullamore

June 2006

Cryptosporidium Outbreak

• Sporadic cases of cryptosporidium in the previous months

• Two positive cases identified on the same water network by the SAMO

• EHO was contacted and water sampling was initiated on the same day

• Local Authority notified of situation

Cryptosporidium Outbreak (continued)

• Contact with the microbiology lab revealed seven further cases awaiting notification

• Total of thirteen cases notified since the 1st

of April

Outbreak team convened

• SPHM (Chairperson)

• SEHO

• Surveillance Scientist

• Specialist Registrars x 2

• SAMO

• Administrative support

• Lab

Water source

• Spring fed lake

• Population 25,000

• Water chlorinated not filtered

• Pristine water source in the past

• Area surrounding lake predominately farmland

Outbreak control team meeting

• Eight confirmed cases linked to same water supply

• Local authority should be advised of need to issue boil water notice

• Information leaflet prepared for– GPs, Pharmacists, Dentists, Hospital Consultants– Schools, Pre-schools, Food Premises/Pubs– Nursing Homes, Hospitals

Outbreak control team meeting (Continued)

• Communications Officer notified and press statement prepared

• The NDSC and the FSAI were notified

• Meteorological office were contacted to get measurements of rainfall over the previous weeks

Meeting with the Local Authority

• Results of water testing Positive 1 oocyst/10L (domestic tap)

• Boil water notice agreed

• Plan of action three - pronged approach– Epidemiological investigation – Water sampling strategy– Risk assessment

Epidemiological investigation

• Local labs - immediate notification by phone of new cases

• Increased awareness among GPs

• Symptomatic patients advised to submit faecal specimens

• All cases interviewed - questionnaire

• Analysis - Epi-info version 6.4d

Epidemiological investigation (continued)

• 26 confirmed cases on water supply• Age range 11months - 38 years• ~70% < 5 years old• 3 admitted to hospital• 7 unconfirmed cases• Genotyping - Type 2 (Swansea Public Health

Laboratory)• Descriptive epidemiology demonstrated a

link between drinking water and becoming ill

Date of Onset of illness

0

1

2

3

4

5

6

7

04/0

4/02

11/0

4/02

18/0

4/02

25/0

4/02

02/0

5/02

09/0

5/02

16/0

5/02

23/0

5/02

Date of Onset of Illness

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Water sampling strategy

• Co-ordinated between EHO department and the local authority

• Network sample checked for general analysis

• Mixture of grab samples and concentrated samples

• 2nd of May domestic tap - 1/10liters (grab sample)

Results of Water sampling strategy (Continued)

• 2nd of May domestic tap 10 litre grab sample - 1 oocyst/10L

• 4th of May 430 litre continuous filter sample - 1.4 oocysts/10L

• 8th May - 2.4 oocysts/10L

• Water sent for genotyping - Unsuccessful

Risk Assessment

• Water distribution network/source

• Farming Practices identified which could have resulted in contamination of the water source with slurry and farmyard manure - remedial measures undertaken

Risk Assessment (Continued)

• Environmental sampling– Positive for cryptosporidium– Genotyping not successful

• Meteorological data -– Period of dry weather followed by very

heavy rains

Incident control meetings

• Weekly meetings of Incident Control Team

• Criteria developed for recinding of boil water notice

Criteria for rescinding boil water notice

• Enhanced surveillance

• Epidemiological evidence

• Source water quality

• Finished water quality

• Continuing water monitoring

• Ongoing risk assessment

• Action plan for re-issue of boil water notice

Criteria for rescinding boil water notice (continued)

• Programme for cleaning/flushing water mains and reservoirs

• Public notification of recinding of boil water notice

Conclusions

• Using algorithm (UK Public Health Laboratory Service) outbreak strongly associated with water– Oocysts detected in raw/treated water– Descriptive epidemiology demonstrated a link

between drinking water and becoming ill

• Active surveillance and investigation crucial to the detection of this outbreak

Conclusions (Continued)

• This is the first reported outbreak of cryptosporidium associated with a public water supply in the ROI

• Linking infection to drinking water can be difficult as the contamination event may be over by the time the outbreak comes to light

• Cryptosporidia can be difficult to detect in water

Conclusions (Continued)

• Number of oocysts needed to cause infection is small - less than 10

• Laboratories have different policies on testing for cryptosporidium

• Cryptosporidium was not a notifiable disease except as gastro-enteritis in the under twos. Changed in 2004.

Future Water Testing and Treatment

• Temporary filtration system was installed

• Daily monitoring continued - 24 hour continuous filtered sample

• Testing for clostridium perfringens as an indicator organism started in 2004

Directive 98/83/EC on the quality of water intended for human consumption

• If clostridium perfringens is detected, the member state must investigate the supply to ensure that there is no potential danger to human health arising from the presence of pathogenic organisms e.g. Cryptosporidium

• No numerical standard for acceptable cryptosporidium levels is set in this directive

Issues Arising(1)

• Shortage of AMOs curtailing surveillance and follow up

• ?Need for a case control study

• A lot of other Gastrointestinal illnesses e.g.– Rotavirus– SRSV

Issues Arising (2)

• Meeting with local authority– Epidemiological evidence– Positive water sample– ? Response by the Health Board if water

sample negative– ? Response by local authority if water

sample negative

Issues Arising (4)

• Different priorities and pressures– Health Board - Public Health– Local authority - Provision of a water

supply

• Lifting boil water notice– No clear guidelines available

Issues Arising (5)

• Risk assessment consideration of issues e.g.– Likelihood of burns– Public using other water sources e.g.

private wells which may pose greater risks

• Media management

Acceptable Levels of Cryptosporidium in a Water Supply

• Cryptospooridium infection in the population has been reported when levels of cryptosporidium recorded in the water have been low

• No illness has been reported when high levels of cryptosporidium have been detected in a water supply

• Therefore it is difficult to set minimum acceptable levels of cryptosporidium in a water supply

• This highlights the importance of carrying out a risk assessment

Acknowledgements

• Senior Area Medical Officer

• Area Medical Officers

• Environmental Health Officers

• Surveillance Scientist

• Specialist Registrars

• Laboratory Staff

• Administrative staff