Occurrence of cryptosporidium oocysts in leisure pools in the UK, 2017, and modelling of oocyst contamination events

Rachel M. Chalmers*, Lester P. Simmonds, Martin Wood, Megan Luxford, Rob Miller, Rob Johnston

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

Cryptosporidium is a major cause of diarrhoea outbreaks linked to swimming pools, but little is known about the frequency of contamination. The primary aim was to investigate the occurrence and concentration, through sampling and modelling, of Cryptosporidium oocysts in leisure pools. Secondary aims were to compare detections with operational parameters, provide the evidence‐base for guidance, and improve sampling capacity and interpretation for public health investigations. Up to 1000 L pool water was sampled during swim sessions once weekly for 10 weeks from 8th August 2017 at six volunteer pools. Oocysts were detected by microscopy in 12/59 (20%) pool water samples, at least once in each pool; 8/12 (66%) detections were in August when bather loads were highest. At three pools, 1 L filter backwash was sampled weekly and oocysts were detected in 2/29 (7%) samples, following detections in pool water. The probabilities of a bather contaminating the pool ranged from 1 in 1000 to over 1 in 10,000. Monte Carlo analysis showed that when high bather numbers caused contamination on over 70% of days, multiple events per day were more likely than single events. In these generally well‐managed leisure pools, Cryptosporidium risk related to high bather loads. We conclude that public awareness campaigns for bather hygiene, and reminding pool operators of current guidance for managing faecal accidents, should be ahead of peak swim season.

Original languageEnglish
Article number1503
JournalWater (Switzerland)
Volume13
Issue number11
DOIs
Publication statusPublished - 1 Jun 2021

Bibliographical note

Funding Information:
This research was funded by The Pool Water Treatment Advisory Group. The laboratory work was funded by TCS Biosciences, BTF, IDEXX and Latis Scientific, the sampling rigs and their installations were funded by Certikin, Howard Gosling and Total Pool Chemicals Ltd., and Tintometer Limited provided hand?held turbidity meters.

Funding Information:
Funding: This research was funded by The Pool Water Treatment Advisory Group. The laboratory work was funded by TCS Biosciences, BTF, IDEXX and Latis Scientific, the sampling rigs and their installations were funded by Certikin, Howard Gosling and Total Pool Chemicals Ltd., and Tintom‐ eter Limited provided hand‐held turbidity meters.

Publisher Copyright:
© 2021 by the authors. Licensee MDPI, Basel, Switzerland.

Keywords

  • Backwash
  • Cryptosporidium
  • Occurrence
  • Oocyst counts
  • Probability modelling
  • Swimming pool water

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