Ch 3.3 - Watersports Epidemiological Studies
Canoeist Pathogenic Illness Guide


Chapter 3 - Epidemiological Research (Continued)
3.3 - Watersports Epidemiological Studies
3.3 a) Snorkel Swimming at Bristol Docks. 1981-83
3.3 b) Canoeing in the UK - Various Sites. 1991-92
3.3 c) Canoeing/Rafting at Holme Pierrepont. 1995

Forward to Chapter 4 - Water Treatment and Disinfection

Chapter 3.3 - Watersports Epidemiological Studies

Whilst most epidemiological studies of water related illnesses have looked at bathing, a few studies have looked at other watersports. This section describes three relevant research projects carried out in the UK.

3.3 a) - Snorkel Swimming at Bristol Dock

Philipp R. et al (1985)

Bristol Docks is an enclosed body of water connected to the tidal river Avon and the Severn Estuary. After commercial closure it was developed for recreational use, eg sailing, canoeing, rowing, power-boat racing, sponsored swims, raft racing etc. Total coliform counts and E. Coli counts in the dock were reported to exceed the EC Bathing Water requirements between October and May, and sometimes in the summer months due to surface water run-off after heavy rainfall.

After reports of high illness rates in a snorkel swimming event in 1981, and a post event questionnaire which reported 25% gastrointestinal illness rates after the event in 1982, an epidemiological study was carried out at the event in 1983 to assess the risk. The 87 swimmers who took part were given a questionnaire for completion at the event, and a further questionnaire for return after seven days to report symptoms. Each participant was invited to recruit their own control by co-opting a member of their household, of a similar age, to complete a questionnaire. An additional control group, of visitors to an on-site museum, was recruited to control for non-bathing effects local to the site, such as fast food stalls and air-borne pathogens.

The limited analysis that was carried out in this study showed that 27% (21 out of 77) of the swimmers reported gastrointestinal symptoms, compared to 1 out of 72 for the "family" controls, and 3 out of 86 for the dock visitors.

This symptom rate of 27% is higher than for all of the other studies of bathing water risks. There could be two reasons for this. Firstly the activity, a forty minute snorkel swimming race, involved prolonged, intimate and very vigourous contact with the dock water, and therefore a possible opportunity to ingest high numbers of pathogens into the mouth, digestive system and airways. Secondly, the water samples taken during the event exceeded EC Bathing Water Directive standards (see table 6 below). It is important not give great credence to any single reading or set of readings of indicator organisms, due to the immense variability in spatial and temporal distribution of microorganisms noted in previous reports (especially Fleischer, J. M. 1993). Nevertheless the coliform counts in this case are all significantly above the accepted guide-line values. Streptococcal counts are at acceptable levels, despite streptococci often being proposed as a better indicator of bathing water risk.

Bacterial Counts
Source of Sample Total Coliform E. Coli Faecal Streptococci
Start of Event 24000 2000 14
Halfway Point 91000 900 14
End of Event 80000 2500 22
EEC Guide line / Mandatory standard 500/10000 100/2000 100/-

Table 6. Bristol Dock Water Quality (cfu/100 ml) (Philipp R 1985)

The dock water was tested for viruses, but none were detected by the methods that were available in 1983. Two individuals with diarrhoea provided faecal samples, but no bacterial or viral pathogens could be found in the sample.

3.3 b)Canoeing in the UK - Various Sites. 1991-92

Fewtrell, L. et al (1992, 93, 94)

In the UK in the early 1990 it became clear that although research data was becoming available on which to base public health policy with regard to bathing, especially in marine waters, virtually no data was available concerning a range of other water contact recreational activities, many of which took place on or in fresh water. In 1991/92 Fewtrell and co-workers carried out a series of inter-related studies designed to look at these activities. She looked at white water canoeing at Holme Pierrepont and the river Tryweryn, marathon canoe races on two canals at Gailey and Banbury, and two rowing regattas on river estuaries.

For each study day, two cohorts of volunteers were recruited, one from amongst the competitors in the event, and one from amongst spectators / supporters / family who attended the event but did not go canoeing. Questionnaire and interviews were used to check for non-canoeing risk factors and illness symptoms.

Water sampling took place on all four of the canoeing sites. The river Tryweryn being fed by a high upland, mountain fed reservoir, was as expected very clean. Although Holme Pierrepont was fed by the Trent, which received sewage discharges from a number of sources upstream, the bacterial levels were not particularly high when compared to typical marine bathing waters. Enterovirus concentrations were significantly higher, however. Bacterial levels on the two canals were higher than at Holme Pierrepont, and would have failed EC imperative levels in the Bathing Water Directive. Canal virus counts were not measured.

Faecal Coliform Faecal Streptococci
Holme Pierrepont 286 15
Trywryn 23 14
Banbury 547 37
Gailey 675 61

Table 7. Summary of Indicator bacteria Geometric Mean levels at UK Canoeing sites, Fewtrell, L. 1993

The results from the White Water studies were presented by Fewtrell as three sets of relative risk comparisons. Firstly HPP canoeists were compared with a control group (mainly non-canoeing supporters and spectators). Secondly Tryweryn canoeists were compared with a Trywryn control group. Finally it was possible to compare the groups of HPP and Trywryn canoeists, who had been exposed to different water qualities.

Each comparison consists of two relative risk plots, which compared the relative risk of each of a range of symptoms for the two groups on the day of exposure, and 5-7 days later.

(Note The graphical Relative Risk; plots are reproduced at appendix B of my dissertation, and in the Fewtrell reference, but are too detailed to reproduce on this website. The main findings are outlined here. For more information please see the references).

At Holme Pierrepont there was no statistically significant difference between the canoeists and control group on the day of exposure, which shows that the control group may be valid. At one week after exposure 19 of the symptoms are significantly elevated when compared to spectators. The elevated symptoms include both gastrointestinal and skin/respiratory symptoms.

In a similar study for the Tryweryn, there is very little significant difference between the canoeists and control group apart from the "aching joints" symptom.

The final white water study compared HPP and Tryweryn canoeists, and gives a credible measure of additional morbidity due only to the extra pollution load in the Trent water. This showed a a series of elevated symptom levels including gastrointestinal, skin and eye complaints for HPP canoeists.

Fewtrell reported that:

"minor illnesses of the gastrointestinal tract and upper respiratory system can be intiated by recreation involving a high degree of water contact in fresh waters receiveing sewage effluents. This finding is in agreement with the reported results of the UK national sea bathing research, which is applying similar methods."

Pre and post exposure relative risk plots were also produced for the Banbury Marathon.

Fewtrell reported problems in identifying a suitable control group in the marathon events, as the spectators tended to have a different age, employment and diet profile than the participants. After statistical analysis to discount these effects, it was shown that there is very little quantifiable health risk caused by Marathon canoeing on placid waters. Although the bacterial loading in the canal water was much higher than for Holme Pierrepont, the low contact nature of the marathon when compared to white water paddling presumably accounts for this difference.

3.3 c) - Canoeing/Rafting at Holme Pierrepont. 1995

Lee, J. Dawson, S. et al (1997)

In October 1994 a Cumbrian school teacher took a party of four school children to the Holme Pierrepont slalom course, and three subsequently became ill with gastrointestinal symptoms. Upon investigation the teacher found that other school parties visiting on the same day had high rates of illness. He complained to the Watersports Centre about this risk to schoolchildren, but when not satisfied with the response he started a public campaign to get the course shut down, or at least closed to school parties.

In response to the publicity raised by this event, a Risk Assessment was commissioned to "determine the health consequences of using the slalom course at HPP, measure the size of the risk, assess the relationship between parameters and ill health and identify any factors that lead to a significant risk (Lee, J. 1997).

The research was carried out on 9 days spread throughout the year, and was designed to include a variety of different canoeing and rafting events. The standard technique of on-the-day and follow up questionnaires was used. The study did however include one new feature, in that detailed questions were asked about the actual canoeing activity (see appendix C) in an attempt to determine not just if canoeing per se was a risk factor, but which elements within the overall activity contained most risk. Spectators and canoeists taking part in a sprint regatta on the adjoining regatta course were included to provide control samples.

Water quality was sampled hourly at one point, for bacteria (E. Coli, faecal streptococci and sulphite reducing clostridia), bacteriophages, and viral cultures (enteroviruses). E.Coli and Faecal streptococci levels tended to be within EC Directive levels in the summer, but exceed them in the winter months.

Lee reported:

These findings are commensurate with the findings reported by Fewtrell for white water canoeing, and with a range of other marine and fresh water bathing studies.

In addition, this study was able to look for specific risk factors within the overall activity of a day at Holme Pierrepont.

Diarrhoea, vomiting or other Gastrointestinal symptom with fever Diarrhoea or vomiting
Actvity leading to Symptom Relative Risk Relative Risk
Drinking whilst Wet 2.3 -
Eating whilst Wet - 4.3
Swallowing water on the slalom course 1.7 1.8
Swimming on the slalom course 2.2 1.9
between 1 and 6 previous visits to HPP 1.8 0.9
7 or more previous visits to HPP 0.3 0.3

Table 8. Relative Risk of specific HPP activities (Lee 1997)

Eating or drinking whilst wet (ie before getting changed and washing contaminated water off your hands/lips) was a significant risk factor for gastrointestinal symptoms. Swimming or swallowing water also increased the risk.

The number of previous visits to HPP was an interesting factor. Those who had made many visits to the slalom course had a significantly lower chance of displaying GI symptoms than those who had made fewer visits.

Note by Simon Dawson. There are two published documents relating to this research project at Holme Peirrepont. The Lee 1997 reference is an academic paper written mainly by John Lee (PHLS) and Keith Neal (epidemilogy). There is also the "National Watersports Center Water Quality - Management Report". This 1997 document is a risk assessment study relating to HPP water quality. Copies of the document (or it's up to date successor) should available on request from HPP.

Forward to Chapter 4 | Return to Top of Page