Original source: Beaches Database, [Public Health Unit]
Distributed by: Public Health Unit
Suggested citation (see Data Citation Notes):
Beaches Database [month, year], Extracted: [date]
- Determine which summary measure is being used for the E.coli criterion to ensure consistency over time.
- Boards of health conduct beach pollution surveys and routine beach surveillance to ensure that public beaches are suitable for bathing. E.coli is an indicator organism that signals the potential presence of viruses and bacteria that may cause disease. E.coli in itself is generally not harmful.
- A pollution survey of a bathing beach area is an on-site investigation into factors and conditions that may influence the quality of bathing beach water.
- Routine beach surveillance consists of collecting a minimum of one sample per week from each sampling site (minimum 5 sites per beach) beginning prior to and continuing over the bathing season.
- A beach is posted if the daily geometric mean of the samples exceeds 100 E.coli per 100-ml. water or if other health hazards have been identified. Examples of other hazards include industrial waste spills, and poor water clarity whereby visibility of submerged swimmers or dangerous objects is insufficient.
- Because of the uneven distribution of bacteria in water, samples are averaged using the geometric mean to reduce the biasing effect of a single high reading. The geometric mean is the antilog of the average of the log of the individual values.
- E.coli levels in beach water are highly influenced by factors such as rainfall, current and wind direction, presence of birds or other animals, as well as management of storm and sanitary sewers.
- Sample collection protocols (number of samples, frequency of sampling) varies by public health unit (PHU) although minimum standards are dictated by the MOHLTC.
- The summary measure used to determine whether E.coli levels have exceeded the criterion can also vary by PHU. Three summary measures are used: the Gmean, Pmean and Run. The Run is commonly used but is not arithmetically very different from the Pmean. The Gmean is the geometric mean of the samples taken on one occasion, usually one day of sampling. The Pmean is the geometric mean of the values from the current and previous days of sampling. The overall Run is the geometric mean of the Gmean (the current day’s samples) and the previous Run. The Run for the first day of samples (Run 1) is the same as the Gmean. The Run for the second sampling day (Run 2) is the same as the Pmean. Run 3 is the geomean of the Gmean and Run 2, and Run 4 is the geomean of the Gmean and Run 3, etc. Thus, the overall Run gives more weight to current samples than previous ones.
- Because of these differences, results are difficult to compare across PHUs. However, this should not affect long term trends within a health unit if the sampling protocol and summary measure used has remained consistent.
- A study at the Durham Region Health Department found that the Run or Pmean appear to give a more reliable indication than the Gmean of whether the beach should be open or posted. The study also found that there was no added benefit of taking 10 samples versus 5 samples per occasion and that the extra work involved in sampling beaches twice versus once per week was not justified.
References and Resources
- Ontario Ministry of Health (1998) Beach Management Protocol, Mandatory Health Programs and Services, Public Health Branch, January 1, 1998.
- Nickol, R. (1992) Fecal Contamination of Recreational Waters, PHERO, 05/22/92, pp. 154-156.
- Bartram J, Rees G (Eds.). Monitoring Bathing Waters. A practical guide to the design and implementation of assessments and monitoring programmes. London: E & FN Spon, 2000; 174-5.
- Holowaty P, Mattes N, Reynolds D. Beach Water Sampling Investigation, PHERO 2001;13(2):8-13.
- Health Canada (1998) Health-Related Indicators for the Great Lakes Basin Population: Numbers 1 to 20. Catalogue No. H46-2/98-219E.