Canadian recreational water quality guidelines - Indicators of fecal contamination: Epidemiological studies for primary contact activities

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• Epidemiological studies
• Definition of gastrointestinal illness and associated risk of illness
• Human sewage impacted beaches
• Non-point source impacted beaches
• Non-swimming primary contact activities
• Rationale for primary contact guidelines
• Guidelines used by other countries/organizations

Epidemiological studies

Over the last several decades, numerous epidemiological studies have been conducted in fresh and marine water recreational environments primarily to investigate an association between E. coli/enterococci fecal indicators and GI. Studies have included recreational water environments impacted by point sources of contamination (that is, the source is identifiable and stationary) and non-point sources of contamination (that is, the sources are diffuse). Most epidemiological studies have been conducted at beaches with known point sources of human fecal contamination. Fewer studies have been conducted on recreational beaches impacted by non-point sources of fecal contamination (see Table 4). Non-point source impacted areas, particularly those with only non-human impacts, may present a lower level of risk to recreational water users at the established guideline levels. However, due to the limited information, additional studies at non-point source impacted beaches are needed to further characterize the potential human health risks at these sites. Studies at sites with both point and non-point sources are important for understanding the variability in the levels of risk to human health and the utility of fecal indicator microorganisms as part of managing recreational water quality. A smaller number of studies have focused on other health endpoints, such as respiratory or skin ailments. The most recent studies have been broadened to include a range of indicators (for example, coliphages, fecal source markers such as HF183) and qPCR detection methods (Sánchez-Nazario et al., 2014; Griffith et al., 2016; Napier et al., 2017). Several reviews of the available epidemiological studies in fresh and marine water recreational environments have also been published (Pruss, 1998; U.S. EPA, 2002; Wade et al., 2003; Fewtrell and Kay, 2015).

The previous edition of this guideline document, published by Health Canada in 2012, reviewed the epidemiological studies published prior to 2009. Since that time, additional epidemiological studies and statistical reanalyses of older datasets have been conducted (Table 4), and the definition used to characterize GI has been expanded (see Definition of gastrointestinal illness). The guideline values for primary contact recreational activities in this document consider all the studies published in Table 4 and balance the potential human health risks and the benefits of recreational water use in terms of physical activity and enjoyment.

Definition of gastrointestinal illness and associated risk of illness

In earlier studies, the association between illness and indicator values was based on a definition of GI that included symptoms of highly credible gastrointestinal illness (HCGI). HCGI was defined as either vomiting, diarrhea with a fever or stomach ache/nausea with a fever (Cabelli, 1983). However, many enteric viruses do not present with fever, and recent studies have shown that enteric viruses are a significant cause of GI among swimmers (Sinclair et al., 2009; Soller et al., 2016). For that reason, in more recent studies a broader definition of GI is used that includes illness with or without fever (see U.S. studies below). This broader definition means more cases of GI would be recorded at a recreational area compared to cases of HCGI. Therefore, it has been necessary to determine the number of cases of GI that is equivalent to the human health risk of HCGI. Recent epidemiological studies in the United States showed that the risk of illness at fresh and marine water beaches was similar at comparable levels of enterococci, and this risk of illness was similar to the freshwater illness rates from previous studies (8 HCGI per 1000 exposed) (U.S. EPA, 2012). Using data on the rates of GI and HCGI in non-swimmers from the available epidemiological studies, it was calculated that a factor of 4.5 must be applied to the rate of HCGI to determine the rate of GI without a fever that corresponds to the same human health risk (Wymer et al., 2013). Applying this factor, the risk of illness in fresh and marine waters at the guideline values in this document are equivalent to 36 GI per 1000 exposed people.

Human sewage impacted beaches

Epidemiological studies have been conducted worldwide at recreational beaches that are impacted by raw and treated human sewage. Table 4 provides an overview of various studies conducted to date and their main conclusions with respect to the link between fecal indicators and GI.

U.S. studies

In the United States, numerous studies have been conducted to support the development of the U.S. EPA's recreational water quality criteria. In the 1980s, two large studies, one in fresh waters and one in marine waters, found statistically significant rates of GI among swimmers and were able to derive regression equations to relate increasing fecal indicator microorganism concentrations to increased risk of HCGI (Cabelli, 1983; Dufour, 1984). For symptoms unrelated to GI, no statistically significant differences were observed (Cabelli, 1983; Dufour, 1984). These studies were used to support the U.S. EPA's 1986 recreational water quality criteria and are the basis for the risk of illness in previous editions of the Health Canada guideline. Between 2003 and 2009, additional epidemiological studies were conducted at freshwater and marine beaches under the National Epidemiologic and Environmental Assessment of Recreational (NEEAR) Water Study (U.S. EPA, 2010; Wade et al., 2006, 2008, 2010). Similar to the studies conducted in the 1980s, the results from the NEEAR studies are applicable to the general human population, including children. Other vulnerable sub-populations (for example, immune-compromised) were not addressed in these studies. The studies monitored sites for enterococci using qPCR and culture-based methods. E. coli data are not available for the study sites. These studies were used to develop the U.S. EPA's 2012 recreational water quality criteria (see Table 6) (U.S. EPA, 2012) and have been used as the basis for the updated values in this document (see Rationale for primary contact guidelines). Two main findings from the NEEAR studies were, first, that enterococci qPCR results had a stronger association with GI than the enterococci culture-based methods, and second, unlike the earlier epidemiological studies, no linear regression equation fit the NEEAR culture-based data. A linear regression equation could be fit to the qPCR enterococci data. Since qPCR detects DNA (as opposed to viability), the enterococci signal may persist longer in the water sources and give a better relationship with risk of illness. The lack of linear regression using culture-based methods may be due to the fact that the wastewater discharges impacting the recreational water quality areas were disinfected, as opposed to the earlier studies, where the wastewater was less treated (U.S. EPA, 2012). However, a cut-point analysis showed that the rate of GI between swimmers and non-swimmers was significantly different when the geometric mean concentration of enterococci exceeded 30 or 35 cfu/100 mL, corresponding to a risk level of 32 or 36 GI (that is, 7 or 8 HCGI) per 1,000 swimmers, respectively. For enterococci qPCR, a regression model was possible using the NEEAR studies. Using the regression model, geometric mean concentrations of 300 and 470 cce of enterococci per 100 mL (corresponding to a risk level of 32 or 36 GI per 1,000 swimmers) provide the level of health protection comparable to that of the culture-based guideline (U.S. EPA, 2012). As E. coli were not measured during these studies, the equivalent thresholds for E. coli concentrations were determined using the regression analysis from Dufour (1984). Geometric mean concentrations of 100 and 126 cfu of E. coli per 100 mL would correspond to the same risk levels of 32 or 36 GI per 1,000 swimmers, respectively. This approach was possible because the rates of illness in the NEEAR studies for both fresh and marine water were similar to the illness rates observed in fresh water in the earlier epidemiological studies. Using the NEEAR study data, the U.S. EPA's 2012 criteria also included accompanying statistical threshold values (STVs) (see Table 6). The STVs approximate the 90th percentile of the distribution of the water quality results and should not be exceeded by more than 10% of the samples used to calculate the associated geometric mean. Using the same water quality distribution, BAVs corresponding to the 75th percentile are included for use in beach management decisions (see Table 6) (U.S. EPA, 2012). These BAVs are the basis for the guideline values in this document (see Rationale for primary contact guidelines, below).

European studies

In Europe, numerous epidemiological studies have also been conducted to investigate links between illness and fecal indicator organisms. Randomized controlled trials were conducted in marine waters in the United Kingdom in the 1990s (Kay et al., 1994; Fleisher et al., 1996). These studies reported significant dose-response relationships between fecal streptococci (considered synonymous with enterococci) and the incidence of both GI and respiratory illness among swimmers. Possible thresholds for an increased risk of gastroenteritis at a concentration of 32 fecal streptococci/100 mL (Kay et al., 1994) and an increased risk of respiratory illness at a concentration of 60 fecal streptococci/100 mL (Fleisher et al., 1996) were reported. At freshwater swimming areas in Germany, Wiedenmann et al. (2006) conducted a randomized controlled prospective cohort study. The authors reported a relationship between the observed rates of illness and measured concentrations of E. coli, enterococci, Clostridium perfringens and somatic coliphages. No-observed-adverse-effect levels (NOAELs) were reported for several definitions of gastroenteritis, ranging from 78 to 180 E. coli/100 mL and from 21 to 24 enterococci/100 mL. The authors proposed guidelines by combining all of the data derived from the different definitions of GI investigated and suggested values of 100 E. coli/100 mL, 25 enterococci/100 mL, 10 somatic coliphages/100 mL and 10 C. perfringens/100 mL. Although the authors propose a value of 100 E. coli/100 mL, it is important to note that the NOAEL reported for GI that most closely fits the criteria of HCGI was 180 E. coli/100 mL and that the definition that most closely fits the broadened GI definition (that is, fever is not required) was 167 E. coli/100 mL. In addition, the quartile and quintile breakdown of the data for the United Kingdom's definition of GI indicated that the rates of swimmer illness compared to those of the control group were not statistically significant until E. coli concentration ranges approached or exceeded 245 E. coli/100 mL and until enterococci concentration ranges approached or exceeded 68 enterococci/100 mL. In a separate study, concentrations of E. coli needed to exceed a geometric mean of 355 E. coli/100 mL before the risk of gastroenteritis was significantly higher in swimmers compared to non-swimmers (Van Asperen et al., 1998).

Another large, randomized-control study in Europe was conducted over 2 summers (2006 and 2007) and investigated both marine beaches (Spain) and freshwater beaches (Hungary) to determine links between health endpoints (GI, respiratory, skin ailments) and the concentration of either E. coli or enterococci (Epibathe report, 2009). Across all study locations, the risk of GI was higher in swimmers than in non-swimmers. Additionally, the risk of becoming ill was higher in marine waters than in fresh waters at similar levels of indicator microorganisms. This may be due to the shorter lifespan of enterococci than the pathogens in marine waters (Epibathe report, 2009). All beaches investigated met the "excellent" water quality criteria as defined in the EU bathing directive (see Table 6). Both the marine and freshwater beaches lacked strong evidence of positive dose-response relationships between E. coli or enterococci and GI. However, the illness levels at both beaches were quite low in comparison to previous studies and therefore, although they enrolled a high number of participants, the study had very low statistical power. To give the study more power, the Epibathe results were combined with previous results from the United Kingdom (marine waters) and Germany (fresh waters) (Kay et al., 1994; Fleisher et al., 1996; Wiedenmann et al., 2006) and a meta-analysis and regression analysis were conducted. Although the meta-analysis was unable to find any dose-response relationship, it did show an increased risk of illness in swimmers versus non-swimmers. The logistic regression, on the other hand, showed an increased risk of GI in marine waters when the enterococci concentrations exceeded 28 cfu/100 mL. No link between microorganism numbers and illness was found in fresh waters with enterococci, but E. coli concentrations exceeding 336 cfu/mL at the freshwater sites were linked with an increased risk of GI in swimmers.

Non-point source impacted beaches

Epidemiological studies

There have been a limited number of epidemiological studies at beaches impacted only by non-point sources of contamination (that is, no human sewage outfalls so minimal risk of human feces) (see Table 4). An early study by Calderon et al. (1991) investigated a freshwater beach with no human contamination sources. Only non-point contamination sources (from a forested watershed) were impacting the beach. No relationship between the risk of GI and the concentrations of E. coli or enterococci was observed. Swimmer illness was associated with high swimmer density and high densities of total staphylococci. Marion et al. (2010) conducted a beach cohort study at a freshwater inland lake in the United States with only non-point source contamination. Municipal wastewater discharges were permitted in tributaries but not directly into the reservoir. E. coli was the only indicator bacteria measured. The results showed that the odds of contracting a GI were 3.2-fold greater for beachgoers entering the water compared to those who did not. The risk of GI was also significantly higher for individuals who consumed food at the beach, potentially related to longer beach exposure times and food-related illnesses. The study also suggested an increased risk of GI or HCGI with E. coli concentrations in the highest 2 quartiles (that is, > 11.3 to 59 cfu/100 mL and > 59 to 1551 cfu/100 mL). Although the increase was not always statistically significant, the trend is suggestive of increased odds of illness. A large study in Florida (Fleisher et al., 2010; Sinigalliano et al., 2010) investigated marine non-point source contaminated beaches. The authors used a prospective randomized exposure study where participants were randomly assigned to water exposure or beach-only exposure. The study reported an increased risk of health impacts in swimmers compared to the beach-only exposure group, but did not find any link between enterococci concentrations and GI. They did, however, report an association between skin ailments and enterococci concentrations.

Quantitative microbial risk assessment studies

Quantitative microbial risk assessment (QMRA) has been used in numerous research studies to better understand the potential health impacts from human pathogens in recreational settings and to investigate the relative risks from different fecal sources. QMRA modelling has generally shown that human and ruminant feces pose the highest risk of human health impacts, while feces from other animals poses a lower risk (Schoen and Ashbolt, 2010; Soller et al., 2010b, 2015). These studies estimate that at similar levels of E. coli or enterococci, the risk to human health from other animals (for example, gulls, pigs, chickens) ranges from 10 to 6,000 times lower than the risks associated with municipal sewage. These data support the recommendation that site-specific alternative recreational criteria be developed by jurisdictional or management authorities for recreational areas at very low risk of human pathogens. In Canada, the Province of Alberta, in its most recent safe beach protocol, has included separate benchmark values for waters with no evidence of human or ruminant fecal contamination (Government of Alberta, 2019). Further information on QMRA, including its use for developing MST targets of health significance, is included in the recreational water quality technical guideline document on Understanding and Managing Risks in Recreational Water Quality (Health Canada, 2023).

Non-swimming primary contact activities

While most epidemiological studies have focused on swimming as the exposure route, there are many other primary contact activities, some of which have undergone limited investigation. In fresh water, a few epidemiological studies have investigated the health effects associated with whitewater canoeing and rafting (Fewtrell et al., 1992; Lee et al., 1997). In marine recreational waters, several epidemiological studies have investigated the health effects of surfing (Harrington et al., 1993; Gammie and Wyn-Jones, 1997; Dwight et al., 2004; Stone et al., 2008; Tseng and Jiang, 2012). The conclusions of these studies are that GI is the most frequently reported, but not the only, adverse health outcome of these types of activities and that factors related to the risk of illness include the water quality and the frequency of immersion and water ingestion.

Rationale for primary contact guidelines

The goal of the primary contact guidelines set out in this document is to protect the health of Canadians during recreational water activities. Numerous studies have shown that individuals have an increased risk of illness when engaging in primary contact recreational water activities in comparison to non-participants. A risk management approach, which includes using the fecal indicator guideline values provided in this document, aims to keep the health risk to a level that is deemed acceptable. The guideline values correspond to a potential risk of 36 GI (equivalent to 8 HCGI) for every 1,000 people engaged in primary contact activities. The 2012 Guidelines for Canadian Recreational Water Quality included an acceptable level of risk of 10 to 20 HCGI (equivalent to 45 to 90 GI) / 1,000 individuals engaged in primary contact activities. The current guideline, therefore, provides a consistent level of public health protection equivalent to the lower range of the acceptable risk levels from the previous guideline.

The guideline values provided in this document for primary contact activities (referred to as BAVs) are adopted from U.S. EPA (2012), based on epidemiological studies conducted in the United States (see Human sewage impacted beaches). The study participants represented the general public, with a greater weighting to children 10 years of age or younger. Children were over-represented in these studies as they may be more susceptible, or have a higher level of exposure (for example, longer time in the water, ingest greater volumes of water), to potential pathogens at recreational water areas. Based on the U.S. EPA analysis, the illness rates in children (aged less than 10) were not significantly different from the general population, so the study results are considered applicable to the general population, including children. These studies reported GI associations with enterococci concentrations for both culture- and PCR-based methods, with the PCR-based methods having a stronger association with the risk of GI. Based on this research, the guideline values in this document now include the use of PCR-based methods for monitoring recreational water quality. The use of PCR-based methods can provide more rapid results for beach management decisions, particularly at high-use beaches where monitoring is conducted daily.

The BAVs shown in Tables 1 and 2 represent the 75th percentile value of the recreational water quality distribution as reported in U.S. EPA (2012). Often, the 90th or 95th percentile values are used for developing benchmark values. However, the 75th percentile value is a more conservative approach as the 75th percentile value is a lower number, meaning beach actions are triggered when fewer fecal indicator organisms are present. Implementing conservative BAVs helps in improving protection of children's health at beaches (U.S. EPA, 2012). Depending on the jurisdictional requirements, BAVs may trigger activities to investigate water quality issues, issue beach notifications, and initiate corrective actions (where applicable). The 75th percentile value for enterococci also aligns with the previous single-sample maximum for this indicator, maintaining a consistent level of public health protection with the 2012 guidelines for enterococci. The BAVs for E. coli are lower than in the 2012 guidelines but are based on the same epidemiological studies as the enterococci values. Further information on the updated guideline values can be found in Development of updated guidelines.

Although the BAVs are recommended for making day-to-day beach management decisions, the overall suitability of an area for recreational use, including an analysis of the long-term trends in water quality, can be assessed using the geometric mean of the sample results. The greater the number of samples included in the calculation of the geometric mean, the more reflective it will be of the water quality. For example, geometric mean concentrations that include samples collected over numerous months (or seasons) can help determine whether the water quality is changing or remaining stable. The geometric mean of the water quality distributions used for the BAVs, which were calculated by the U.S. EPA (2012), are shown in Table 5. By comparing the long-term geometric mean trends with the fecal indicator geometric mean values listed in Table 5, responsible authorities can determine if the water quality is expected to result in the same predicted risk of illness as exposure to water with fecal indicator concentrations corresponding to the BAV provided in Tables 1 and 2. This comparison should not be used for making day-to-day beach decisions, but is recommended for determining a recreational areas overall suitability for recreational activities. Recreational water areas where the geometric mean is consistently higher than the values listed in Table 5 may represent a greater level of risk to human health and may not be suitable for primary contact recreation.

Although this guideline technical document recommends generally applicable BAVs, regulatory authorities can develop site-specific alternative values for areas that are at a low risk for human fecal contamination. QMRA data indicates that the risk of human pathogens varies with the source of the fecal matter, with human and ruminant sources being higher risk (see Quantitative microbial risk assessment studies above). The epidemiological studies used as the basis for the BAVs were conducted in recreational areas with known human fecal sources. In the absence of human fecal sources, the BAVs may represent a risk lower than 36 illnesses per 1,000 individuals (that is, less than 8 HCGI). Therefore, the appropriate regulatory authorities may choose to develop alternative values, to help balance the benefits of engaging in recreational activities with the potential associated health risks associated with these activities.

Guidelines used by other countries/organizations

The guideline values for fecal indicator microorganisms established by international organizations are presented in Table 6. These values are applicable to both fresh and marine waters (unless otherwise indicated).