Bacteria: enterococcus
From Beachapedia
Introduction
Blue Water Task Force labs and agency-run beach water quality monitoring programs measure enterococcus bacteria levels in recreational waters and compare them to state water quality standards set to protect public health. This resource is meant to provide basic information about enterococcus - what it is, where it comes from, and what it means when this bacteria is present in recreational waters - for Surfrider volunteers and members of the public who are trying to better understand beach water quality monitoring programs and the data they produce.
What is enterococcus?
Enterococcus is a fecal indicator bacteria that naturally occurs in the intestines of warm-blooded animals (mammals and birds). Enterococcus is frequently used to measure recreational water safety across the country and around the world, because it serves as a proxy, or an indicator, for fecal contamination. Epidemiological studies in marine and fresh waters show that enterococcus is one of the best bacterial indicators of public health risk, and this is why state health standards for beaches and recreational waters are based on enterococcus concentrations. All BEACH Act supported, government-run monitoring programs test marine beaches for enterococcus, as do all Surfrider Foundation's Blue Water Task Force labs.
What does it mean when enterococcus is present in recreational waters?
It is important to note that enterococcus bacteria typically do not directly cause human illness, but their presence in water suggests that fecal contamination (or human and animal waste) is present and, therefore, other disease-causing organisms such as viruses, bacteria, and protozoa may also be in the water. It would be very difficult and costly to test for all the possible pathogens that can be found in human or animal feces, thus, health departments measure the levels of enterococcus as a way to assess the risk of people getting sick from exposure to other illness-causing organisms in the water. Swim advisories and beach closures are then issued based on measured enterococcus levels in the water.
Swimming in water contaminated with fecal pollution can lead to illness, with symptoms including gastrointestinal illness, ear infections, skin rashes, and potentially worse. Children, the elderly, and people suffering from autoimmune disorders run a higher risk of getting sick after swimming in polluted and contaminated waters. It’s estimated that around 90 million recreational water-borne illnesses occur nationwide every year. Remember to check local agency water quality data and your local BWTF data before heading to the beach. If you do get sick, please report it to your local state or county health department; local agency contacts can be found here.
How does enterococcus end up in the water?
There are different potential sources of enterococcus and fecal pollution in any given watershed.
Stormwater & Urban Runoff: When it rains, water runs across impermeable surfaces, picking up pollutants from streets, roofs, and yards. These pollutants then run through storm drains, or downhill through streams and rivers, before flowing directly into our beaches. Stormwater and urban runoff is the number one source of beach closures and advisories in the United States, and can make the effects of all sources of bacterial pollution much worse. For instance, wildlife, pet, and agricultural waste is much more likely to enter waterways if the waste is picked up by runoff. Likewise, sewage from cities and towns is more likely to discharge into waterways when heavy rains and flood water enter sewer lines and burden aging wastewater infrastructure pipes, causing sewage overflows. Septic systems and cesspools are also more likely to release or leach untreated wastewater into the groundwater table when surrounding soil is saturated with water.
Sewage: No matter what type of wastewater infrastructure a community or household relies on to treat sewage, failures occur for many different reasons. These failures cause untreated sewage to enter local waterways, and contaminate beaches and other recreational waters. Since enterococcus bacteria occur naturally in human guts, enterococcus counts are often high after a sewage spill has occurred. To learn more about each type of wastewater system, and how they can fail, read the following articles:
Pets and wildlife: When warm-blooded wild animals (i.e. wild pigs, rodents, deer, birds, etc.) defecate near or into a water body, enterococcus counts rise, and risk of recreational water illness in humans increases. To see the impact wildlife can have on fecal bacteria counts, check out this story about how our Northwest Straits chapter cleaned up a popular swimming spot by educating their community about raccoon droppings and water quality.
Similarly, pet feces left on the ground can wash into nearby waterways and contribute to enterococcus counts. Studies show that dogs, in particular, have significantly higher enterococcus concentrations in their feces compared to other animals, such as birds and humans. A comparison of the enterococcus in feces showed that 1 dog fecal event was equivalent to 6,940 bird fecal events in terms of enterococcus counts.
Agriculture: Free range livestock and animal feeding operations produce a large amount of animal waste, which can end up in local waterways if not properly stored or disposed of. Livestock waste can be directly discharged into waterways when illegally dumped, or when cattle are allowed to defecate directly into a waterway. Additionally, runoff can also carry crop fertilizer and livestock waste into waterways and ultimately, nearby beaches.
The methods used by most beach monitoring programs measure the concentrations of enterococcus, but are not able to identify the exact source. Additional testing, usually with more costly and advanced technologies, is required to hone in on what might be causing pollution problems in any given watershed, i.e. sewage, birds, dogs, etc., including potential natural sourcesof enterococcus.
Why sample for enterococcus and not other bacteria?
There are many different pathogens that pollute recreational waters and have the potential to make people sick, yet it would be impossible to develop methods, maintain procedures, and cost-effectively test for individual pathogens. This is why recreational waters are sampled for indicator bacteria, which are surrogates used to measure the potential presence of fecal pathogens, and are also correlated with recreation-borne sickness.
While some agencies may test for E.coli, fecal coliform, or total coliform, studies in marine and fresh waters indicate that enterococcus bacteria are one of the best bacterial indicators of water quality. According to studies conducted by the Environmental Protection Agency (EPA), enterococcus bacteria have a greater correlation with swimming-associated gastrointestinal illness in both marine and fresh waters than other bacterial indicators, and are less likely to "die off" in saltwater. It is important to note that some states, especially in the Great Lakes region, do still monitor freshwater beaches for E. coli.
To learn more about the history of fecal indicator bacteria, and how the state of the science has progressed to measure bacteria types that are more closely related to human illness and public health risk, read this beachapedia article.
Why do Blue Water Task Force labs differ in their state health standards?
The EPA developed recommendations for water quality criteria to be used by states as health standards to protect public health in recreational waters. These criteria are based on the concentration of bacteria measured in a sample of water (either enterococcus or E. coli). Blue Water Task Force labs measure bacteria levels at both marine and freshwater beaches, and compare results to respective state water quality standards.
Example of a water quality standard:
104 colony forming units (CFU) enterococci bacteria / 100 mL water
At beaches, the water quality criteria most widely used to make management decisions, such as issuing swim advisories and opening or closing beaches, is called the Beach Action Value (BAV). BAV’s are mainly determined by the bacteria threshold for a single sample (referred to as a “single sample maximum”) but some states may also use other calculation methods. While BAVs vary state by state, if a water sample exceeds this health standard, either a swim advisory or beach closure is issued depending on state protocols, the severity of the exceedance and/or sources of pollution.
If you are interested in learning more about the health standards set by the EPA, or why your state has different standards than others, please view these blog posts below:
- Beach Water Quality Monitoring Programs in Coastal States
- EPA Updates Recreational Water Quality Criteria
Interested in learning more? Here are some additional resources: