Escherichia coli, or E. coli, consists of a diverse group of bacteria with more than 700 serotypes. These bacteria are found in humans and warm-blooded animals and are an important part of a healthy intestinal tract. Most E. coli are harmless, but a few are pathogenic, meaning they can cause serious illness in humans, including diarrhea, urinary tract infections, respiratory illness, pneumonia, and other illnesses. Pathogenic serotypes are responsible for traveler’s diarrhea and include E. coli O157:H7, the most commonly identified source of E. coli infection during a foodborne outbreak.
Surface waters containing E. coli can cause recreational water illnesses if people swallow or have contact with contaminated water. The most commonly reported symptoms are abdominal pain, diarrhea, nausea, vomiting, and low-grade fever.
Sources of E. coli
Since E. coli originates in human and animal digestive tracts, fecal wastes are the primary source of E. coli contamination in waterbodies. These wastes can enter surface waters from agricultural runoff from fields treated with manure, faulty septic tanks or sewer systems, improper dumping, waste from dogs and livestock, storm events, urban runoff, large concentrations of waterfowl or other wildlife, discharges from boats, and direct human contamination. Pollution of all kinds, including E. coli, is typically higher after rainstorms because the water flowing into streams and lakes travels over lawns, fields, sidewalks, and streets that may contribute sources of fecal contamination.
Once the sources are known, field investigations can help scientists and managers identify problem areas and develop strategies to reduce pollution. Broken sewer lines or faulty septic systems can be difficult to find and repair, but some sources can be corrected through common-sense pollution-reduction practices. For example, livestock manure that reaches tile drains, ditches, or streams from land applications or holding areas near waterways can lead to high levels of E.coli; best management practices can prevent this waste from reaching recreational waters. Individuals can do their part by picking up and disposing of pet waste, keeping septic tanks in good working order, and practicing good hygiene when recreating in surface waters.
Recreational Water Quality Criteria for E. coli
In 2012, the Environmental Protection Agency (EPA) issued two sets of recommended water quality criteria for pathogens and pathogen indicators (such as E. coli) in recreational waters. The 2012 Recreational Water Quality Criteria (RWQC) were based on the results of studies that show the links between illness and fecal contamination in recreational waters. The criteria are designed to protect primary contact recreation, including swimming, bathing, surfing, water skiing, tubing, water play by children, and similar water-contact activities where a high degree of bodily contact with the water, immersion, and ingestion are likely.
Utah uses the Most Probable Number (MPN) test to estimate the concentration of E. coli in a water sample. The presence of a high number of indicator organisms such as E. coli signals a higher probability of pathogens in the water. The threshold of 409 MPN of bacterial density per 100 milliliters (mL) of water relates to a risk factor of 8 illnesses per 1,000 swimmers. As the value of the MPN increases above 409 MPN, the risk of illness if exposed to contaminated waters also increases.
The relationship between the density of E. coli bacteria n samples and the risk of human illness is difficult to quantify. Studies show that the more fecal contamination in the water, the more likely someone will get sick. However, lab results for E. coli below the guidance levels don’t necessarily mean the water is totally safe. The E. coli guidance value is a statistical calculation of when illness is more likely to occur, not a known density at which health effects will occur.