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Frequently Asked Questions
Escherichia coli (E. coli) is one type of bacteria that is commonly found in the intestinal tracts of humans and other warm-blooded animals; it is therefore used as an indicator of fecal contamination of water. Most strains of E. coli are harmless; however, its presence may indicate that pathogens (disease-causing organisms) also are present in the water. 2. What are pathogens, and why is E. coli used to indicate their presence in water? The E. coli bacterium, which is present in the feces of warm-blooded animals, is commonly associated with and is an indicator of several different disease-causing organisms, called pathogens.
Because of its association with pathogens and because it is comparatively easy to grow in the laboratory, E. coli is the basis for Ohio recreational water-quality standards. There are several varieties of pathogenic E. coli and hundreds of varieties of harmless E. coli. One variety of E . coli that is pathogenic has been associated with undercooked ground beef. 3. How are E. coli levels measured? Daily water samples are collected from the beach each morning in sterile bottles. The samples are brought to the laboratory where they are processed for E. coli within 6 hours of collection. The method used to determine levels of E. coli is called membrane filtration. During membrane filtration, a measured amount of water is poured through a filter to trap bacteria onto the filter. The filter is placed on an agar plate and allowed to incubate at a warm temperature overnight. Colonies are counted the next day and recorded as colonies per 100 milliliters. A milliliter is a very small quantity of water—about 0.03 fluid ounces or one-fifth of a teaspoon. 4. What is a water-quality advisory? A Water Quality Advisory is a public notification, typically in the form of a sign posted at the beach, to advise the public that current water quality standards are not acceptable for swimming due to elevated bacteria levels. A Water Quality Advisory remains in effect until another measurement is made that shows that E. coli levels are within acceptable limits. 5. How do beach managers determine when to issue a water quality advisory? There are state standards for E. coli in recreational waters. The state standards are based on those recommended by USEPA and determined by earlier USEPA studies. In USEPA studies, investigators determined that when E. coli levels went up, the number of swimming-associated gastrointestinal illnesses also increased. The Ohio bathing-water standard for E. coli is a single-sample value of 235 colonies per 100 milliliters. If the count for E. coli is equal to or above 235, the beach manager will issue a water-quality advisory. 6. What are the problems with the current method used for issuing beach advisories (based on the previous day’s E. coli level)? Current methods to assess concentrations of E. coli using membrane filtration or other cultural methods take at least 18 hours to complete. During this period, E. coli levels may increase or decrease substantially. A heavy rainfall may cause an increase in E. coli levels overnight. Alternatively, a bright sunny day may cause E. coli levels to fall. So, the beach may be erroneously posted based on measured E. coli levels from the previous day. 7. What is being done to improve the accuracy of the beach advisory system? Scientists are developing and testing tools that can provide beach managers with quick, reliable indicators of recreational water-quality conditions. Predictive models are one means to provide these rapid assessments. Predictive models use easily and quickly measured water-quality surrogates, such as rainfall and wave height, to estimate levels of E. coli or the probability that the bathing-water standard will be exceeded. 8. Is the water safe for swimming? The beach water may appear to be clear and clean, but it doesn’t mean it is safe for swimming. Bacteria cannot be seen in the water; it is therefore important to remember the following guidelines:
9. What illnesses may result from swimming in the water? There is a potential for illness to occur when bacteria levels are unsafe. Gastrointestinal upset, including nausea, vomiting, abdominal cramps, and diarrhea may occur as a result of swallowing contaminated water. There is also a potential for developing upper respiratory infections, in addition to ear and eye infections. Skin infections may also occur if an exposed wound is in contact with contaminated water. 10. Who is most at risk for becoming ill? Children, the elderly, and individuals with weakened immune systems are most at risk for developing illnesses from swimming when bacteria levels are unsafe. 11. What should I do if I became ill after swimming at the beach? If you should become ill, or suspect you became ill, after swimming at the beach, you should notify your doctor and your local health department. Your local health department is interested in tracking illnesses that may have resulted from water-contact activities and will conduct follow-up investigations where necessary. 12. Where does beach pollution come from? Pollution in beach water can be attributed to several factors, the most common of which are sanitary and storm-sewer overflows. In older, urban areas, sanitary and storm-sewer systems were often combined and designed to overflow during heavy rains to prevent basement flooding. It is therefore important not to swim near storm drains or other discharge pipes. Other sources of pollution include sewage-treatment-plant overflows, runoff from lawns and streets, animal wastes (especially waterfowl wastes), malfunctioning home and commercial sewage systems, and boating wastes. 13. How can I help to keep the beach clean? Everyone has a role in keeping the beaches clean, safe, and enjoyable places to visit. The following practices will help to maintain one of our greatest natural resources— Lake Erie.
14. Is there a “pathogen problem” at Ohio beaches? Are people getting sick? There is no true measure of the magnitude of disease associated with recreational water exposures (USEPA, 1999), in Ohio or elsewhere. That is because when people get sick after a weekend at the beach, the cause of illness is unknown. In addition, the illness is not reported unless there was an outbreak among a specific population, like a group of athletes participating in a triathlon. Swimming in polluted water can make you sick (Natural Resources Defense Council, 1998). Epidemiological studies in the United States have consistently found an association between gastrointestinal illness and exposure to contaminated recreational waters; the potential for other types of infections is not completely understood (USEPA, 1999). 15. How would use of the nowcasting system and predictive models differ from the current way of assessing swimming safety? Current methods to assess recreational water quality rely on collecting a sample of water from the beach area, transporting it to a laboratory, and determining numbers of indicator organisms, such as E. coli. It takes as least 18 hours to grow E. coli in the laboratory. Therefore, by the time E. coli results are compiled, beach water-quality conditions may have already changed. By contrast, it takes less than an hour to estimate recreational water quality using the predictive model and transmit results through the nowcasting system. 16. How well do the predictive models work? We tested the model at Huntington using data collected during the recreational season of 2006. The model correctly predicted recreational water quality 80% of the time and worked better than the previous day’s E. coli (the current method used by most beach managers), which correctly predicted recreational water quality 57% of the time. False positive responses for the model were provided 10% of time; that means that the nowcast incorrectly predicted that the standard was exceeded on 6 out of 59 days that the standard was actually NOT exceeded. False negative responses for the model were higher – 42%. That means that the nowcast incorrectly predicted that the standard would NOT be exceeded on 11 out of 26 days that the standard was actually exceeded. Although the false negative rate for the nowcast is higher than we would like, the nowcast still provides more accurate information and better estimates of public health risk than the use of the current method. During 2006, the current method provided false positive and negative responses 30% and 72% of time, respectively. 17. Why was the USGS involved in this research? Water quality and quantity are critical topics in which the USGS has developed expertise over many years. The relatively recent addition of biological science to the agency’s core program creates opportunities to apply science in a variety of new ways. The USGS did not do this research alone. Agencies that cooperated with us on data collection and model development or provided funding were the Ohio Water Development Authority, Northeast Ohio Regional Sewer District, Cuyahoga County Board of Health, and the Ohio Lake Erie Office. 18. Is anyone else doing the same kind of research? Are other prediction tools being investigated? Yes, the USGS and other researchers are working on developing and testing predictive models at coastal beaches. Operational models (those used daily to issue swim advisories or closings) that rely on several explanatory variables (rainfall, wave height, wind direction, etc.) are being used in two other coastal communities in the United States—Project S.A.F.E in northern Indiana and SwimCast in Illinois (Mark Pfister, Lake County Health Department). The USGS Georgia Water Science Center has initiated a bacteria alert program for a recreational river that provides the same type of output as the Lake Erie models—the probability that the standard will be exceeded (Lawrence, 2005). 19. Is it acceptable to use a model to assess recreational water quality? USEPA states that a monitoring program is essential to any beach-management program and recommends that the current E. coli laboratory method be used for assessing ambient waters and for making decisions concerning the protection of human health (USEPA 2002, p. 4-17). However, USEPA also states that modeling tools may be used to supplement, not replace, monitoring. Modeling tools can provide conservative estimates when there is a lag time between sampling the water quality and obtaining results. If models are properly developed and applied, they can be used in making beach advisory or closing decisions (USEPA 2002, p. 4-22).
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We would like to thank Steve Lawrence with the USGS Georgia Water Science Center for help with design suggestions and images. |
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The URL for this page is http://www.ohionowcast.info/ohionowcastfaq.htm For comments or changes regarding this Web page, please contact
Donna Francy |
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Nowcast data are updated daily; last Web page update: July 2, 2008. |
