PU699 Unit 4 Evidence Synthesis Example

Established, Suggested or Asserted: A Unit 4 Evidence Synthesis on Same-Day Beach Advisories, Organized by the Four Questions a Composite City's Protocol Must Answer and Graded Before It Is Used

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Purdue University Global

PU699: Master of Public Health Capstone

Unit 4 Evidence Synthesis

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[Date]

Port Alder and its protocol are composite; every study, finding and guidance document described is real.

How the Evidence Is Graded

Established: independent studies with different designs agree. Suggested: a few studies point the same way, or one strong study does, but the finding has not been replicated in settings like Port Alder's. Asserted: guidance documents recommend a practice that no study located here has tested. Every source is also tagged with the kind of place it describes, because findings from Chicago's 14 beaches or a single Lake Erie beach may not transfer to a city of four beaches and one creek.

Question One: Do Day-Old Culture Results Misclassify Today's Water?

Answer: yes. Established. Standard culture methods for fecal indicator bacteria need a day or more, so advisories based on them always describe the previous day's water (Wade et al., 2006). The question is whether water changes enough overnight to matter. At Chicago beaches, rapidly changing bacteria concentrations produced both kinds of management error, people swimming in water above the standard and beaches closed when the water was acceptable (Nevers & Whitman, 2011). An intensive study at one Chicago beach, sampling water and sand on consecutive days, showed concentrations tied to conditions that shift daily, including gull activity the day before and the release of bacteria from foreshore sand (Whitman & Nevers, 2003). Port Alder's own figures, 19 of 64 exceedance days with an advisory in place, sit squarely within this pattern. Place tags: urban Lake Michigan beaches, intensive single-beach study.

Question Two: Do Predictive Models Do Better Than Yesterday's Result?

Answer: sometimes, and not everywhere. Suggested. Predictive models estimate today's bacteria level from conditions measured the same morning, such as rainfall, turbidity, wave height and wind. A review of their use found rainfall-based alerts in several communities and multivariable statistical models used operationally for advisories in three areas of the Great Lakes, with rapid laboratory methods still being tested (Francy, 2009). The most careful comparison, at 14 Chicago beaches, found that refining models improved how well they predicted bacteria concentrations at all but one beach, but that models did not always reduce management errors or the overall illness burden. The best results combined models with a locally derived decision threshold (Nevers & Whitman, 2011). The strongest study on predictive models is also the strongest warning about them: they help some beaches and not others, and only a local test can say which kind of beach this is. For Port Alder, this means the protocol cannot adopt a model on the strength of the literature. It must test one on local data first, beach by beach, and keep the current rule where the model does not beat it. Place tags: Great Lakes programs in Ohio and Chicago.

Question Three: Can Rapid Tests Give Same-Day Answers?

Answer: technically yes; whether they protect health better is suggested, not established. A quantitative polymerase chain reaction method measured Enterococcus in freshwater beach samples in three hours or less, with results consistent with membrane filter culture at two Great Lakes beaches (Haugland et al., 2005). In a prospective study of beachgoers at two Great Lakes beaches, Enterococcus measured by this rapid method was associated with gastrointestinal illness after swimming, significantly so at the Lake Michigan beach (Wade et al., 2006). The federal recreational water criteria include a rapid molecular method for Enterococcus that states may use for beach notification (U.S. Environmental Protection Agency [EPA], 2012). What is missing is evidence that a program switching to rapid testing reduced illness among swimmers. Rapid methods also cost more per sample, need trained staff and a laboratory that can run them before mid-morning, and use a different indicator, Enterococcus, from the E. coli Port Alder now measures.

Question Four: Who Is Most Exposed?

Answer: swimmers who swallow water, and especially children. Partly established. Full-contact swimmers were 25 to 50 times more likely than people canoeing, kayaking or fishing to report swallowing a teaspoon or more of water (Dorevitch et al., 2011). The study measured adults and older children at pools and surface waters, so its numbers do not describe young children directly, but the direction is clear and consistent with where advisories matter most: the shallow, crowded water at public beaches in July.

What the Evidence Delivers, and What It Only Suggests

Clearly delivered: the current next-day rule misclassifies water often, and the reasons are well understood. Suggested: a locally tested predictive model may improve advisories at some beaches; rapid tests may let a program post same-day results at one beach if the laboratory can support them. Asserted: guidance that every beach should use a model or a rapid method, which the Chicago comparison contradicts.

Where the Sources Disagree, and Why It Matters Here

The review and the Chicago comparison are not in conflict so much as written from different vantage points. The review describes programs that adopted models and found them useful enough to keep, which is a selected group: programs where models failed are less likely to report it. The Chicago comparison tested several approaches on the same historical data at many beaches at once, which is the stronger design for judging whether models help, and it found that the answer varied by beach. For Port Alder, the second vantage point governs, because the city's four beaches differ in exactly the ways the Chicago work found important. Mill Creek Beach sits beside a creek mouth whose plume depends on rainfall, which predictive variables capture well. Alder Point Beach has a wide sand foreshore and a gull colony, where bacteria levels may track the previous day's birds more than the morning's weather, a source models capture poorly. The synthesis therefore expects the local test to favor a model at the first beach and not at the second, and the protocol should be written so that this outcome is a normal result rather than a failure.

Implications for the Protocol

1. Test a predictive model against the current rule on two seasons of local data, beach by beach, before adopting it anywhere.

2. Use the model only at beaches where it outperforms persistence on both kinds of error.

3. Pilot a rapid method at one beach, if the laboratory can deliver results by 11 a.m., and compare it with the model's calls.

4. Keep the decision threshold under review, as the Chicago work found a local threshold improved outcomes.

5. Measure success as the match between advisories and same-day water, not as fewer illnesses, which the program cannot measure.

Limits of This Synthesis

The literature on this question is small and concentrated in a few Great Lakes cities. Studies were located through two databases and reference lists, and unpublished reports from state beach programs was not searched systematically. Most studies date from before 2015, and newer models may perform differently.

References

Dorevitch, S., Panthi, S., Huang, Y., Li, H., Michalek, A. M., Pratap, P., Wroblewski, M., Liu, L., Scheff, P. A., & Li, A. (2011). Water ingestion during water recreation. Water Research, 45(5), 2020-2028. https://doi.org/10.1016/j.watres.2010.12.006

Francy, D. S. (2009). Use of predictive models and rapid methods to nowcast bacteria levels at coastal beaches. Aquatic Ecosystem Health and Management, 12(2), 177-182. https://doi.org/10.1080/14634980902905767

Haugland, R. A., Siefring, S. C., Wymer, L. J., Brenner, K. P., & Dufour, A. P. (2005). Comparison of Enterococcus measurements in freshwater at two recreational beaches by quantitative polymerase chain reaction and membrane filter culture analysis. Water Research, 39(4), 559-568. https://doi.org/10.1016/j.watres.2004.11.011

Nevers, M. B., & Whitman, R. L. (2011). Efficacy of monitoring and empirical predictive modeling at improving public health protection at Chicago beaches. Water Research, 45(4), 1659-1668. https://doi.org/10.1016/j.watres.2010.12.010

U.S. Environmental Protection Agency. (2012). Recreational water quality criteria (Office of Water 820-F-12-058). U.S. Environmental Protection Agency.

Wade, T. J., Calderon, R. L., Sams, E., Beach, M., Brenner, K. P., Williams, A. H., & Dufour, A. P. (2006). Rapidly measured indicators of recreational water quality are predictive of swimming-associated gastrointestinal illness. Environmental Health Perspectives, 114(1), 24-28. https://doi.org/10.1289/ehp.8273

Whitman, R. L., & Nevers, M. B. (2003). Foreshore sand as a source of Escherichia coli in nearshore water of a Lake Michigan beach. Applied and Environmental Microbiology, 69(9), 5555-5562. https://doi.org/10.1128/AEM.69.9.5555-5562.2003