A hypothesis-generating analysis of the association between extreme weather events and untreated recreational water-associated outbreaks in the United States, 1978-2010 Open Access
Squires, Kelly (2015)
Abstract
Purpose: Acute gastrointestinal illness is the predominant illness in two-thirds of untreated recreational water-associated outbreaks in the United States. Survival and reproduction of waterborne pathogens has been shown to be influenced by both temperature and precipitation. The effects of extreme weather events on waterborne disease is of increasing concern due in part to global climate change and projections of an increase in average temperatures and an increase in severe rainfall events.Studies on a national scale have found positive associations between extreme weather events and waterborne disease outbreaks associated with drinking water. This study aimed to analyze the association between weather events and the incidence of waterborne outbreaks associated with untreated recreational venues in the United States.
Methods: Data on waterborne disease outbreaks were obtained from the Centers for Disease Control and Prevention's Waterborne Disease Outbreak Surveillance System and the National Outbreak Reporting System. Temperature and precipitation data were accessed from the National Oceanic and Atmospheric Administration's National Climatic Data Center. We used a time-stratified 2:1 matched case-crossover design and conditional logistic regression to analyze the relationship between weather and outbreak incidence.
Results: Average minimum temperature in the week preceding an outbreak was significantly associated with outbreak incidence (OR=1.162; 95% CI: 1.017-1.327), but not during other time periods. We also did not find an association between gastrointestinal outbreaks and average maximum temperatures or average precipitation over any time period. We found a stronger effect on E. coli during the 0-28 days preceding an outbreak compared to other pathogens.
Conclusions: The lack of an association in this study between average maximum temperatures and outbreak, as well as average precipitation and outbreaks, could be an indicator that current state and local regulations on beach closures are effective. Subsequent studies on the effects of temperature on gastrointestinal illness should study average minimum temperature as a separate predictor from maximum or average temperatures to further investigate its impact.
Table of Contents
I. Background
Gastrointestinal Illness in the United States. 1
Waterborne Disease in the United States. 1
Recreational Water-Associated Disease. 2
Untreated Recreational Water-Associated Disease. 3
Cryptosporidium. 5
E. coli. 5
Giardia. 6
Shigella. 7
Extreme Weather Events. 8
Effect of Weather on Waterborne Disease. 9
Lag Periods. 12
Case-crossover Analysis. 13
II. Manuscript Introduction. 15
III. Manuscript Methods. 16
Outbreak Data. 16
Weather Data. 17
Case-crossover Analysis. 18
IV. Manuscript Results. 19
Outbreaks. 19
Hazard Periods. 19
Weekly Hazard Periods. 20
V. Manuscript Discussion. 22
VI. Conclusions and Recommendations. 26
VII. References. 29
VIII. Tables and Figures. 39
Table 1. Etiologic Agents involved in Outbreaks of Gastrointestinal Disease in an Untreated Recreational Water Venue, 1978-2010. 39
Table 2. Number of US Counties Reporting Outbreaks of Gastrointestinal Disease in an Untreated Recreational Water Venue 1978-2010. 39
Table 3. Months of the Year in which an Outbreak of Gastrointestinal Disease Occurred in an Untreated Recreational Water Venue, 1978-2010. 40
Table 4. Univariate ORs and 95% CIs for Associations between Weather Event and Reported Outbreaks of Gastrointestinal Illness, 1978-2010. 40
Table 5. Multivariate Adjusted ORs and 95% CIs for Associations between Weather Events and Reported Outbreaks of Gastrointestinal Illness, 1978-2010. 40
Table 6. Univariate ORs and 95% CIs for Associations between Average Minimum Temperature (°C) and Reported Outbreaks of Gastrointestinal Illness, 1978-2010. 41
Table 7. Univariate ORs and 95% CIs for Associations between Average Minimum Temperature and Reported Outbreaks of Gastrointestinal Illness due to E. coli, 1 978-2010. 41
Figure 1. Reported Outbreaks of GI Illness in Untreated Recreational Water Venues, 1978-2010. 42
Figure 2. Odds ratios for the multivariate model including average precipitation over the two-week hazard period (mm), average minimum temperature over the five-week hazard period (°C), and average maximum temperature over the five-week hazard period (°C). 43
Figure 3. Partial Correlation between Five-Week Average Minimum Temperature and Five-Week Average Maximum Temperature. 44
Figure 4. Multivariate Adjusted ORs and 95% CIs for Associations between Average Minimum Temperature (°C, Days 0-28 Preceding Outbreak) and Reported Outbreaks of Gastrointestinal Illness, 1978-2010. 44
Figure 5. Multivariate Adjusted ORs and 95% CIs for Associations between Average Minimum Temperature (°C, Days 0-14 Preceding Outbreak) and Reported Outbreaks of Gastrointestinal Illness, 1978-2010. 44
Figure 6. Univariate OR and 95% CI for Association between Average Minimum Temperature (°C, Days 0-7 Preceding Outbreak) and Reported Outbreaks of Gastrointestinal Illness, 1978-2010. 45
IX. Appendix. 46
Appendix A. US States Reporting Outbreaks of Gastrointestinal Disease in an Untreated Recreational Water Venue, 1978-2010. 46
Appendix B. Univariate ORs and 95% CIs for Associations between Weather Events and Reported Outbreaks of Gastrointestinal Illness, 1978-2010, by Etiology. 47
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