Methods: Two studies will be presented. For the first, we utilized the US Environmental Protection Agency waterborne disease database, totaling 548 reported outbreaks from 1948-1994, and precipitation data of the National Climatic Data Center. Analyses were at the watershed level, stratified by groundwater or surface water contamination, and by season and hydrologic region. A Monte Carlo version of Fisher's exact test was used to test for statistical significance. In the second study, we conducted time-series analysis to examine stream flow patterns predictive of pfiesteria fishkills along the eastern seaboard of the US. Results: In the first study, fifty-one percent of waterborne disease outbreaks were preceded by precipitation events above the upper 10th percentile and 68% occurred following rainfall months in the upper 20th percentile over a 50 year climate record (p-values 0.001). Outbreaks due to surface water contamination showed strongest association with extreme precipitation during the month of the outbreak, while a two-month lag applied to ground water contamination events. In the second study, Pfiesteria fishkills where most strongly associated with drought conditions 2 months prior to the fishkill. Subsequent heavy run-off episodes following drought conditions increased the probability of a fishkill event.
Discussion. These analyses both shows statistically significant associations between rainfall or stream flows and disease in the US, and are relevant to water managers, coastal fisheries personnel and public health officials in many parts of the world.
Reference: Curriero FC, Patz JA*, Rose JB, Lele S. Analysis of the association between extreme precipitation and waterborne disease outbreaks in the United States, 1948-1994. Am J Public Health 2001 (Aug) 91:1194-99.
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