The association between extreme precipitation and waterborne disease outbreaks in the United States, 1948-1994

Objectives. Rainfall and runoff have been implicated in site-specific water borne disease outbreaks. Because upward trends in heavy precipitation in th e United States are projected to increase with climate change, this study s ought to quantify the relationship between precipitation and disease outbre aks. Methods. The US Environmental Protection Agency waterborne disease dat abase, totaling 548 reported outbreaks from 1948 through 1994, and precipit ation data of the National Climatic Data Center were used to analyze the re lationship between precipitation and waterborne diseases. Analyses were at the watershed level, stratified by groundwater and surface water contaminat ion and controlled for effects due to season and hydrologic region. A Monte Carlo version of the Fisher exact test was used to test for statistical si gnificance. Results. Fifty-one percent of waterborne disease outbreaks were preceded by precipitation events above the 90th percentile (P =.002), and 68% by event s above the 80th percentile (P=.001). Outbreaks due to surface water contam ination showed the strongest association with extreme precipitation during the month of the outbreak; a 2-month lag applied to groundwater contaminati on events. Conclusions. The statistically significant association found bet ween rainfall and disease in the United States is important for water manag ers, public health officials, and risk assessors of future climate change.