Temporal association of major waterborne disease outbreaks and heavy precipitation events

Background: Long term climate change models predict more frequent heavy precipitations events (PEs). Numerous waterborne disease outbreaks (WBDOs) have been associated with heavy rainfall and runoff. We examine the temporal association between major WBDOs and major PEs (MPEs) in the United States from 1992-2004.

Methods: We constructed a detailed database of WBDOs from CDC MMWR biennial summaries for 1992-2004 and supplemented existing outbreak data with news and public health department reports, thereby allowing improved temporal resolution and more detailed analyses. We obtained daily weather data from NOAA for the continuously operated major weather station nearest each outbreak. We then linked time series of daily precipitation totals for the years 1973-2007 to the appropriate outbreak data and assessed temporal associations with indicator variables for MPE in 1, 2, or 6 months previous to outbreak initiation.

Results: CDC summarized 309 WBDOs in association with untreated recreational water (n=109, 35.3%) and drinking water (n=200, 64.7%), with 9 and 11 major WMDOs, respectively. Among the 20 major WBDOs, 9 (45%) had a single day MPE during the 30 days prior to the outbreak. 3 (15%) had a single week MPE during the 8 weeks prior, and 4 (20%) had a single month M PE during the 6 months prior.

Conclusion: Previous work has suggested that MPEs precede WBDOs more often than expected, but temporal analysis was limited by the detail of available data. Supplementation of existing data to improve this temporal detail will allow for testing of more complex research questions and hypotheses.