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BACKGROUND: Cryptosporidiosis and giardiasis are both gastrointestinal diseases acquired through the fecal-oral route, with a primary exposure risk of ingesting contaminated water. Historically, Maine rates for these waterborne diseases have been higher than the national average, but little is known about how the rates are distributed and why they may be elevated. The objective of this project was to geographically analyze disease incidence and explore whether Maine’s water supply infrastructure influences the spatial pattern of these two waterborne diseases.
METHODS: Of the 350 reports of cryptosporidiosis and 1,020 reports of giardia over five years (2010-2014), 301 (86%) and 938 (92%) cases were geocoded, respectively. Suspect, probable, and confirmed cases for each disease were mapped to determine their geographic distribution and variation. The plotted cases were then overlaid on a map layer of wells, intakes, and watersheds for public water supply in Maine. For a subset of cryptosporidiosis (2013-2014) and giardiasis (June-November 2014) cases where risk-exposure data was available, variables such as private-well or community sourced drinking water were also geographically evaluated.
RESULTS: The four counties with the highest incidence for cryptosporidiosis during the 5 year period were Penobscot (66, 22%), Kennebec (42, 14%), Cumberland (33, 11%), and Waldo (26, 9%). The high incidence counties for giardiasis were Cumberland (302, 32%), Androscoggin (79, 8%), Kennebec (72, 8%), and Somerset (70, 7%). In 2013-2014, among 87 cryptosporidiosis cases, 44 (51%) reported private wells as their drinking water source and 26 (30%) cases reported public water. Among 76 giardiasis cases from June-November 2014, 29 (38%) reported private wells and 29 (38%) reported public water.
CONCLUSIONS: Preliminary results highlight areas in the state that may warrant further investigation. These results will help develop future projects to seek and assess other types of GIS layers including agricultural land-use and population census-tract data. Additional analyses are needed to determine whether enhanced surveillance using water-program data would be useful as a routine assessment.