Introduction:
Expansion of community water fluoridation has stalled in the United States, leaving 115 million Americans without fluoridated drinking water.
Objective:
This study used spatial regression methods to assess contributions of supply-side factors (neighboring counties’ fluoridation coverage) and demand-side factors (health literacy, education, and population density of the local county) in predicting the extent of fluoridation in US counties.
Methods:
For this cross-sectional ecological analysis, data from the 2014 Water Fluoridation Reporting System for all 3,135 US counties were merged with sociodemographic data from the 2014 American Community Survey and county-level estimates of health literacy based on the National Association of Adult Literacy Survey. We employed multilevel geographically weighted autoregressive models to predict fluoridation coverage of each county as a function of fluoridation coverage of neighboring counties and local-county covariates: either health literacy or sociodemographic characteristics. Akaike’s Information Criterion was used to distinguish the better model in terms of explanatory power and parsimony.
Results:
In the best-fit model, an increase from the first to third quartile of neighboring counties’ fluoridation coverage was associated with an increase of 27.76 percentage points (95% confidence limits [CI] = 27.71, 27.81) in a local county’s fluoridation coverage, while an increase from the first to third quartile of local county’s health literacy was associated with an increase of 2.8 percentage points (95% CL = 2.68, 2.89). The results are consistent with a process of emulation, in which counties implement fluoridation based upon their population’s health literacy and the extent of fluoridation practiced in neighboring counties.
Conclusion:
These results suggest that demand for community water fluoridation will increase as health literacy increases within a county. Furthermore, when considering expansion of fluoridation, non-fluoridated communities can benefit from precedents from nearby communities that are fluoridated.