METHODS: We obtained a list of CHSDA counties and ZIP codes for each tribe. Using asthma hospitalization and ED visit data (primary diagnosis ICD-9-CM code 493) from the Minnesota Hospital Association, we calculated age-adjusted rates and 95% confidence intervals by CHSDA and by ZIP code-aggregation for each tribe. We used intercensal county population estimates as denominators for the CHSDA rates and ZIP Code Tabulation Area (ZCTA) estimates from the American Community Survey for the ZIP code-based rates. We also calculated rates for all CHSDA counties, non-CHSDA counties (excluding the Twin Cities metropolitan area), all tribes (based on ZIP codes aggregates), the Twin Cities metro area, and the state.
RESULTS: Both asthma ED and hospitalization rates for CHSDA counties were higher than the non-CHSDA rates and lower than the Twin Cities metro rates. The ZIP code-based asthma ED rate for all tribes was similar to the Twin Cities metro rate and higher than the statewide rate; while the asthma hospitalization rate was not significantly different from the Twin Cities metro rate or the statewide rate. Population estimates by CHSDA and ZIP code aggregate were higher than actual Tribal population counts. For one tribe, the corresponding CHSDA and ZCTA population estimates were 18 and 3 times higher than the actual Tribal population, respectively.
CONCLUSIONS: Rates based on ZIP codes are an improvement on rates by CHSDA counties in terms of representativeness; however, the degree to which these rates truly represent asthma morbidity experienced by American Indians in these areas remains unclear. Future steps include working with Minnesota tribes to calculate rates using internal Tribal claims data. These measures are hugely important for tribes to better understand asthma morbidity among their members as well as the economic costs associated with these potentially preventable outcomes.