Trends in coccidioidomycosis incidence in Arizona, 1998–2017: Surveillance changes, weather, and land use Open Access
Khan, Mohammed (Spring 2020)
Abstract
Coccidioidomycosis is an infectious disease caused by inhalation of spores from Coccidioides spp., soil-dwelling fungi endemic in deserts of the Americas. Two-thirds of all cases reported in the United States occur among people living in three counties in central and southern Arizona. Since mandatory laboratory reporting began in 1997, rates of reported disease have increased five-fold. This dissertation examined the impact of surveillance changes on trends in reported coccidioidomycosis and assessed relationships between weather, land use change, and disease incidence.
Reporting and testing changes associated with the Coccidioides enzyme immunoassay at a commercial laboratory caused marked changes in case counts and complicate the interpretation of trends. I estimated bias-adjusted incidence trends in three Arizona counties using probabilistic bias analysis. Bias parameters were estimated from surveillance data and a validation study. Bias-adjusted rates of reported coccidioidomycosis in these three counties were 25% to 47% lower than observed rates. The adjusted average annual percent change in incidence ranged from 5% to 8%.
Weather-related phenomena are thought to influence the growth of Coccidioides and dispersal of spores. I estimated associations between environmental factors (precipitation, air temperature, wind speed, airborne particulate concentration) and incidence and attempted to address methodological issues (changes in surveillance, temporal aggregation of case counts, heterogeneity among reported cases) arising in modeling these relationships. I found positive correlations between one- to two-year lagged winter precipitation, preceding average temperature, and monthly incidence rate. Results were consistent across crude and bias-adjusted analyses and did not change meaningfully using seasonal rates and cases aged 65 years and older.
Residential development in native desert has been hypothesized to increase incidence. I examined the relationship between land development and 2017 census tract incidence. Land development was measured as proportion of structures built after 2010 and remotely sensed development of native desert. Bayesian spatially varying coefficient models were used to estimate associations between land development and incidence. Greater land development was weakly associated (RR 1.04 95%, CrI: 1.01, 1.07) with higher incidence.
Collectively, these studies advance the epidemiology of coccidioidomycosis by more accurately estimating incidence trends and informing efforts by public health agencies to understand coccidioidomycosis risk.
Table of Contents
CHAPTER 1: BACKGROUND 1
CHAPTER 2: LITERATURE REVIEW 28
CHAPTER 3: BIAS-ADJUSTED TRENDS IN REPORTED COCCIDIOIDOMYCOSIS INCIDENCE IN ARIZONA, 1998–2017 50
CHAPTER 4: METHODOLOGICAL ISSUES IN UNDERSTANDING THE RELATIONSHIP BETWEEN WEATHER AND COCCIDIOIDOMYCOSIS INCIDENCE IN ARIZONA 72
CHAPTER 5: LAND DEVELOPMENT AND REPORTED COCCIDIOIDOMYCOSIS INCIDENCE IN CENTRAL AND SOUTHERN ARIZONA 110
CHAPTER 6: CONCLUSIONS AND FUTURE DIRECTIONS 128
REFERENCES 137
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