Density of animal feeding operations, including concentrated animal feeding operations (CAFOs), and cancer incidence: A county-level ecological study across three U.S. states.

BACKGROUND

Animal feeding operations (AFOs) including concentrated animal feeding operations (CAFOs) are significant sources of environmental pollution with potential public health implications. Despite growing concern of environmental health risk, few studies have assessed the associations between exposure to AFOs/CAFOs and cancer incidence across diverse geographic regions and populations.

OBJECTIVE

This study investigates county-level cancer incidence by state in relation to AFO/CAFO exposure in three US states.

METHODS

We analyzed county-level incidence data for all- and site-specific cancers from 2000 to 2021 and AFO/CAFO density for three states (i.e., California, Iowa, and Texas). To address confounding, we applied propensity score matching to compare counties with high AFO/CAFO exposure to control counties. Stratified analyses were conducted by state and cancer type.

RESULTS

Higher exposure to AFO/CAFOs was associated with increased cancer incidence in all three states, although the magnitude and statistical significance of the associations varied by state. Compared to control counties, exposed counties had significantly higher all-cancer incidence rate ratios (IRRs): 1.044 (95% CI 1.040, 1.047) in California, 1.079 (1.066, 1.091) in Iowa, and 1.078 (1.073, 1.084) in Texas. Stratified analyses by cancer type showed higher associations for specific cancers in each state (e.g., bladder cancer in California, colorectal cancer for Iowa, and lung and bronchus cancer in Texas).

CONCLUSION

Our findings suggest a link between higher AFO/CAFO exposure and increased cancer incidence across various US states. Future research using individual-level data, refined exposure assessment, and longitudinal approaches are needed to strengthen the evidence.