Aim: We previously reported that incidence rates for chronic lymphocytic leukemia (CLL) among US states are significantly correlated with levels of residential radon (RR). Because these correlations could be influenced by confounding and/or misclassification among large geographic units, we reinvestigated them using smaller geographic units that better reflect exposure and disease at the individual level.
Methods: We examined the relationships between CLL and RR per county in 478 counties with publicly-available data.
Results: After adjustment for ultraviolet radiation, a possible risk factor for CLL, county rates for CLL and RR were significantly correlated among males and females both together and separately (p < 0.0001).
Conclusion: CLL is significantly associated with RR at the county level.
Keywords: chronic lymphocytic leukemia; epidemiology; ionizing radiation; latitude; radon.