An analysis of hot spots of ESRD in the United States: Potential presence of CKD of unknown origin in the USA?

We hypothesized that high incidence rates of end-stage renal disease (ESRD) in certain counties of the U.S. are partly due to patients with a type of ESRD resembling chronic kidney disease of uncertain etiology (CKDu), which has been observed in Central America and other countries. Using data on 338,126 incident ESRD patients from the United States Renal Data System (USRDS) (2011 - 2013) and the Behavior Risk Factor Surveillance System (BRFSS) Supplement on county-level variables (2006), we describe both patient-level and county-level characteristics in counties with the highest quartile of ESRD incidence rate standardized for age, sex, and race (> 420 cases/million population/year) compared to the rest of the U.S. and two specific "hotspots" of ESRD: the San Joaquin Valley and the Rio Grande Valley. Logistic regression was used to examine characteristics associated with patients who had either missing cause of ESRD or "unknown" listed as the primary cause of ESRD. High incidence rates of ESRD were observed in southern Texas, the Southeast and parts of California (including the San Joaquin valley area), while low rates were seen in the Northwest and the Mountain Regions. The median crude incidence rate of ESRD was 335 (range 0 - 2,341) new cases per million population per year among counties. Significant predictors of missing/unknown primary cause of ESRD included: older age, white or unknown race, non-Hispanic ethnicity, lack of comorbidities at ESRD onset, lower estimated glomerular filtration rate (eGFR) at initiation, and lack of pre-dialysis care. Large areas of the U.S. have very high rates of ESRD incidence. We cannot confirm that CKDu is present in the U.S. based on this preliminary work. This topic therefore requires further investigation, as many of these patients may well be undocumented aliens working as farm laborers and therefore not registered in the USRDS.