Geographical distribution of sporadic Creutzfeldt-Jakob disease: analysis by municipality in Apulia between 1993 and 2014

Abstract

Introduction Clustering of sporadic Creutzfeldt-Jakob disease (CJD), a rare fatal neurodegenerative disease with unknown etiology, was investigated in an Italian region. Methods Occurrence of sporadic CJD between 1993 and 2014 was analyzed by municipality in Apulia Region (Italy) using data provided by the Italian Registry of Creutzfeldt-Jakob disease and the Italian Bureau of Statistics. Expected cases by municipality were obtained by internal indirect standardization based on age and gender specific regional incidence rates. We fitted Bayesian hierarchical models with spatially structured and unstructured random components to describe the spatial pattern of the disease and to assess the extent of within and between area clustering. We also evaluated between and within age class (<70; 70+ yrs) clustering by Potthoff-Whittinghill test and search for spatial clusters applying the Kulldorff-Nagarwalla Scan test. Results Between 1993 and 2014, there were 101 incident sporadic CJD cases resident in Apulia (yearly incidence rate: 1.13/1.000.000). 1. The ratio of observed /expected cases ranges by municipality between 0 and 25 – a very implausible value – while the smoothed Bayesian relative risks range between 0.9 to 1.3. There is evidence of between area clustering and two aggregates emerge by this analysis: in the northern, around the city of Foggia; in the middle, in the Valle d’Itria region. 2. No evidence of between or within age class clustering was observed (MonteCarlo p-values within age classes 0.60 and 0.54 respectively). 3. One cluster (MonteCarlo p-value 0.053, 16 cases, 5.3 expected) corresponding to the municipalities of the Valle d’Itria region was detected by the Scan-test analysis. Conclusions Weak evidence of clustering of sporadic CJD was found at a municipality level in an Italian region, but caution is needed in the interpretation of these results.