Multiple sclerosis distribution in northern Sardinia. Spatial cluster analysis of prevalence

A heterogeneous geographic distribution of MS has been reported among different ethnic groups,
and also within small communities. Epidemiologic studies conducted over the past two decades using repeated assessments
clearly show that Sardinia is at high risk for MS, with a prevalence of 150 per 100,000 in 1997. Objective: To
present spatial analysis of the disease prevalence to disclose possible “hot” or “cold” spots of disease, further allowing
correlations with risk factors. Methods: A spatial analysis of the whole province of Sassari, in northern Sardinia, at a
microgeographic level (i.e., in the 89 administrative communes and 6 linguistic areas) was conducted. Because of the small
number of cases per commune and to overcome random variability, a hierarchical Bayesian approach was adopted. The
distribution of prevalent cases by commune of residence on December 31, 1997 and from age 5 to 15 years was analyzed.
Results: A clustering pattern was found in the southwestern communes of the province based on geographic distribution
by both prevalence and residence at age 5 to 15 years. A west-to-east gradient also was observed. Conclusions: This study
highlights a hot spot of MS in the southwestern part of Sassari province, bordering with the commune of Macomer, where
MS was once hypothesized as having occurred as an epidemic. Interestingly, these areas of MS clustering comprise the
Common Logudorese linguistic domain. The Catalan area, linguistically and genetically distant from the remaining
Sardinian domains, does not show such high estimates. Because MS is not a single-source infectious disease, this study
may help test the hypothesis that a widely and evenly spread environmental (infectious?) agent may produce disease in
subgroups of genetically more susceptible individuals in areas at higher inbreeding rates, wherein a disease mode of
inheritance could be better investigated.