 Number of patients needed: A sample size of N 466 patientsgroup allow 80 power to detect a 30 relative difference in recurrences i.e. from 25 to 17.5 with a chi-square test and a two-sided 5 significance level. Considering an attrition rate around 5 and that the study is a cluster- randomized design, we applied a variance inflation factor equal to 1.5 based on previous studies . 