Supplementary Material for: A Multicentric Prospective Incidence Study of Guillain-Barré Syndrome in Italy. The ITANG Study

<b><i>Background:</i></b> To assess Guillain-Barré syndrome (GBS) incidence we relied on the Italian Network for the study of GBS (ITANG) established in 2010 in 7 Italian regions to analyse the association between influenza vaccination and GBS. <b><i>Methods:</i></b> All individuals aged ≥18 years, presenting with clinical manifestations that suggested GBS according to the universally accepted Asbury's diagnostic criteria (1990) were prospectively notified to a centralised database by ITANG neurologists over the period October 1, 2010-September 30, 2011. Through a telephone survey, 9 trained interviewers followed up the cases to diagnosis and then for 1 year since hospital discharge. Validation of case reporting was performed with the support of administrative data in 5 regions. <b><i>Results:</i></b> We found 365 cases fulfilling the definition for GBS or one of its variants over 19,846,068 population ≥18 years of age, yielding an annual incidence rate of 1.84 per 100,000 (95% CI 1.65-2.03), 2.30 (95% CI 1.99-2.60) in men and 1.41 (95% CI 1.18-1.64) in women. A highly significant peak of incidence was observed in February 2011 as compared to reference month (September 2011, rate ratio 3.3:1, p < 0.01). <b><i>Conclusions:</i></b> In Italy, GBS incidence was among the highest reported in Europe and higher than previously observed in Italian studies.