1. Department of Public Health and Infectious Diseases, Sapienza University of Rome, Rome, Italy.
2. Department of Neurology and Psychiatry, Sapienza University of Rome, Rome, Italy.
3. Multiple Sclerosis Center, Spedali Civili of Brescia, Brescia, Italy.
4. Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland.
5. Clinic of Infectious Diseases, San Raffaele Hospital, Milan, Italy.
6. Department of Pediatrics, Johns Hopkins School of Medicine, Baltimore, Maryland.