1. Department of Epidemiological Surveillance and Intervention, Hellenic Centre for Diseases Control and Prevention (HCDCP), Athens, Greece
2. First Department of Pediatrics, University of Athens, “Aghia Sofia” Children's Hospital, Athens, Greece
3. Department of Hygiene and Epidemiology, University of Thessaly, Larissa, Greece
4. Department of Public Health, National School of Public Health, Athens, Greece