1. Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran
2. Department of Infectious Diseases and Tropical Medicine, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran
3. Clinical Research Unit, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran
4. Center for Disease Control and Prevention, Mashhad University of Medical Sciences, Mashhad, Iran
5. Department of Statistics, Faculty of Mathematical Sciences, Ferdowsi University of Mashhad, Mashhad, Iran