setareh mamishi department of pediatrics, pediatrics center of excellence, children's medical center, tehran university of medical sciences, tehran, ir iran pooneh rahimi department of hepatits and aids, pasteur institute of iran, tehran, ir iran; department of hepatits and aids, pasteur institute of iran, 12 farvardin ave, enghelab square, tehran, ir iran. postal code: 1316943551. tel/fax: +98-2166969291 amir sohrabi department of molecular medicine, school of advanced medical technologies, tehran university of medical sciences, tehran, ir iran farah sabuni department of pediatrics, pediatrics center of excellence, children's medical center, tehran university of medical sciences, tehran, ir iran rozita edalat department of virology, pasteur institute of iran, tehran, ir iran ehsan mostafavi department of epidemiology, pasteur institute of iran, tehran, ir iran