[1] Univ Maryland, Sch Med, Dept Epidemiol & Prevent Med, Baltimore, MD 21201 USA
[2] Natl Hepatol & Trop Med Res Inst, Cairo, Egypt
[3] Cairo Univ, Fac Med, Cairo, Egypt
[4] Benha Univ, Fac Med, Banha, Egypt
[5] Mansoura Univ, Fac Med, Mansoura, Egypt
[6] Minya Univ, Fac Med, Minya, Egypt
[7] Menoufia Univ, Fac Med, Menoufia, Egypt
[8] Assiut Univ, Fac Med, Assiut, Egypt