Department of General Surgery Tangdu Hospital of the Fourth Military Medical University Xi'an 710038 China;
Department of General Surgery Tangdu Hospital of the Fourth Military Medical University Xi'an 710038 China;
Department of Epidemiology the Fourth Military Medical University Xi'an 710032 China;
Department of General Surgery Tangdu Hospital of the Fourth Military Medical University Xi'an 710038 China;
Department of Epidemiology the Fourth Military Medical University Xi'an 710032 China;
Department of Epidemiology the Fourth Military Medical University Xi'an 710032 China;