Ullah, Asad, Saif Ullah, Atta Ullah, Muzaffar ud din Sadiq, and Mumtaz Khan. 2011. “FREQUENCY OF HELICOBACTER PYLORI IN PATIENTS PRESENTED WITH PERFORATED PEPTIC ULCER”. Journal of Postgraduate Medical Institute 21 (1). https://www.jpmi.org.pk/index.php/jpmi/article/view/142.