Professor Mitchell was one of the first in the world to study the epidemiology of H. pylori infection and developed one of the first ELISA assays for the diagnosis of H. pylori infection. Using this she demonstrated that transmission was person to person and showed that infection was mostly contracted in childhood. In 1996 she was a founding organiser of the Western Pacific Helicobacter pylori study group and was convenor of the first meeting in Guangzhou, China and international scientific adviser for subsequent meetings in Malaysia, Indonesia, Australia, Japan and Thailand.