His interest in the field of tuberculosis control began in 1935 when he became a member of the Division of TB Prevention of the Ontario Department of Health. His primary preoccupation at this time was with traveling chest clinics which were responsible for the conduct of mass surveys on a community basis across the province.
Mr. O’Brien was active in the International Union against Tuberculosis. He helped to host the IUAT meeting in Canada in 1961. At the request of the IUAT, he undertook several world tours to create interest in the voluntary TB movement and has addressed both the IUAT conferences and those of the Eastern Region. In addition, he was part of a traveling seminar which traveled the expanse of the Eastern Region from November 1965 to March 1966, and the criteria set by the seminar are now accepted by the IUAT as the pattern for TB control among the developing countries.