Alexander Jeremiah Orenstein, physician and authority on public health and tropical medicine, grew up in the United States as the son of Jewish immigrant parents. He studied at Jefferson Medical College, Philadelphia, qualifying as Doctor of Medicine (MD) in 1905. That same year he joined the American armed forces and was sent to the Panama Canal, then under construction, where he worked until 1913 under General W.C. Gorgas, a pioneer in the eradication of yellow fever and malaria. During 1913-1914 Orenstein was in German East Africa (now Tanzania) as an advisor on the control of malaria and plague to the German administration and while there helped to direct the redevelopment of Dar es Salaam.
On the advice of General Gorgas he was appointed as chief medical officer to Rand Mines, Ltd in 1914, a post he held until 1969. However, since his American qualifications were not then recognised in South Africa, he was given the title superintendent of sanitation. The next year he went to London and in 1916 qualified as a member of the Royal College of Surgeons (MRCS) of England and a licentiate of the Royal College of Physicians (LRCP) of London. During World War I (1914-1918) he served in the South African Medical Corps from February 1917 to June 1919, attaining the rank of temporary colonel when he became director of medical services in November 1918. That same year he helped to curb a severe outbreak of Spanish influenza in Kimberley, where the emergency services he organised saved many lives.
After the war Orenstein established a department of sanitation (later of health) for the Rand Mines group and began to improve the poor sanitation and health conditions of mine workers, particularly their living conditions and diet. He introduced the appointment of full-time medical officers on the mines, introduced sweeping reforms in the layout of mine hospitals and compounds housing mineworkers, greatly improved hospital facilities, gradually replaced male orderlies with black nurses, introduced training in first aid for mineworkers, and participated in the formation and training of proto-teams. For a long time he had a difference of opinion with Sir Frederick Spencer Lister*, as he was not convinced of the efficacy of pneumonia vaccines produced by the South African Institute for Medical Research. He became an authority on the health of mine workers and his reforms were soon adopted also by other mining companies, with the result that the diseases that had plagued the mining industry were gradually brought under control. His work was later used in planning proper health services at new mines, such as those in the Free State and on the Zambian copper belt, and he was asked to assist with malaria prevention in the Belgian Congo (now the DRC) and the high mortality of Ovambo mineworkers on the diamond fields in Namibia. In 1921 he and F.K. Kleine* visited Northern Rhodesia (now Zambia) in connection with the control of Nagana (sleeping sickness). In 1925 and again in 1928 he was a delegate to the International Labour Conference in Geneva, Switzerland.
Orenstein wrote a book on Mosquito control in Panama; the eradication of yellow fever in Cuba and Panama (New York, 1916), and published, among others, the following papers: 'The problems and principles of malaria prevention' Report of the South African Association for the Advancement of Science, 1915); 'The etiology of scurvy' (1920/1), 'The functions of a sanitary inspector in a modern community' (1920/1) and 'A brief review of some new landmarks in public health' (1922/3) in the Medical Journal of South Africa; 'Fatigue of mine workers' (Transactions of the South African Institution of Engineers, 1921); 'Hookworm infection in the gold mines of the Rand' (with W.O. Fischer, Journal of the Medical Association of South Africa, 1927); 'Hookworm disease' (with W.O. Fischer, 1928) and 'Heat injuries among native miners in the Witwatersrand gold mines' (1929) in the Journal of the Chemical, Metallurgical and Mining Society of South Africa); and 'A review of the hygiene organisation of the Witwatersrand gold mines', delivered at the Third Empire Mining and Metallurgical Congress held at Johannesburg in 1930.
Orenstein was a foundation member and first vice-president of the Mine Medical Officers' Association and served on the Prevention of Accidents Committee of the Chamber of Mines from 1914 to 1956. He became a member of the South African Association for the Advancement of Science in 1915 and of the South African Institute of Mining and Metallurgy in 1916, serving as vice-president of the latter during 1924/5. As the representative of the Witwatersrand Branch of the British Medical Association he was one of the founders of the Associated Scientific and Technical Societies of South Africa in 1920 and served as vice-president during its first year and as president for 1921 and 1922. In 1917 he was a member of the Medical Advisory Committee which participated in negotiations to establish a medical faculty at the South African School of Mines and Technology (from 1922 the University of the Witwatersrand). In 1923 he was appointed by the university as the first lecturer in tropical hygiene and in 1931 was awarded an honorary Doctor of Laws (LLD) degree. Other honours received by him included the gold medals of the Mine Medical Officers' Association, the (British) Institution of Mining and Metallurgy (1958), and the Medical Association of South Africa (1933). He served as president of the latter from 1927 to 1933. For his work in the Belgian Congo he was awarded the Belgian Croix de Chevallier de l'Orde de la Coutonne in 1925. In 1970 he received the Alumni Achievement Award from the Alumni Association of the Jefferson Medical College where he had qualified 65 years earlier. He was an honorary Fellow of the Royal Society of Tropical Medicine and Hygiene and the Royal Society of Medicine.
During World War II (1939-1945) Orenstein served as director-general of medical services in the South African Medical Corps, with the rank of colonel (later major-general). Under his direction the Medical Corps expanded beyond recognition. He served in East Africa and the Middle East, received various medals for distinguished services and was honoured as a Companion of the Order of the Bath (CB) and Commander of the Order of the British Empire (CBE).
In 1956, at the age of 77, Orenstein was appointed as the first director of the Pneumoconiosis Research Unit established by the Council for Scientific and Industrial Research, though he continued as a consultant to Rand Mines. A few years later he served as general secretary to the Pneumoconiosis Conference held at the University of the Witwatersrand in February 1959, and as editor of its Proceedings (1960). He remained active until his death at the age of 92, one of his last contributions being the translation of a Russian research report.
Orenstein had a dominant personality and outstanding organisational abilities. In 1916 he married Kate Bradbury, with whom he had a daughter. After their divorce in 1933 they remarried, but were divorced a second time in 1949.