Methods of outbreak investigation in the “ Era of Bacteriology ” 1880 – 1920 355

The advent of bacteriological methods in the later 19th century has been seen, on the examples of America and Germany, to have been followed by a new laboratory-based, contacttracing method of investigating outbreaks of epidemic disease. In Britain, however, this new approach never took firm root, and practising epidemiologists continued to follow an observational and deductive tradition in field investigations, rejecting any primary dependence on bacteriological methods. Alongside this persistent observational practice, there emerged a new statistical approach, based in Pearsonian biometrics, which allied itself with experimental laboratory techniques to develop a more systematic, theoretical trajectory for explaining disease outbreaks in the years after World War I.