MEASURING the risk of infection at work.

The present investigation was prompted by the Northamptonshire Miniature MassRadiography Survey of 1945a-46. One of the findings of this survey, as presented by Smith (1947), was a significantly higher proportion of newly-discovered cases of active pulmonary tuberculosis* among boot and shoe factory workers than among workers in other trades. In July, 1947, the manufacturers asked for an investigation to be carried out, with the object of discovering whether this higher incidence of tuberculosis was the result of working conditions, or whether it was due to factors outside the control of the industry. Since then five related papers have been published. Stewart and Hughes (1949, 1951) describe how an intensive scrutiny of the mass radiography records broke down the total of cases found in boot and shoe factories into a number of homogeneous groups, and, notably, how it was possible to discern an association between cases of chronic tuberculosis and newly-infected cases. The theory that selective recruitment is solely responsible for the high tuberculosis morbidity rate is criticized, and attention drawn to the much higher rates prevalent in large than in small factories. An experiment carried out in Northampton and Leicester by Hirch (1951) shows the level of bacterial contamination of the air in boot and shoe factory workshops to be largely determined by the number of persons present, however close together or far apart they may be. Cairns and Stewart (1951) present a comparative history of the printing and shoe-making trades, to show that, while the living standards enjoyed by shoemakers are not such as would be expected to cause an excess of tuberculosis, there is some plausibility in the theory of a long-wave epidemic in the factory section of the shoe-making community. Webb, Stewart, and Sutherland (1951) discuss the tendency, revealed in a street survey of Northampton, for cases of tuberculosis to occur in adjacent houses. These papers all tend to strengthen the view that infection outside the home is an important factor in the tuberculosis morbidity of boot and shoe workers. Since the original mass radiography survey, fresh material has been gathered which forms the basis of this paper. A further attempt is now made to trace the path of infection in boot and shoe factories, to suggest appropriate measures for