As sanitary reform’s engineering leader, London’s Edwin Chadwick, asserted that "all smell is disease", and he proposed that a change in the fundamental structure of sanitation systems was in order to combat increasing urban mortality rates. Chadwick asserted that the problem of epidemics of cholera and typhoid was directly related to urbanization, and he proposed that new, independent sewer systems should be connected to homes. Chadwick supported his proposal with reports from the London Statistical Society which showed dramatic increases in both morbidity and mortality rates since the beginning of urbanization in the early nineteenth century.[22] Though Chadwick proposed reform on the basis of miasma theory, his proposals still contributed to sanitation improvements, such as preventing the reflux of noxious air from sewers back into houses by separate drainage systems in the sanitation designs, which incidentally led to decreased episodes of cholera and thus helped to support the theory.[23]