This dissertation examines the multiple factors that influenced the pattern and distribution of infectious disease in Philadelphia between the years 1690 and 1807, and explores the possible reasons for the astonishingly high level of death from disease throughout the city at this time. What emerges from this study is a complex picture of a city undergoing rapid cultural and epidemiological changes. Large-scale immigration supplied a susceptible population group, as international trade, densely packed streets, unsanitary living conditions, and a stagnant and contaminated water supply combined to create ideal circumstances for the proliferation of both pathogens and vectors, setting the stage for the many public health crises that plagued Philadelphia for more than one hundred years.

This study uses an ecological perspective to understand how disease worked in Philadelphia. The idea that disease is virtually always a result of the interplay of the environment, the genetic and physical make-up of the individual, and the agent of disease is one of the most important cause and effect ideas underpinned by epidemiology. This dissertation integrates methods from the health sciences, humanities, and social sciences to demonstrate how disease "emergence" in Philadelphia was a dynamic feature of the interrelationships between people and their socio-cultural and physical environments. Classic epidemiological theory, informed by ecological thinking, is used to revisit the city's reconstructed demographic data, bills of mortality, selected diaries (notably that of Elizabeth Drinker), personal letters, contemporary observations and medical literature.

The emergence and spread of microbial threats was driven by a complex set of factors, the convergence of which lead to consequences of disease much greater than any single factor might have suggested. Although it has been argued that no precondition of disease was more basic than poverty in eighteenth-century Philadelphia, it is shortsighted to assume that impoverishment was a necessary co-factor in the emergence and spread of disease. The urban environment of Philadelphia contained the epidemiological factors necessary for the growth and propagation of a wide variety of infectious agents, while the social, demographic and behavioral characteristics of the people of the city provided the opportunity for "new" diseases to appear.