Summary

Contagious diseases have long posed a public health challenge for cities, going back to the ancient world. Diseases traveled over trade routes from one city to another. Cities were also crowded and often dirty, ideal conditions for the transmission of infectious disease. The Europeans who settled North America quickly established cities, especially seaports, and contagious diseases soon followed. By the late 17th century, ports like Boston, New York, and Philadelphia experienced occasional epidemics, especially smallpox and yellow fever, usually introduced from incoming ships. Public health officials tried to prevent contagious diseases from entering the ports, most often by establishing a quarantine. These quarantines were occasionally effective, but more often the disease escaped into the cities. By the 18th century, city officials recognized an association between dirty cities and epidemic diseases. The appearance of a contagious disease usually occasioned a concerted effort to clean streets and remove garbage. These efforts by the early 19th century gave rise to sanitary reform to prevent infectious diseases. Sanitary reform went beyond cleaning streets and removing garbage, to ensuring clean water supplies and effective sewage removal. By the end of the century, sanitary reform had done much to clean the cities and reduce the incidence of contagious disease. In the 20th century, public health programs introduced two new tools to public health: vaccination and antibiotics. First used against smallpox, scientists developed vaccinations against numerous other infectious viral diseases and reduced their incidence substantially. Finally, the development of antibiotics against bacterial infections in the mid-20th century enabled physicians to cure infected individuals. Contagious disease remains a problem—witness AIDS—and public health authorities still rely on quarantine, sanitary reform, vaccination, and antibiotics to keep urban populations healthy.