mitigation measures are not taken early. Consequently, highly coordinated efforts must be put into place early during an outbreak to proactively monitor, detect, and isolate any potentially infectious individuals. If community spread is present, more aggressive measures may be required, up to and including complete cessation of travel in/out of a specific geographic area. History Leper colonies and lazarettos were established as a means of preventing the spread of leprosy and other contagious diseases through social distancing, until transmission was understood and effective treatments invented. 1916 New York City polio epidemic During the 1916 New York City polio epidemic, when there were more than 27,000 cases and more than 6,000 deaths due to polio in the United States, with more than 2,000 deaths in New York City alone, movie theaters were closed, meetings were cancelled, public gatherings were almost non-existent, and children were warned not to drink from water fountains, and told to avoid amusement parks, swimming pools and beaches. Influenza, 1918 to present During the influenza pandemic of 1918, Philadelphia saw its first cases of influenza on 17 September. The city continued with its planned parade and gathering of more than people on 28 September and over the subsequent three days, the city's 31 hospitals became fully occupied. During the week ending 16 October, over people died. Social distancing measures were introduced on 3October, on the orders of St. Louis physician Max C. Starkloff, more than two weeks after the first case. Unlike Philadelphia, St. Louis experienced its first cases of influenza on 5October and the city took two days to implement several social distancing measures, including closing schools, theatres, and other places where people get together. It banned public gatherings, including funerals. The actions slowed the spread of influenza in St. Louis and a spike in cases and deaths, as had happened in Philadelphia, did not occur. The final death rate in St. Louis increased following a second wave of cases, but remained overall less than in other cities. Bootsma and Ferguson analyzed social distancing interventions in sixteen U.S. cities during the 1918 epidemic and found that time-limited interventions reduced total mortality only moderately (perhaps 10–30%), and that the impact was often very limited because the interventions were introduced too late and lifted too early. It was observed that several cities experienced a second epidemic peak after social distancing controls were lifted, because susceptible individuals who had been