Since classical Greece, governments have been aware that diseases spread along trade and travel routes. A population on the move is, almost by definition, a disease on the move, and governments have traditionally acted to prevent the spread of diseases by imposing quarantines and border controls.

During the nineteenth century, governments often created boards of public health and imposed quarantines when epidemics struck a region. These efforts, however, had only a minimal impact on the spread of disease.

In the 1880s, the introduction of bacteriology, the belief that diseases are spread by “germs,” caused a radical shift in the practice of public health. 

Before the discovery of germs, physicians could only diagnose a patient when he or she presented visible symptoms of the disease. The effectiveness of quarantines could be very limited as a result. This was especially true if some patients suffering from contagious diseases were in contact with others during the earliest stages of the disease when signs and symptoms of infection are not yet visible. Now, with bacteriology, physicians could identify a disease in its earliest stages and prevent its spread by isolating the patient.

Trachoma was one of the most common reasons for an immigrant to be denied entry into the United States.  For both the PHS and the US government, trachoma sufferers posed a double threat. First, it was feared that a trachoma sufferer could spark an epidemic once he had been admitted into the United States. Preventing the trachoma sufferer from entering the United States was about protecting the health of those who were already American citizens. A second factor also shaped the PHS’s decision to aggressively search for and detain trachoma sufferers. If a trachoma sufferer were about to become blind, would she be able to support herself? And if not, would she become a charge on the state? The government believed that disabled people would not be able to support themselves.

With this view in mind, they often detained and deported people who had obvious disabilities. This, the government then believed, was about protecting the interests of America’s citizens by ensuring that new Americans would not become a charge on the state. Public health and the exams done at Ellis Island and elsewhere were, first and foremost, about protecting the health and financial well-being of the nation’s current citizens. To a lesser degree, these regulations were also about protecting and caring for the health of potential citizens.