If filth provided European imperialism with a set of legible metaphors about disease and race, then it also gave a newly-forming United States racial principles on which to build a national identity. With institutionalized slavery and a relatively open immigration policy, America, more so than Europe, needed those metaphors to preserve the cultural and moral superiority of particular kind of whiteness (a Teutonic Northern European whiteness). In the late-nineteenth and early-twentieth centuries contagious disease was associated with new immigrant groups who were perceived as harbingers of death.
Nativist groups warned the public of disease that would infect the nation's growing urban areas, rationalizing their prejudice with arguments about public health. In the 1830s, poor Irish were said to bring cholera; at the turn of the century, tuberculosis was dubbed the "tailors' disease" and associated with the Jewish population; Italians for decades were seen as bearers of polio.
To protect against immigrant germs, the United States passed the Immigration Act of 1891, an act that excluded those with "criminal records, polygamist, and prostitutes," as well as those with "loathsome or contagious disease." The Immigration Act made clear that the immigrant carried the filth of both moral degradation and disease. The definition of "loathsome and contagious disease" was flexible and ever-changing, including everything from transmissible disease to insanity, senility, varicose veins, and poor eyesight.
The truth, of course, was that immigrants groups were as healthy as acceptably white Americans. According to contemporary legal scholars, less than three percent of the total number of immigrants seeking entry were rejected for medical reasons; the vast majority of those excluded were Chinese who, unlike their white counterparts, could be rejected for ringworm and "the appearance of mongolism." But yet, despite these facts, white Americans still clamored to close the borders entirely. An 1888 federal report calling for even more immigration restriction warned of the "sewage of vice and crime and physical weakness" that washed ashore from Europe and the "nameless abominations" coming from Asia.