Contact tracing in the late 19th century was mostly related to the large-scale public health crises such as cholera or tuberculosis outbreaks. However, increasingly medical science in the early 20th century realized contact tracing has a positive effect on other forms of infections. Sexually transmitted diseases, which were not well studied prior to the early 20th century, increasingly were treated similar to other infectious disease. In Scotland and UK, during World War I and after, venereal disease became a public health concern. When contact tracing was deployed, it created many problems for those who were seen as passing the infections, mainly women, and the authorities. While initially in the 1920s and 1930s, contact tracing for venereal disease was seen as a way for the authorities to track criminal activity as well as to socially ostracise individuals, public health officials began to change course in the 1930s and 1940s, focusing on conducting detailed interviews with infected individuals and reconstructing sexual history of individuals so that a more clear history of transmission could be developed. This was seen as vital given that the war year in the 1940s could have led to a more rapid spread of disease with the presence of more soldiers in the UK during the period between 1940-1944. Nevertheless, contact tracing focusing on such disease often focused on restricting movements by infected or likely to be infected women, which was seen as the best way to prevent the spread of infection. In the United States, in the late 1930s syphilis was seen as a potential public health threat and the surgeon general Thomas Parran promoted contact tracing as a way to prevent its spread. Similarly, initially the program was difficult to accept socially and was also seen as a way for the authorities to control specific individuals, but by the late 1940s more controlled interviews and use of penicillin, that is penicillin distributed to people likely to get syphilis as well as those who had it, proved to be more successful. Rather than isolating individuals or publicly shaming them, the program simply distributed people in an area who that could likely spread the infection. This helped to rapidly diminish syphilis cases by the 1950s in wide areas of the United States.
Perhaps the most successful example of using contact tracing to diminish the effects of a disease is the example of smallpox, which was mostly eradicated by the 1980s. This was mainly due to efforts of contact tracing, by isolating and treating infected individuals, and then also focus immunization efforts for people nearby. The World Health Organization perhaps established one of the largest contact tracing programs that now focused on the entire world. From the 1950s-1970s, contact tracing was used in developed and developing countries, where teams of volunteers, doctors, and individuals would go and interview people to determine the likely place in which an outbreak was present. This helped to track all major areas of smallpox that eventually led to its near eradication.
==Impact of Contact Tracing==