Today they are hired primarily by the U.S. Centers for Disease Control and Prevention (CDC) and serve in many public health programs.
This type of worker is unique in public health, because they begin their service at the entry level of public health doing what is known as "field work" or "contact epidemiology" which refers to the interviewing and locating of people who have been exposed to an infectious disease so as to offer them treatment and to reduce the epidemic.
[4][7] Following both World Wars (I and II), syphilis was seeded in the population because the public health infrastructure was not funded well enough to respond to cases of the disease.
PHAs are part of a deployable team that can be credited with the eradication of smallpox, the identification of new strains of disease, and the halting of epidemics.
[10] PHAs have been called to respond to outbreaks of disease such as hantavirus, Lassa fever, monkeypox, encephalitis, tuberculosis, measles, AIDS, smallpox, polio, Legionnella, Guillain–Barré syndrome, SARS, syphilis, PPNG, babesiosis, and cholera.
PHAs were assigned to work in health campaigns such as Guinea worm, malaria, syphilis, diarrheal diseases, yellow fever, yaws, swine flu, and measles.
PHAs have been sent to respond to major events such as floods, hurricanes, volcanic eruptions, earthquakes, and the anthrax scare in the U.S.[11] They even were assigned to be poll watchers in select Southern states during the 1972 and 1976 presidential elections.