Several factors affect the incidence of syphilis. The number of infectious cases in the population, sexual promiscuity, the high rate of communicability and mass shifts in population, such as those caused by mobilization, militate towards its increase. Conversely intensive casefinding, including contact investigation, public education and mass testing, diagnosis and treatment, prophylaxis, and other preventive measures, militates towards its reduction.
Chart 1 shows the rapid decline of early syphilis in the United States since 1947. The decline in the estimated annual minimum incidence of syphilis derives mainly from more than a decade of intensive effort to find and treat persons with the early stages of the disease. They are not easy to find. Over the years a method of early case finding known as contact investigation has been developed and refined. Early syphilis patients are interviewed to obtain names, addresses, and other identifying data of all their sexual partners. Skilled
Bauer TJ. PUBLIC HEALTH PROBLEMS IN SYPHILIS CONTROL. JAMA. 1953;152(4):300–303. doi:10.1001/jama.1953.03690040004002