Syphilis Cycles

Syphilis has re-emerged as a global public health issue. In lesser developed countries, millions of people are contracting the disease, which can be fatal without access to proper treatment. In developed countries, prevalence is on the rise and has cycled around endemic levels for decades. We investigate syphilis dynamics by extending the classic SIRS epidemiological model to incorporate forward-looking, rational individuals and the AIDS epidemic. The integrated economic-epidemiological model shows that human preferences over health and sexual activity are central to the nature of syphilis cycles. We find that low-activity individuals will behave in a manner that significantly dampen the cycles, while high-activity individuals will tend to exacerbate the cycles, a phenomenon we refer to as rational dynamic resonance. The model also provides insights into two failed attempts by the U.S. government to eradicate syphilis from the U.S. population.