Parran Award Lecture: insights into the epidemiology of sexually transmitted diseases from Ro = betacD.

Because the Thomas Parran Award is the highest honor in the field of sexually transmitted disease (STD) prevention and research, I am humbled and honored to be this year’s recipient. I want to express my thanks to the Association and the Award Committee for this great honor. Any lifetime achievement award results from a lifetime of influences and my experience is no different. I owe an extraordinary debt of gratitude to King Holmes, Allan Ronald, and Roy Anderson. They have shaped how I think about STD research and their ideas repeatedly appear in my work. I also owe thanks to the many colleagues and students with whom I have worked over the years. In particular, I want to acknowledge the pleasures of working with Frank Plummer, Stephen Moses, Joshua Kimani, Fred Aoki, Jamie Blanchard, Rosanna Peeling, Grant McClarty, Michael Rekart, David Patrick, Babak Pourbohloul, and Craig Cohen. My 23-year career as an academic physician entirely depended on the constant support that I received from my wife and 2 sons. I am forever thankful for their unending patience and encouragement. The basic reproduction number (Ro) is fundamental to understanding infectious disease epidemiology. Ro describes the average number of secondary infections that an infected individual generates when entering a fully susceptible population, and when greater than one, it defines ecologic success for a pathogen. Natural selection acts to optimize Ro when an emerging infectious disease newly enters a species population, thus shaping the genotypic and phenotypic properties of a microbe. A range of Ro values have been computed for different pathogens depending on factors such as routes and density dependence of transmission and susceptibility of the pathogen to innate and adaptive immune defenses.1,2 The concept of the reproduction number has been critical to understanding the epidemiology of sexually transmitted infections (STIs)3 and has helped rationalize prevention strategies.4 Ro is determined by 3 parameters: , which represents the per-capita transmissibility of the agent; D, the average annualized duration of infection; and c, the pattern of contact between susceptible and infectious persons: