25. Basic Reproduction Number

Lecture Summary The basic reproduction number, R0 (R zero or R naught) is a measurement used in epidemiology focused on the infectivity of a given pathogen. It attempts to predict how many people will become infected by one infected person in the absence of any immunity within a given population. It is not a biological constant and can be affected by human behavior, societal infrastructure, geography, and climate. Key Points - The basic reproduction number is not a constant, It depends on time, location, and can change based on the particular mathematical model used for calculation. - R0 is not based on time in anyway. An individual infected with HIV has their entire life to spread the virus. On the contrary, someone with COVID19 has only about a week. - The most important number regarding R0 is 1. If the R0 is above 1, the infection will spread. If R0 is below one, the infection will eventually die off. - Humans can alter the R0 of an infection with behavior, the goal is almost always to lower the number to < 1. - Infections are spread in different ways. Examples include aerosol generation, respiratory droplets, contact with body fluids, and the fecal to oral route. - Various infection control measures are utilized in the healthcare setting to combat these including masks, gloves, gowns, and other barrier protections. - Many of the infections with the highest R0 values have effectively been vaccinated out of our populations. Examples include measles, chickenpox, mumps, rubella, pertussis, and smallpox. We have forgotten the morbidity and mortality associated with these infections in a matter of decades. - Let’s compare Measles, HIV/AIDs, and SARs CoV-2 with regard to basic reproduction number. Listen to the show for this! - This is the first of a 4 part series, that will also cover smallpox, emerging infectious diseases, basic vaccine design, and the new messenger RNA. Saddle up! References - van den Driessche P. Reproduction numbers of infectious disease models. Infect Dis Model. 2017;2(3):288-303. Published 2017 Jun 29. doi:10.1016/j.idm.2017.06.002 - Delamater PL, Street EJ, Leslie TF, et al. Complexity of the Basic Reproduction Number (R0). Emerging Infectious Diseases. 2019;25(1):1-4. doi:10.3201/eid2501.171901. - Katul GG, Mrad A, Bonetti S, Manoli G, Parolari AJ (2020) Global convergence of COVID-19 basic reproduction number and estimation from early-time SIR dynamics. PLOS ONE 15(9): e0239800. https://doi.org/10.1371/journal.pone.0239800 - Wikipedia, Basic Reproduction Number, Measles, COVID19, HIV - CDC, transmission based precautions. Available at: https://www.cdc.gov/infectioncontrol/basics/transmission-based-precautions.html - Tanne Janice Hopkins. Measles cases and deaths are increasing worldwide, warn health agencies BMJ 2020; 371 :m4450