pmcEmerg Infect DisEmerg Infect DisEIDEmerging Infectious Diseases1080-60401080-6059Centers for Disease Control and Prevention1037084122-144510.3201/eid2908.221445EtymologiaEtymologiaReproduction NumberEtymologia: Reproduction NumberReproduction NumberSharmaVijaySharmaRajnishSinghBalbir B.Guru Angad Dev Veterinary and Animal Sciences University, Punjab, IndiaAddress for correspondence: Balbir B. Singh, Centre for One Health, Guru Angad Dev Veterinary and Animal Sciences University, Ludhiana, Punjab 141004, India; email: bbsdhaliwal@gmail.com82023298154715472023https://creativecommons.org/licenses/by/4.0/Emerging Infectious Diseases is a publication of the U.S. Government. This publication is in the public domain and is therefore without copyright. All text from this work may be reprinted freely. Use of these materials should be properly cited.Keywords: etymologiareproduction numberbasic reproductive numberR0effective reproductive numberRtZ0epidemicsnew casesinfectionsepidemiologymathematical epidemiologydisease susceptibilitymalariaGeorge Macdonald

Reproduction Number [′ṝe-prə-′dak-shən ′nəm-bər]

The basic reproduction number (R0, pronounced R naught) is derived from demography terminology used to estimate the overall population reproduction rate. R0 is an essential metric in the study of epidemics (Figure). This value measures the estimated number of new cases of an infection caused by an infectious person in a population of disease-susceptible person.

History and concept of basic reproduction number (R0). *The total reproduction of the population.

The effective reproduction number (Rt) is similar to R0, but Rt measures the number of persons infected by infectious person when some portion of the population has already been infected. This idea can be traced back to the work performed by Richard Bockh, Alfred Lotka and others.

A modern application of R0 in epidemiology was reported in 1952 when George Macdonald constructed population models about the spread of malaria. Macdonald used the notation Z0 instead of R0 to differentiate it from the preceding demography terminology. The notation R0 was adopted instead of Z0 during the Dahlem conference in 1982.

Suggested citation for this article: Sharma V, Sharma R, Singh BB. Etymologia: reproduction number. Emerg Infect Dis. 2023 Aug [date cited]. https://doi.org/10.3201/eid2908.221445

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