Critical community size

Short description: Minimum size of a closed population within which a pathogen can persist indefinitely

The critical community size (CCS) is the minimum size of a closed population within which a human-to-human, non-zoonotic pathogen can persist indefinitely.^[1]

When the size of the closed population falls below the critical community size level, the low density of infected hosts causes extinction of the pathogen.^[2] This epidemiologic phenomenon was first identified during measles outbreaks in the 1950s.^[1]

The critical community size depends on:^[3]

Speed of transmission
How long until a person who has recovered remains immune
Fatality rate
Birth and death rate in the general population

References

↑ ^1.0 ^1.1 Bartlett, M. S. (1960). "The critical community size for measles in the United States". Journal of the Royal Statistical Society. Series A (General) 123 (1): 37–44. doi:10.2307/2343186.
↑ Haydon, Daniel T; Cleaveland, Sarah; Taylor, Louise H; Laurenson, M Karen (2002). "Identifying reservoirs of infection: a conceptual and practical challenge". Emerging Infectious Diseases 8 (12): 1468–1473. doi:10.3201/eid0812.010317. PMID 12498665.
↑ "Modelling of contact tracing in determining critical community size for infectious diseases". Chaos, Solitons & Fractals 159. June 2022. doi:10.1016/j.chaos.2022.112141.