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:[citation needed]
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