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. 2021 Apr 21;16(4):e0249271. doi: 10.1371/journal.pone.0249271

Fig 2. Population density threshold required to establish a sustained outbreak in United States counties.

Fig 2

A population density of approximately 22 people/km2 was needed to sustain an outbreak, which is approximately equal to the lower IQR of the counties with established COVID-19 outbreaks [median = 53.8 population/km2; IQR = 21.24, 144.05], and a slightly less than the upper IQR of the counties with no COVID-19 outbreaks [median = 11.3 population/km2; IQR = 3.56, 23.88]. The grey circles represent the individual county population densities.