Open AccessPopulation density and basic reproductive number of COVID-19 across United States counties
Author(s) -
Karla Therese Sy,
Laura F. White,
Brooke E Nichols
Publication year - 2021
Publication title -
plos one
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.99
H-Index - 332
ISSN - 1932-6203
DOI - 10.1371/journal.pone.0249271
Subject(s) - population density , demography , population , outbreak , geography , transmission (telecommunications) , population size , medicine , virology , sociology , electrical engineering , engineering
The basic reproductive number (R 0 ) is a function of contact rates among individuals, transmission probability, and duration of infectiousness. We sought to determine the association between population density and R 0 of SARS-CoV-2 across U.S. counties. We conducted a cross-sectional analysis using linear mixed models with random intercept and fixed slopes to assess the association of population density and R 0 , and controlled for state-level effects using random intercepts. We also assessed whether the association was differential across county-level main mode of transportation percentage as a proxy for transportation accessibility, and adjusted for median household income. The median R 0 among the United States counties was 1.66 (IQR: 1.35–2.11). A population density threshold of 22 people/km 2 was needed to sustain an outbreak. Counties with greater population density have greater rates of transmission of SARS-CoV-2, likely due to increased contact rates in areas with greater density. An increase in one unit of log population density increased R 0 by 0.16 (95% CI: 0.13 to 0.19). This association remained when adjusted for main mode of transportation and household income. The effect of population density on R 0 was not modified by transportation mode. Our findings suggest that dense areas increase contact rates necessary for disease transmission. SARS-CoV-2 R 0 estimates need to consider this geographic variability for proper planning and resource allocation, particularly as epidemics newly emerge and old outbreaks resurge.