Population density and basic reproductive number of COVID-19 across United States counties

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Abstract

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.

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  1. SciScore for 10.1101/2020.06.12.20130021: (What is this?)

    Please note, not all rigor criteria are appropriate for all manuscripts.

    Table 1: Rigor

    NIH rigor criteria are not applicable to paper type.

    Table 2: Resources

    Software and Algorithms
    SentencesResources
    All analyses was conducted in R version 4.0.0.24 The figure and removal of adjacent counties in the sensitivity analyses were done with ArcGIS.
    ArcGIS
    suggested: (ArcGIS for Desktop Basic, RRID:SCR_011081)

    Results from OddPub: Thank you for sharing your code and data.


    Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:
    Our study has a number of limitations. While we demonstrate that population density is associated with R0, we estimated R0 based on the number of reported cases; therefore, the incidence of COVID-19 across US counties may …