Real-time, interactive website for US-county-level COVID-19 event risk assessment

Abstract

Large events and gatherings, particularly those taking place indoors, have been linked to multitransmission events that have accelerated the pandemic spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). To provide real-time, geolocalized risk information, we developed an interactive online dashboard that estimates the risk that at least one individual with SARS-CoV-2 is present in gatherings of different sizes in the United States. The website combines documented case reports at the county level with ascertainment bias information obtained via population-wide serological surveys to estimate real-time circulating, per-capita infection rates. These rates are updated daily as a means to visualize the risk associated with gatherings, including county maps and state-level plots. The website provides data-driven information to help individuals and policy makers make prudent decisions (for example, increasing mask-wearing compliance and avoiding larger gatherings) that could help control the spread of SARS-CoV-2, particularly in hard-hit regions.

Figure 1.. Heterogeneous risk map.

The map depicts risk given events of size 50 using ascertainment biases of 10x (A) and 5x (B) on May 1, June 1, July 1 and August 1. Alaska and Hawaii were resized to be smaller than they actually are on the web.

Figure 2.. Visualizations of event-associated risk.

An entropy-based index of heterogeneity in risk reveals that intermediate event sizes differentiate spatially heterogeneous risk as of August 1, 2020. (A) Visualization entropy as a function of event size using 5x and 10x ascertainment biases for events between sizes 10 and 1000. (B) Maps illustrating that most counties appear to have similarly low risk when events are small (<10 individuals) or similarly high risk when events large (>1000 individuals). In contrast, the highest level of heterogeneity in risk is revealed given intermediate event sizes (50–150 individuals). Map visualizations use an assumption of 5x ascertainment bias.

Figure 3.. State-level risk associated with events of size 50 over time.

The curves denote risk estimates assuming 5:1 (dark blue) and 10:1 (light blue) ascertainment biases. States are ordered as a function of ascending risk level as of August 14, 2020 (last point shown).