Differences in rapid increases in county-level COVID-19 incidence by implementation of statewide closures and mask mandates - United States, June 1-September 30, 2020

Abstract

Background and objective: Community mitigation strategies could help reduce COVID-19 incidence, but there are few studies that explore associations nationally and by urbanicity. In a national county-level analysis, we examined the probability of being identified as a county with rapidly increasing COVID-19 incidence (rapid riser identification) during the summer of 2020 by implementation of mitigation policies prior to the summer, overall and by urbanicity.

Methods: We analyzed county-level data on rapid riser identification during June 1-September 30, 2020 and statewide closures and statewide mask mandates starting March 19 (obtained from state government websites). Poisson regression models with robust standard error estimation were used to examine differences in the probability of rapid riser identification by implementation of mitigation policies (P-value< .05); associations were adjusted for county population size.

Results: Counties in states that closed for 0-59 days were more likely to become a rapid riser county than those that closed for >59 days, particularly in nonmetropolitan areas. The probability of becoming a rapid riser county was 43% lower among counties that had statewide mask mandates at reopening (adjusted prevalence ratio = 0.57; 95% confidence intervals = 0.51-0.63); when stratified by urbanicity, associations were more pronounced in nonmetropolitan areas.

Conclusions: These results underscore the potential value of community mitigation strategies in limiting the COVID-19 spread, especially in nonmetropolitan areas.

Keywords: COVID-19; Closures; Mask mandates; Mitigation strategies.

Fig. 1

Length of statewide closures and states with mask mandates in place at reopening United States, March 19September 30, 2020* *The length of statewide closure was defined as starting on the earlier of either 1) the date persons in all counties were required to stay home or 2) the date both restaurants were required to cease any on-premises dining and nonessential retail businesses were ordered to close in all counties; the earliest date one of these restrictions were lifted for all counties was defined as the statewide reopening. The start date of statewide mask mandate was defined as the date that persons operating in a personal capacity were required to wear masks 1) anywhere outside the home or 2) both in retail businesses and in restaurants/food establishments. (created with mapchart.net)

Fig. 2

Adjusted^ prevalence ratios and 95% confidence intervals comparing rapid riser* identification during June 1–September 30, 2020 by length of statewide closure (days)⁺, stratified by urbanicity. Figure 2 Footnotes: ^Adjusted for population size; * Rapid riser counties were defined as those that met the following criteria: 1) >100 new cases in the last 7 days, 2) >0% change in the 7-day incidence, 3) a decrease of no more than 60% or an increase in the most recent 3-day COVID-19 incidence over the preceding 3-day incidence, and 4) a 7-day incidence/30-day incidence ratio >0.31. In addition, rapid riser counties met one or both of the following triggering criteria: 1) >60% change in 3-day incidence, or 2) >60% change in 7-day incidence. +Each statewide closure length category compared to reference category of statewide closure >59 days.

Fig. 3

Adjusted^ prevalence ratios and 95% confidence intervals comparing rapid riser* identification during June 1–September 30, 2020 by statewide mask mandate upon statewide reopening, stratified by urbanicity. Figure 3 Footnotes: ^Adjusted for population size. *Rapid riser counties were defined as those that met the following criteria: (1) >100 new cases in the last 7 days, (2) >0% change in the 7-day incidence, (3) a decrease of no more than 60% or an increase in the most recent 3-day COVID-19 incidence over the preceding 3-day incidence, and (4) a 7-day incidence/30-day incidence ratio >0.31. In addition, rapid riser counties met one or both of the following triggering criteria: (1) >60% change in 3-day incidence, or (2) >60% change in 7-day incidence.