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Physical Distancing

Last updated: November 17, 2020 

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The following is a curated review of key information and literature about this topic. It is not comprehensive of all data related to this subject.

Overview

SARS-CoV-2 is believed to spread primarily through close person-to-person contact because its transmission correlates to duration and distance of physical interaction. Respiratory droplets, which are produced when people speak, cough, sneeze and sing, appear to be the predominant mode of transmission. For additional information on routes of transmission of SARS-CoV-2, please see the Personal Protective Equipment in Medical Settings section.

Because most respiratory droplets can travel up to 6 feet, CDC recommends physical distancing, also called “social distancing,” which means keeping a space of at least 6 feet between people who do not live in the same household. Limiting travel outside the home may also be helpful. There may be certain scenarios where distancing alone is inadequate, and therefore a combination of strategies such as masking, hand hygiene and physical distancing is likely most effective.

Physical distancing seeks to limit transmission through “close contact,” which CDC defines as being within 6 feet of an infected person for a cumulative total of 15 minutes or more (e.g., three five-minute exposures for a total of 15 minutes) over a 24-hour period, starting from two days before illness onset (or, for asymptomatic patients, two days prior to test specimen collection).

Current data on physical distancing to prevent SARS-CoV-2 transmission is limited to observational studies and the extrapolation of data on other respiratory viruses.

Key Findings

In summary: Overall, based on epidemiologic and observational studies, physical distancing, limiting contact outside the household and quarantine are associated with reductions in the transmission of SARS-CoV-2.

Longitudinal pretest-posttest comparison group study to estimate the change in COVID-19 case growth before and after statewide social distancing measures in the United States (Siedner, August 2020).

  • An assessment of timing of statewide physical distancing measures and COVID-19 case growth rates.
  • Mean daily COVID-19 case growth rate decreased by 0.9% per day beginning 4 days after implementation of the first statewide social distancing measures (P < 0.001).
  • Beginning 7 days after physical distancing, the COVID-19 mortality growth rate decreased by 2.0% per day (P < 0.001); this decrease was no longer statistically significant by 10 days.
  • This is an observational study and may be limited by confounding factors.

A cohort study examining the association of social distancing, population density, and temperature with SARS-CoV-2 reproduction number over time (Rt) in counties across the United States (Rubin, July 2020).

  • Physical distancing was measured by percentage change in visits to nonessential businesses.
  • In a multivariable analysis, a 50% decrease in visits to nonessential businesses was associated with a 45% decrease in Rt.

Survey study of people in Maryland regarding the adoption of non-pharmaceutical interventions (Clipman, July 2020).

  • 1,030 people were sampled. The median age of the sample was 43 years. 96% had traveled outside of their homes unrelated to work
  • 55 participants (5.3%) self-reported testing positive for SARS-CoV-2 
  • In multivariable analysis, SARS-CoV-2 infection was negatively associated with physical distancing (adjusted odds ratio: 0.10; 95% CI: 0.03 - 0.33)
  • This is a survey-based study, and so may be affected by recall bias.

Mathematical modeling study examining the association between mobility patterns and COVID-19 transmission in the United States (Badr, July 2020).

  • Cell phone data capturing movement patterns in U.S. counties was used to evaluate how physical distancing affected the rate of new infections.
  • Mobility patterns were correlated with decreased COVID-19 growth rates, with a Pearson correlational coefficient of more than 0.7 for 20 of the 25 counties assessed.
  • As a modeling study, subject to potential error based on the assumptions used to create the model.

A systematic review and meta-analysis of physical distancing, face masks, and eye protection to transmission of SARS-CoV-2 (Chu, June 2020).

  • Review of 172 observational studies in healthcare and non-healthcare settings of > 20,000 patients with COVID-19, MERS, or SARS.
  • Maintaining at least 1 meter of physical distance was associated with lower transmission of virus (n=10,736, pooled adjusted odds ratio 0.18, 95% CI 0.09-0.38); protection increased as distance was lengthened (change in relative risk 2.02/m; pinteraction=0.041). 

A Cochrane review assessing the effects of quarantine alone or in combination with other measures on COVID-19 control (Nussbaumer-Streit, April 2020).

  • Studies reviewing the effect of measures on SARS, MERS, and SARS-CoV-2 were included.
  • Modeling studies reported the quarantine of people exposed to confirmed or suspected cases averted 44% to 81% incident cases and 31% to 63% of deaths compared to no measures based on different scenarios (low-certainty evidence).
  • When the models combined quarantine with other prevention and control measures (school closures, travel restrictions and physical distancing), they demonstrated a larger effect on the reduction of new cases, transmissions and deaths than individual measures alone (low-certainty evidence).

 

Additional Literature

The impact of social distancing on COVID-19 spread: State of Georgia case study (Keskinocak, October 2020).

An agent-based simulation model to project infection spread in Georgia was developed over 7.5 months, testing different social distancing scenarios, including baselines (no-intervention or school closure only) and combinations of shelter-in-place and voluntary quarantine with different timelines and compliance levels. Compared to peak infections of approximately 180,000 with no intervention and 113,000 with school closure, the model predicted   reduced the peak to below 53,000 and delayed it from April to July or later. Increasing shelter-in-place duration from four to five weeks yielded a 2–9% decrease in cumulative infections and a 3–11% decrease in cumulative deaths.  

 

Epidemic mathematical modeling study investigating the effectiveness of social distancing interventions in Seattle, Washington (Matrajt, August 2020).

Interventions reduced contacts of adults >60 years of age, adults 20–59 years of age, and children <19 years of age for 6 weeks. Interventions started earlier in the epidemic delay the epidemic curve and interventions started later flatten the epidemic curve.

Social distancing alters the clinical course of COVID-19 in young adults: A comparative cohort study (Bielecki, June 2020).

Study of 508 soldiers in Switzerland. SARS-CoV-2 infection was examined before and after physical distancing was implemented during an outbreak. 354 soldiers were infected prior to physical distancing, and 30% developed symptoms. 154 soldiers had positive tests after physical distancing; none had symptoms.

Mathematical modeling study seeking to determine the impact of stay-at-home and shelter-in-place orders on COVID-19 transmission in the United States (Fowler, April 2020).

The authors’ model estimated that stay-at-home and shelter-in-place policies reduced COVID-19 infections from a mean incidence reduction of 3.9% one week after implementation (95% CI: 1.2 – 6.6%) to a 22.6% mean reduction 27 days after implementation (95% CI: 14.8 – 30.5%).

 

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