Social distancing

Social distancing is a term applied to certain nonpharmaceutical infection control actions that are taken by public health officials to stop or slow down the spread of a highly contagious disease. The objective of social distancing is to reduce the probability of contact between persons carrying an infection, and others who are not infected, so as to minimize disease transmission, morbidity and ultimately, mortality.[1]

Social distancing is most effective when the infection can be transmitted via droplet contact (coughing or sneezing); direct physical contact, including sexual contact; indirect physical contact (e.g. by touching a contaminated surface such as a fomite); or airborne transmission (if the microorganism can survive in the air for long periods).[2]

Social distancing may be less effective in cases where the infection is transmitted primarily via contaminated water or food or by vectors such as mosquitoes or other insects, and less frequently from person to person.[3]

One of the earliest references to social distancing dates to the seventh century BC in the Book of Leviticus, 13:46: "And the leper in whom the plague is...he shall dwell alone; [outside] the camp shall his habitation be."[4]

Historically, leper colonies and lazarettos were established as a means of preventing the spread of leprosy and other contagious diseases through social distancing,[5] until transmission was understood and effective treatments were invented.


Some examples of social distancing used to control the spread of contagious illnesses include:[6]

  • school closure (proactive or reactive)[7]
  • workplace closure [8] including closure of “non-essential” businesses and social services. “Non-essential” means those facilities that do not maintain primary functions in the community, as opposed to essential services.[9]
  • isolation (health care)
  • quarantine
  • cordon sanitaire
  • protective sequestration
  • cancellation of mass gatherings such as sports events, films or musical shows.[10]
  • shutting down or limiting mass transit
  • closure of recreational facilities (community swimming pools, youth clubs, gymnasiums).[11]
  • "self-shielding" measures for individuals include limiting face-to-face contacts, conducting business by phone or online, avoiding public places and reducing unnecessary travel.[12][13] The "elbow bump" and the "Dracula sneeze" are additional measures to reduce direct person-to-person transmission of microorganisms.[14]


Research indicates that measures must be applied rigorously and immediately in order to be effective.[15] During the 1918 flu pandemic, authorities in the US implemented school closures, bans on public gatherings, and other social distancing interventions in Philadelphia and in St. Louis, but in Philadelphia the delay of five days in initiating these measures allowed transmission rates to double three to five times, whereas a more immediate response in St. Louis was significant in reducing transmission there.[16] Bootsma and Ferguson analyzed social distancing interventions in 16 US cities during the 1918 epidemic and found that time-limited interventions reduced total mortality only moderately (perhaps 10–30%), and that the impact was often very limited because the interventions were introduced too late and lifted too early. It was observed that several cities experienced a second epidemic peak after social distancing controls were lifted, because susceptible individuals who had been protected were now exposed.[17]

School closures

School closures were shown to reduce morbidity from the Asian Flu by 90% during the 1957-58 outbreak,[18] and up to 50% in controlling influenza in the US, 2004-2008.[19] Similarly, mandatory school closures and other social distancing measures were associated with a 29% to 37% reduction in influenza transmission rates during the 2009 flu epidemic in Mexico.[20]

Workplace closures

Modeling and simulation studies based on US data suggest that if 10% of affected workplaces are closed, the overall infection transmission rate is around 11.9% and the epidemic peak time is slightly delayed. In contrast, if 33% of affected workplaces are closed, the attack rate decreases to 4.9%, and the peak time is delayed by 1 week.[21]

Quarantine of contacts and suspected cases

During the 2003 SARS outbreak in Singapore, some 8,000 persons were subjected to mandatory home quarantine and an additional 4,300 were required to self-monitor for symptoms and make daily telephone contact with health authorities as a means of controlling the epidemic. Although only 58 of these individuals were eventually diagnosed with SARS, public health officials were satisfied that this measure assisted in preventing further spread of the infection.[22] Voluntary self-isolation may have helped reduce transmission of influenza in Texas in 2009.[23]

Cordon sanitaire

In 1995 a cordon sanitaire was used to control an outbreak of Ebola virus disease in Kikwit, Zaire.[24][25][26] President Mobutu Sese Seko surrounded the town with troops and suspended all flights into the community. Inside Kikwit, the World Health Organization and Zaire medical teams erected further cordons sanitaires, isolating burial and treatment zones from the general population and successfully containing the infection.[27] During the 2003 SARS outbreak in Canada, "community quarantine" was used to reduce transmission of the disease with moderate success.[28]

Protective sequestration

During the 1918 influenza epidemic the town of Gunnison, Colorado isolated itself for two months to prevent an introduction of the infection. All highways were barricaded near the county lines. Train conductors warned all passengers that if they stepped outside of the train in Gunnison, they would be arrested and quarantined for five days. As a result of the isolation, no one died of influenza in Gunnison during the epidemic.[29] Several other communities adopted similar measures.[30]

Canceling mass gatherings

Evidence suggesting that mass gatherings increase the potential for infectious disease transmission is inconclusive.[31] Anecdotal evidence suggests that certain types of mass gatherings may be associated with increased risk of influenza transmission, and may also "seed" new strains into an area, instigating community transmission in a pandemic. During the 1918 influenza pandemic, military parades in Philadelphia[32] and Boston[33] may have been responsible for spreading the disease by mixing infected sailors with crowds of civilians. Restricting mass gatherings, in combination with other social distancing interventions, may help reduce transmission.[34]

Travel restrictions

Border restrictions and/or internal travel restrictions are unlikely to delay an epidemic by more than 2–3 weeks unless implemented with over 99% coverage.[35] Airport screening was found to be ineffective in preventing viral transmission during the 2003 SARS outbreak in Canada[36] and the US.[37] Strict border controls between Austria and the Ottoman Empire, imposed from 1770 until 1871 to prevent persons infected with the bubonic plague from entering Austria, were reportedly effective, as there were no major outbreaks of plague in Austrian territory after they were established, whereas the Ottoman Empire continued to suffer frequent epidemics of plague until the mid-nineteenth century.[38]

See also


  1. Pandemic Planning - Social Distancing Fact Sheet
  2. "Information about Social Distancing," Santa Clara Public Health Department.
  3. "Interim Pre-Pandemic Planning Guidance: Community Strategy for Pandemic Influenza Mitigation in the United States—Early, Targeted, Layered Use of Nonpharmaceutical Interventions," CDC, Feb 2007
  4. Bible Gateway, Authorized King James Version, Leviticus 13:46
  5. Charles Léon Souvay, "Leprosy," Catholic Encyclopedia (1913), Volume 9.
  6. Kathy Kinlaw, Robert Levine, "Ethical Guidelines on Pandemic Influenza," CDC, December 2006
  7. Cauchemez S, Ferguson NM, Wachtel C, Tegnell A, Saour G, Duncan B, Nicoll A (2009). "Closure of schools during an influenza pandemic". The Lancet Infectious Diseases. 9 (8): 473–481. doi:10.1016/s1473-3099(09)70176-8. PMID 19628172.
  8. Kumar S, Crouse Quinn S, Kim KH, Daniel LH, Freimuth VS (2012). "The Impact of Workplace Policies and Other Social Factors on Self-Reported Influenza-Like Illness Incidence During the 2009 H1N1 Pandemic". American Journal of Public Health. 102 (1): 134–140. doi:10.2105/AJPH.2011.300307. PMC 3490553. PMID 22095353.
  9. "Social Distancing Support Guidelines," Colorado Dept. of Public Health and Environment, March 2008.
  10. R. Booy and J. Ward, "Evidence compendium and advice on social distancing and other related measures for response to an influenza pandemic," National Centre for Immunisation Research and Surveillance.
  11. "Flu Pandemic Mitigation - Social Distancing"
  12. Glass RJ, Glass LM, Beyeler WE, Min HJ. "Targeted Social Distancing Designs for Pandemic Influenza." Emerg Infect Dis. 2006;12(11):1671-1681.
  13. "Social Distancing Guidelines (for workplace communicable disease outbreaks)"
  14. "Guidance on Preparing Workplaces for an Influenza Pandemic," OSHA 3327-02N 2007
  15. Maharaj S, Kleczkowski A (2012). "Controlling epidemic spread by social distancing: Do it well or not at all". BMC Public Health. 12 (1): 679. doi:10.1186/1471-2458-12-679. PMC 3563464. PMID 22905965.
  16. Hatchett RJ, Mecher CE, Lipsitch M (2007). "Public health interventions and epidemic intensity during the 1918 influenza pandemic". Proc Natl Acad Sci U S A. 104 (18): 7582–7587. doi:10.1073/pnas.0610941104. PMC 1849867. PMID 17416679.
  17. Bootsma MC, Ferguson NM (2007). "The effect of public health measures on the 1918 influenza pandemic in U.S. cities". Proc Natl Acad Sci U S A. 104 (18): 7588–7593. doi:10.1073/pnas.0611071104. PMC 1849868. PMID 17416677.
  18. Chin TD, Foley JF, Doto IL, Gravelle CR, Weston J (1960). "Morbidity and mortality characteristics of Asian strain influenza". Public Health Rep. 75 (2): 148–58. doi:10.2307/4590751. JSTOR 4590751. PMC 1929395. PMID 19316351.
  19. Wheeler CC, Erhart LM, Jehn ML (2010). "Effect of school closure on the incidence of influenza among school -age children in Arizona". Public Health Reports. 125 (6): 851–859. doi:10.1177/003335491012500612. PMC 2966666. PMID 21121230.
  20. Flu Pandemic Study Supports Social Distancing," NIH Research Matters, June 6, 2011.
  21. Rousculp MD, Johnston SS, Palmer LA, Chu BC, Mahadevia PJ, Nichol KL (2010). "Attending work while sick: implication of flexible sick leave policies". Journal of Occupational and Environmental Medicine. 52 (10): 1009–1013. doi:10.1097/jom.0b013e3181f43844. PMID 20881626.
  22. Chorh-Chuan Tan, "SARS in Singapore – Key Lessons from an Epidemic," Annals Academy of Medicine, May 2006, Vol. 35 No.5.
  23. Teh B, Olsen K, Black J, Cheng AC, Aboltins C, Bull K, et al. (2012). "Impact of swine influenza and quarantine measures on patients and households during the H1N1/09 pandemic". Scandinavian Journal of Infectious Diseases. 44 (4): 289–296. doi:10.3109/00365548.2011.631572. PMID 22106922.
  24. Laurie Garrett, "Heartless but Effective: I've Seen 'Cordon Sanitaire' Work Against Ebola," The New Republic, August 14, 2014
  25. "Outbreak of Ebola Viral Hemorrhagic Fever -- Zaire, 1995" Morbidity and Mortality Weekly Report, May 19, 1995 / 44(19);381-382
  26. Rachel Kaplan Hoffmann and Keith Hoffmann, "Ethical Considerations in the Use of Cordons Sanitaires," Clinical Correlations, February 19, 2015.
  27. Laurie Garrett, Betrayal of Trust: The Collapse of Global Public Health, Hachette Books, 2011 ISBN 1401303862
  28. Bondy SJ, Russell ML, Laflèche JM, Rea E (2009). "Quantifying the impact of community quarantine on SARS transmission in Ontario: estimation of secondary case count difference and number needed to quarantine". BMC Public Health. 9 (1): 488. doi:10.1186/1471-2458-9-488. PMC 2808319. PMID 20034405.
  29. Gunnison: Case Study, University of Michigan Medical School, Center for the History of Medicine
  30. H. Markel, A.M. Stern, J. A. Navarro, J. R. Michalsen, A. S. Monto, and C. DiGiovanni, "Nonpharmaceutical Influenza Mitigation Strategies, US Communities, 1918–1920 Pandemic," Emerging Infectious Diseases, Vol. 12, No. 12, December 2006.
  31. Thomas V. Inglersby et al, "Disease Mitigation Measures in the Control of Pandemic Influenza," Biosecurity and Bioterrorism Biodefense Strategy & Science, Volume 4, Number 4,2006
  32. Kenneth C. Davis, "Philadelphia Threw a WWI Parade That Gave Thousands of Onlookers the Flu,", September 21, 2018
  33. "The Flu in Boston," American Experience, WGBH
  34. Ishola DA, Phin N (2011). "Could influenza transmission be reduced by restricting mass gatherings? Towards an evidence-based policy framework". Journal of Epidemiology and Global Health. 1 (1): 33–60. doi:10.1016/j.jegh.2011.06.004. PMID 23856374.
  35. Ferguson NM, Cummings DA, Fraser C, Cajka JC, Cooley PC, Burke DS (2006). "Strategies for mitigating an influenza pandemic". Nature. 442 (7101): 448–52. doi:10.1038/nature04795. PMID 16642006.
  36. Bell DM, World, Community (2004). "Public health interventions and SARS spread, 2003". Emerg Infect Dis. 10 (11): 1900–1906. doi:10.3201/eid1011.040729. PMC 3329045. PMID 15550198.
  37. Martin Cetron, et al. "Isolation and Quarantine: Containment Strategies for SARS, 2003." From Learning from SARS: Preparing for the Next Disease Outbreak, National Academy of Sciences, 2004. ISBN 0309594332
  38. George C. Kohn, Encyclopedia of Plague and Pestilence: From Ancient Times to the Present, Infobase Publishing, 2007; p. 30. ISBN 1438129238
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