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Two metres or one: what is the evidence for physical distancing in covid-19?

BMJ 2020; 370 doi: https://doi.org/10.1136/bmj.m3223 (Published 25 August 2020) Cite this as: BMJ 2020;370:m3223

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Specific measurements defining crowding for physical distancing in covid-19. Re: Two metres or one: what is the evidence for physical distancing in covid-19?

Dear Editor

Although the article “Two metres or one: what is the evidence for physical distancing in covid-19?” by Jones NR et al.,1 published in BMJ 2020;370:m3223 on 25 August 2020, reports sound and practical information on protecting people from SARS-CoV-2 infection, information on “occupancy or crowding level” and definitions of low and high occupancies are not provided. The Oxford Dictionary of English defines crowd as “a large number of people gathered together in a disorganized and unruly way”.2 This definition is insufficient for scientific studies, and specific measurements defining crowding are necessary.
The World Health Organization states that crowding in housing relates to the conditions of the dwelling and the space it offers, in addition to the number of people sharing the dwelling.3 This definition allows for relative comparisons. For example, which scenario is more crowded: three persons in a lift of 1 m2, 50 people in a 200 m2 supermarket or six healthcare workers doing ward rounds in 4 m2 patient rooms? Although there is no universally accepted measure for overcrowding, the U.S. Department of Housing and Urban Development Office of Policy Development and Research has reported on the benefits of several methods of measuring overcrowding, such as persons-per-room (PPR) and unit square footage-per-person (USFPP).4 Typically, the number of standing passengers per square meter is an objective standard measure for crowding used by many public transport services around the world.5 Presently, in public areas, such as public transport vehicles, bars and restaurants, and even in hospital wards, intensive care units, training meeting halls and operating theatres, there is ambiguity in the appropriate methods of protection against COVID-19 infection.6 The study conducted by Jones NR et al.1 provides useful information on protecting people from COVID-19 but, in order to best interpret the results of such a study involving crowd parameters, it is necessary to apply one of the crowd measurement methods reported in the literature.

References
1. Jones N, Qureshi Z, Temple R, et al. Two metres or one: what is the evidence for physical distancing in covid-19?. . BMJ 2020;370:m3223
2. Stevenson A. Oxford Dictionary of English. Third edition ed. Oxford: Oxford University Press 2010.
3. World Health Organization, editor. WHO Housing and health guidelines. Geneva: Licence: CC BY-NC-SA 3.0 IGO., 2018.
4. U.S. Department of Housing and Urban Development Office of Policy Development and Research. Measuring Overcrowding in Housing. Bethesda: Econometrica, Inc. 2007.
5. Zheng L, Hensher D. Crowding in Public Transport: A Review of Objective and Subjective Measures. Journal of Public Transportation 2013;16(2):107-34.
6. Ganau M, Netuka D, Broekman M, et al. Neurosurgeons and the fight with COVID-19: a position statement from the EANS Individual Membership Committee. Acta Neurochir (2020). https://doi.org/10.1007/s00701-020-04360-3. 2020

Yours sincerely,

Assoc. Prof. Naci Balak, MD, IFAANS
Department of Neurosurgery, Istanbul Medeniyet University, Göztepe Education and Research Hospital,
Kadiköy, Istanbul, Turkey

Competing interests: No competing interests

30 August 2020
Naci Balak
Neurosurgeon
None
Department of Neurosurgery, Istanbul Medeniyet University, Göztepe Education and Research Hospital
Department of Neurosurgery, Istanbul Medeniyet University, Göztepe Education and Research Hospital, Kadıköy, Istanbul, Turkey