Bagdasarian and Fisher BMC Medicine(2020) 18:164
https://doi.org/10.1186/s12916-020-01625-7

COMMENTARYOpen Access

Heterogenous COVID-19 transmission
dynamics within Singapore: a clearer
picture of future national responses
N. Bagdasarian1,2*

and D. Fisher1,2

Keywords: COVID-19, Transmission dynamics

BackgroundIn their paper entitled “Real-time monitoring the transmission potential of coronavirus disease 2019 (COVID19) in Singapore, March 2020”, Tariq and colleagues
utilise publicly available data published by the Singapore
Ministry of Health to estimate the effective reproduction
number (Rt) of COVID-19 in Singapore [1]. The authors
evaluate each linked cluster of cases, study transmission
chains and take into account estimates of reporting delays. They use this information to calculate an Rt of lessthan 1.0 and conclude that estimates for Singapore aresubstantially lower than those reported in other parts of
the world due to robust containment efforts inSingapore. The authors point to super-spreader eventsand asymptomatic shedding as major drivers of transmission heterogeneity in countries like Singapore andSouth Korea and conclude that maintaining social distancing and active case finding are key to “stomp [sic]out all active or incoming chains of transmission”. However, it is important to centre this analysis in the current
situation in Singapore. We must stress that, while theauthors’ conclusions are accurate, they do not accountfor the recent transmission dynamics experienced inSingapore.
This comment refers to the article available at https://doi.org/10.1186/
s12916-020-01615-9.
* Correspondence: natasha_bagdasarian@nuhs.edu.sg
1
Department of Medicine, University Medicine Cluster, National University
Hospital, Singapore, Singapore
2
Department of Medicine, Yong Loo Lin School of Medicine, National
University of Singapore, Singapore, Singapore

The current situation in Singapore
As of this writing (May 8, 2020), Singapore has had over
20,000 cases of COVID-19, with recent growth rates
reaching over 1300 new cases per day [2]. This growthhas been predominantly driven by cases coming from
migrant workers, living in large, population-dense facilities [2]. More than 20% of Singapore’s population of 5.7
million are foreign workers, and the majority are manual
workers from Bangladesh and India, working in construction, shipping, manufacturing and domestic service
sectors [3]. Many live in massive dormitory facilities,
with the largest having a capacity of 25,000 residents ina single compound, and up to 20 residents sharing aroom, with communal bathroom, dining and recreation
facilities [3]. This type of crowding provides a very vulnerable setting for infectious disease outbreaks, and theextent of this is now being realised in Singapore, with almost all the recent reported cases of COVID-19 (> 95%)
reported from the dormitories [2].
Multiple outbreaks taking place simultaneously
While the results of the analysis by Tariq et al. are important, the recent developments in Singapore highlightthe fact that heterogeneity in an outbreak is not just apossibility, but an inevitability. It appears at first glancethat Singapore is experiencing three outbreaks, which
can be confirmed by Singapore Ministry of Health data
[2] and demonstrated by multiple distinct epidemiccurves. The first was an epidemic of imported cases thatpeaked on March 23rd with less than 50 cases per day;this epidemic curve was abruptly halted by travel© The Author(s). 2020 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License,
which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give
appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate ifchanges were made. The images or other third party material in this article are included in the article's Creative Commonslicence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commonslicence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain
permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to thedata made available in this article, unless otherwise stated in a credit line to the data.

Bagdasarian and Fisher BMC Medicine(2020) 18:164

restrictions for short-term visitors [4]. Next came an epidemic curve of community cases that peaked on April
8th with less than 60 cases reported per day; this curve
saw a sharp decline after a nationwide “circuit breaker”
was announced, which closed all non-essential businesses and included social distancing mandates and restrictions on social gatherings, as well as strict penalties
for those not complying [5].
However, travel restrictions and social distancing mandates did nothing to prevent a new epidemic of COVID19 cases from the dormitories, which ballooned just as
the strict “circuit breaker” measures were introduced on
April 7th, and which peaked on April 20th with 1371
cases from the dormitories reported in a single day [2].
Even this idea of three separate epidemics in Singapore
does not tell the whole story. The dormitories themselves are heterogeneous, with each dormitory, eachbuilding and each floor undergoing its own small epidemic and revealing its own specific transmission dynamics. Countries will increasingly see that epidemic
curves, reproduction numbers and outbreak interventions will vary between contexts within a country.
In the COVID-19 pandemic, heterogeneity in transmission patterns are not the exception, they are the rule, andwe will soon see this increasingly identified across theworld. Communities may manage to reduce transmission
by asking residents to stay at home and comply with social
distancing measures, but broadly implemented interventions will not be effective or practical in many settings.
COVID-19 outbreaks in the USA in prisons [6] and nursing homes [7] and some highly publicised outbreaks oninternational cruise ships [8] have already shown us thatasymptomatic viral shedding may be the major driver oftransmission in crowded conditions where social distancing is not a practical intervention. Outbreaks in threeclusters are driving Australian figures even during theirlockdown: a hospital in Tasmania, an abattoir in Victoria
and a nursing Home in New South Wales [9].
Transmission dynamics and containment strategies
will look very different in selected settings, and this cannot be seen any more clearly than in facilities housing
hundreds or thousands of individuals. Community engagement and other public health measures will need tobe targeted and adaptable to the needs of these settings.
Singapore’s case and contact finding measures pairedwith isolation and quarantine were extremely effective at
stopping community spread. The same principles are
now being adapted and tailored to fit the needs of thedormitory residents, their living circumstances and thescale of the issue.

Conclusions
The blunt COVID-19 figures reported across the globe
represent complex and disparate transmission dynamics

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in different settings, which require real-world epidemiological understanding and tailored outbreak response
strategies. In Singapore, the numbers of COVID-19 casesbeing reported from the dormitories appear to be levelling off [2], and with mobilisation of medical care onsite,
isolation facilities and massive screening exercises, adownward trend seems to be within sight.
Migrant workers around the world have been among
the most vulnerable groups affected by the pandemic[10, 11]. The transparency offered by Singapore, and thepublicly available data which allowed Tariq et al. tocomplete their analysis, may now provide a blueprint foreffectively adapting COVID-19 containment strategies inorder to protect some of our most vulnerable populations around the globe.
Abbreviations
COVID-19: Coronavirus disease 2019; Rt: Effective reproduction number
Acknowledgements
Not applicable
Authors’ contributions
NB contributed to writing and editing; DF contributed to writing andediting. The authors read and approved the final manuscript.
Funding
None
Availability of data and materials
Not applicable
Ethics approval and consent to participate
Not applicable
Consent for publication
Not applicableCompeting interests
DF is a Board Member on the Journal. The other author declares that they
have no competing interests.
Received: 11 May 2020 Accepted: 11 May 2020References
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4. COVID-19: Travel restrictions for foreign visitors entering Singapore. http://www.gov.sg/article/covid-19-travel-restrictions-for-foreign-visitors-enteringsingapore.
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