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Figure.  Overall Disease Severity Spectrum of Severe Acute Respiratory Syndrome Coronavirus 2 in Migrant Workers in Dormitories in Singapore
Overall Disease Severity Spectrum of Severe Acute Respiratory Syndrome Coronavirus 2 in Migrant Workers in Dormitories in Singapore

ICU indicates intensive care unit. The death was determined to be coronavirus disease 2019 (COVID-19) related. Data outside of pyramid are rates calculated using standard binomial formulas. Of the 111 280 patients with COVID-19, 1 died (0.0009%) (vs 0.004% of all clinical cases).

Table.  Laboratory Tests and Severe Acute Respiratory Syndrome Coronavirus 2 Infection Status of Migrant Workers Residing in Singapore’s Purpose-Built Dormitories (March 25 to July 25, 2020)
Laboratory Tests and Severe Acute Respiratory Syndrome Coronavirus 2 Infection Status of Migrant Workers Residing in Singapore’s Purpose-Built Dormitories (March 25 to July 25, 2020)
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Yi  H, Ng  ST, Farwin  A, Low  PTA, Chang  CM, Lim  J.  Health equity considerations in COVID-19: geospatial network analysis of the COVID-19 outbreak in the migrant population in Singapore.   J Travel Med. Published online September 7, 2020. doi:10.1093/jtm/taaa159PubMedGoogle Scholar
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Lisboa Bastos  M, Tavaziva  G, Abidi  SK,  et al.  Diagnostic accuracy of serological tests for COVID-19: systematic review and meta-analysis.   BMJ. 2020;370:m2516. doi:10.1136/bmj.m2516PubMedGoogle ScholarCrossref
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Research Letter
February 9, 2021

Prevalence and Outcomes of SARS-CoV-2 Infection Among Migrant Workers in Singapore

Author Affiliations
  • 1Department of Medical Oncology, National Cancer Centre Singapore, Singapore
  • 2Ministry of Health, Singapore
  • 3Headquarters Medical Corps, Singapore Armed Forces Headquarters, Singapore
  • 4Saw Swee Hock School of Public Health, National University of Singapore, Singapore
  • 5Department of Medicine, National University Singapore, Singapore
  • 6Dental Services, Tan Tock Seng Hospital, Singapore
JAMA. 2021;325(6):584-585. doi:10.1001/jama.2020.24071

High-density communal residences are at elevated risk of large outbreaks of respiratory disease.1,2 After an initial nationwide outbreak of 231 cases of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections in Singapore, which was contained as of March 24, 2020, a surge of 244 cases among migrant workers residing in dormitories, largely from Bangladesh and India, occurred from March 25 to April 7. A national task force was formed to coordinate Singapore’s outbreak response. A national lockdown from April 7 to June 1 enforced movement restriction and confined workers to their dormitories. Medical posts were deployed on-site in all dormitories, and testing capacity for testing and screening residents increased. All workers with a positive polymerase chain reaction (PCR) test result were admitted to health care facilities for isolation and treatment. We examined the prevalence and outcomes of SARS-CoV-2 infection among migrant workers in Singapore.

Methods

Migrant workers residing in all purpose-built dormitories in Singapore between March 25 and July 25, 2020, were included. Residents who presented with symptoms for medical consultation had nasopharyngeal swabs tested by PCR. Serology on blood samples was also performed for clinical evaluation in selected cases with commercially available kits from Siemens, Abbott, or Roche.3 Screening with PCR was performed in exposed residents, those with medical conditions, and those living in close contact with clustered outbreaks. Toward the end of the outbreak, beginning May 23, testing was performed to determine the status of all residents not previously known to be infected, using a combination of serology and/or PCR, with serology performed in heavily infected dormitories and PCR in less-infected dormitories. Clinical cases were defined as those who presented with symptoms for medical consultation, while subclinical cases were infections found during mass screening among residents without presentation for medical consultation (including workers who never presented for medical consultation or previously symptomatic workers with prior negative test results).

This study was sanctioned by the Singapore Ministry of Health Infectious Disease Act and exempted from institutional review board review because it was conducted as a part of the national public health response to the emerging coronavirus disease 2019 (COVID-19) pandemic. The data were obtained through centralized government databases, including clinical case counts, intensive care unit (ICU) admissions, COVID-19–related mortality data, and laboratory results. Statistical analysis (calculation of rates and 95% CIs) was performed using R version 4.0.0.4

Results

There were 43 dormitories housing 198 320 migrant workers with a median occupancy of 3578 (interquartile range, 1458-6120); 99.8% of residents were male, with a median age of 33 years (interquartile range, 28-39 years). As of July 25, 95.1% of all residents had at least 1 SARS-CoV-2 test, including 63.6% with PCR and 68.4% with serology. There were 111 280 residents with a positive PCR or serology result, for an overall infection prevalence of 56.1% (95% CI, 55.9%-56.3%) (range per dormitory, 0%-74.7%; median, 52.9%) (Figure). There were 24 197 clinical cases (12.2% of all residents; 21.7% of infected) from 42 dormitories and 87 083 subclinical cases (43.9% of all residents; 78.3% of all infected) (Table). Of all clinical cases, 20 cases required ICU admission (0.08% [95% CI, 0.05%-0.13%]), with 1 COVID-19–attributable death (case-fatality rate, 0.004% [95% CI, 0.0002%-0.027%]).

Discussion

The COVID-19 outbreak among Singapore’s migrant workers was characterized by a high prevalence of infection, low morbidity with few ICU admissions, and low mortality. The low case-fatality rate compares favorably with rates reported in other national registries.5,6 Although migrant workers are younger and generally healthy, the nationally coordinated public health response and clinical care for all cases likely contributed to favorable health outcomes. The infection prevalence would have been severely underestimated if only persons presenting for medical consultation were tested because most infections were subclinical and were identified through mass screening.

Limitations of the study include that some subclinical cases with mild symptoms may have been miscategorized, and incomplete sensitivity of laboratory tests may also have led to an underestimate of prevalence.

Section Editor: Jody W. Zylke, MD, Deputy Editor.
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Article Information

Accepted for Publication: November 16, 2020.

Corresponding Author: Vernon J. Lee, MBBS, PhD, Communicable Diseases Division, Ministry of Health Singapore, College of Medicine Bldg, 16 College Rd, Singapore 169854 (vernon_lee@moh.gov.sg).

Author Contributions: Drs I. B. Tan and Cook had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.

Concept and design: I. B. Tan, C. Tan, Dan, Lee.

Acquisition, analysis, or interpretation of data: All authors.

Drafting of the manuscript: I. B. Tan, C. Tan, Hsu, Dan, Cook, Lee.

Critical revision of the manuscript for important intellectual content: I. B. Tan, C. Tan, Hsu, Dan, Aw, Lee.

Statistical analysis: I. B. Tan, C. Tan, Cook.

Obtained funding: I. B. Tan.

Administrative, technical, or material support: C. Tan, Hsu, Dan, Aw.

Supervision: Dan, Aw, Lee.

Conflict of Interest Disclosures: Dr Dan reported receiving personal fees from the Novartis advisory board, Boehringer Ingelheim, and Gilead and conference sponsorship from AbbVie. No other disclosures were reported.

Funding/Support: Drs I. B. Tan and Cook received research support from the National Medical Research Council.

Role of the Funder/Sponsor: The funder had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.

Additional Contributions: We thank Jeremy Teoh, MBBS, Muhammad Taufeeq Wahab, MBBS (Singapore Armed Forces), and Pui-Mun Wong, PhD (Genome Institute of Singapore), for analysis and manuscript drafting. We thank Kelvin Bryan Tan, PhD, Ganga Ganesan, MSc, Deanette Pang, BSocSci, Tessa Randini, PhD, Rachael Pung, MSc, Zheng Yi Lau, MSc (Ministry of Health, Singapore), and Christine Loan Ping Eng, PhD (Genome Institute of Singapore), for assisting with data collation and database management. We thank Benjamin Kian Chung Ong, MBBS, Derrick Heng, MPH, and Kenneth S. W. Mak, MBBS (Ministry of Health, Singapore), for development of public health management and testing policies and plans and Steven Tien Guan Thng, MBBS (National Skin Centre, Singapore), Alexander W. Gorny, MBBS, MSc (Ministry of Health), Lionel Tim-Ee Chen, MBBS, MMed, Hee Nee Pang, MBBS, Biauw Chi Ong, MBBS, MMed (SingHealth), Guan Lin Lee, MBBS, Kai Xiong Cheong, MBBS, Joachim Wen Kien Yau, MBBS (Singapore Armed Forces), Ying Jang Mok, MBBS, Darren E. J. Seah, MMed (National Healthcare Group, Singapore), Dale Fisher, MBBS, Yee Sin Leo, MBBS, MPH, Thomas Loh, MBBS (National University Health System, Singapore), Bee Hoon Heng, MSc (National Healthcare Group Singapore), and Edwin C. T. Low, MBBS (Singapore Health Services), for implementation of public health management and conduct of mass screening and Wei Yee Wan, MBBS (SingHealth), Raymond T. P. Lin, MBBS, and Sunil Sethi, MBBS, MMed (National University Health System, Singapore), for performing laboratory analyses. No compensation was received for their contributions to this work.

References
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Sloane  PD.  Cruise ships, nursing homes, and prisons as COVID-19 epicenters: a “wicked problem” with breakthrough solutions?   J Am Med Dir Assoc. 2020;21(7):958-961. doi:10.1016/j.jamda.2020.04.020PubMedGoogle ScholarCrossref
2.
Yi  H, Ng  ST, Farwin  A, Low  PTA, Chang  CM, Lim  J.  Health equity considerations in COVID-19: geospatial network analysis of the COVID-19 outbreak in the migrant population in Singapore.   J Travel Med. Published online September 7, 2020. doi:10.1093/jtm/taaa159PubMedGoogle Scholar
3.
Lisboa Bastos  M, Tavaziva  G, Abidi  SK,  et al.  Diagnostic accuracy of serological tests for COVID-19: systematic review and meta-analysis.   BMJ. 2020;370:m2516. doi:10.1136/bmj.m2516PubMedGoogle ScholarCrossref
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R Core Team. R: A Language and Environment for Statistical Computing. Accessed June 1, 2020. https://www.R-project.org/
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World Health Organization. WHO coronavirus disease (COVID-19) dashboard. Accessed July 19, 2020. https://covid19.who.int/
6.
European Centre for Disease Prevention and Control. COVID-19 surveillance report. Accessed July 19, 2020. https://covid19-surveillance-report.ecdc.europa.eu/
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