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Continued demographic shifts in hospitalised patients with COVID-19 from migrant workers to a vulnerable and more elderly local population at risk of severe disease
Department of Cardiology, National University Heart Centre Singapore, SingaporeDepartment of Medicine, Yong Loo Lin School of Medicine, National University of Singapore, Singapore
Department of Infectious Diseases, National University Health System, SingaporeDepartment of Medicine, Yong Loo Lin School of Medicine, National University of Singapore, Singapore
Department of Cardiology, National University Heart Centre Singapore, SingaporeDepartment of Medicine, Yong Loo Lin School of Medicine, National University of Singapore, SingaporeInfectious Diseases Translational Research Programme, Department of Medicine, Yong Loo Lin School of Medicine, National University of Singapore
In 2020, COVID-19 predominantly affected young migrant workers in Singapore.
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Therefore, a low incidence of severe complications was observed in 2020.
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In 2021, COVID-19 affected Singapore's more elderly and vulnerable local population.
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Consequently, there was a greater strain on intensive care facilities in 2021.
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Monitoring COVID-19 demographic shifts help guide healthcare resource allocation.
Abstract
Objectives: In the early months of the COVID-19 pandemic in Singapore, the vast majority of infected persons were migrant workers living in dormitories who had few medical comorbidities. In 2021, with the Delta and Omicron waves, this shifted to the more vulnerable, elderly population within the local community. We examined evolving trends among the hospitalised cases of COVID-19.
Methods: All patients with polymerase chain reaction-positive SARS-CoV-2 admitted from February 2020 to October 2021 were included and subsequently stratified by their year of admission (2020 or 2021). We compared the baseline clinical characteristics, clinical course, and outcomes.
Results: A majority of cases were seen in 2020 (n = 1359), compared with 2021 (n = 422), due to the large outbreaks in migrant worker dormitories. Nevertheless, the greater proportion of locally transmitted cases outside of dormitories in 2021 (78.7% vs 12.3%) meant a significantly older population with more medical comorbidities had COVID-19. This led to an observably higher proportion of patients with severe disease presenting with raised inflammatory markers, need for therapeutics, supplemental oxygenation, and higher mortality.
Conclusion: Changing demographics and the characteristics of the exposed populations are associated with distinct differences in clinical presentation and outcomes. Older age remained consistently associated with adverse outcomes.
In a previous study, we examined the first 3 months of the pandemic and the shifting demographics of hospitalised patients with COVID-19 in Singapore [
]. This subsequently led to a small outbreak within the local community, which was rapidly curbed by aggressive case-finding and quarantining of the affected cases and their contacts (Ministry of Health [[
However, although these measures had been effective in limiting the cases within the local community, migrant workers in dormitories with crowded living conditions were not spared [
]. This large and sustained outbreak in the migrant worker dormitories accounted for the vast majority of hospitalised patients with COVID-19 in Singapore in 2020 [
]. These migrant workers tended to be young and fit men with few medical comorbidities. As such, they were at low risk for progression to severe COVID-19 or developing life-threatening complications of the disease [
]. Indeed, at that time, due to the active case-finding (a “zero-COVID” approach) and the relatively young and low-risk affected population, Singapore reported among the lowest mortality rates for COVID-19 in the world [
Evaluating rates and determinants of COVID-19 vaccine hesitancy for adults and children in the Singapore population: strengthening our community's resilience against threats from emerging infections (Socrates) cohort.
]pore] 2021). In addition, the rapid spread of the Delta variant in the third quarter of 2021 raised the concern of overcrowding in healthcare facilities; thus, in comparison to 2020, in 2021, persons with COVID-19 were no longer routinely quarantined in a hospital or care facilities but were allowed to recover at home. People with COVID-19 were, however, required to be hospitalised if they had risk factors for disease progression, such as if they were unvaccinated and/or were more vulnerable to severe disease despite vaccination on account of comorbidities or age. In this study, we described the changing trends in hospitalised patients with COVID-19 as the pandemic progressed in Singapore from 2020 to 2021.
2. Methods
We retrospectively examined patients consecutively admitted between February 2020 to October 2021 at a single tertiary academic institution in Singapore who had polymerase chain reaction (PCR)-proven COVID-19. Patients who were less than 21 years of age were excluded from this study, as were patients who did not require hospital admission or who were cared for only in community care facilities.
The study population was divided based on their admission year (2020 or 2021) and subsequently also stratified by age category (<40 years or ≥40 years of age). For each patient, we collected information on their demographic background, clinical presentation, laboratory findings, and other investigations conducted within 24 hours of hospital admission. The progress of each patient was followed, including the use of COVID-19-specific therapeutics (such as remdesivir, dexamethasone, baricitinib, or tocilizumab) and clinical outcomes, such as the presence of pneumonia, need for supplemental oxygen, transfer to intensive care, and in-hospital mortality.
To compare differences in characteristics between those admitted in 2020 compared with 2021, t-tests were used for continuous variables, while chi-squared tests were used for categorical variables. Data for continuous variables were expressed as means (± 1 SD), while data for categorical variables were expressed as frequencies (and percentages). A P-value of less than 0.05 was considered significant in this study. All data analyses were performed on SPSS version 20.0 (SPSS, Inc., Chicago, Illinois). This study was approved by the National Healthcare Group Domain Specific Review Board (DSRB 2020/00545). The study was conducted in line with the principles laid out by the Declaration of Helsinki. All data were anonymised, and a waiver of written informed consent was obtained before the conduct of the study.
3. Results
A total of 1781 patients required hospital admission for COVID-19 between February 2020 to October 2021. A total of 1359 patients with COVID-19 were admitted in 2020 and 422 in 2021. The mean age of those admitted in 2021 was 60.0 years compared with 39.4 years in 2020 (P <0.001). Dormitory workers accounted for the majority of the outbreak in 2020, compared with 2021 (83.7% vs 4.0%, P <0.001), with men correspondingly accounting for a much larger proportion in 2020 compared with 2021 (90.8% vs 46.2%, P <0.001) (Table 1). The outbreak in Singapore began with a few cases among returning travellers from February to March 2020, followed by small clusters within the community in April 2020. Alongside the outbreak in the community outside the dormitories, which was brought under control quickly, there was a large, uncontrolled outbreak in migrant worker dormitories, which peaked in May 2020 and only subsided substantially in August 2020. Between August 2020 and the new year, there was little transmission within the dormitories or within the community at large in Singapore despite the loosening of social distancing restrictions. However, once again, in early 2021, with the advent of the Delta variant of concern, a few cases in returning travellers gradually built to a relatively large outbreak of cases among the local population in Singapore, which initially peaked around mid-September 2021 (Figure 1).
Table 1Demographic shifts in the clinical characteristics of patients admitted with COVID-19 from 2020 to 2021 in a tertiary academic hospital in Singapore.
Figure 1Transmission of COVID-19 cases in Singapore over time, comparing local (community) cases with returning travellers (overseas) and migrant worker (dormitory) cases.
Patients admitted in 2021 had a greater likelihood of having medical comorbidities such as hypertension, diabetes mellitus, and chronic kidney disease. A total of 59.5% had no previous medical conditions in 2021, compared with 84.5% in 2020. Asymptomatic disease was more common among hospitalised patients in 2020 (18.5%) compared with 2021 (13.0%) (Table 1). Those above and below 40 years of age had a comparable prevalence of asymptomatic disease (Table 2). Despite good uptake of the COVID-19 vaccines in the community in Singapore since early 2021 (64.7% of the admitted COVID-19 cases in 2021 had received at least one dose of the vaccination), symptoms of acute respiratory illness (e.g., cough, rhinorrhoea, sore throat) were far more common in 2021 (80.3% vs 60.9%, P <0.001) probably related to the public health policies which did not mandate admission to a hospital or community care facility for all patients who were SARS-CoV-2 positive by PCR in 2021. Anosmia was slightly more common in 2020 compared with 2021 (5.9% vs 3.3%, P-value = 0.045) (Table 1). Older patients (>40 years of age) had a similar prevalence of anosmia compared with their younger counterparts (Table 2). Oxygen saturation at presentation in 2021 was marginally lower compared with 2020 (97.6 ± 3.0 vs 98.0 ± 2.0%, P-value = 0.003), but no significant differences in the duration of fever were found (Table 1). When stratified by age, older patients (>40 years of age) tended to have more persistent fever and marginally lower oxygen saturations at presentation (Table 2).
Table 2Clinical characteristics of patients admitted with COVID-19 from 2020 to 2021 in a tertiary academic hospital in Singapore, stratified by year of admission and age category.
Patients in 2021 were more likely to present with lower lymphocyte count (1.48 ± 0.74 vs 2.00 ± 1.45 × 109/l, P <0.001), higher C-reactive protein concentrations (23.1 ± 38.0 vs 12.5 ± 26.4 mg/dl, P <0.001), and higher serum ferritin concentrations (254.1 ± 444.7 vs 196.1 ± 233.5 µg/l, P-value = 0.001) (Table 1). Older patients (>40 years of age) across both the years of the study consistently had higher levels of C-reactive protein and serum ferritin levels compared with their younger counterparts (Table 2). In 2021, a greater proportion of patients received COVID-19-specific drugs than in 2020, including dexamethasone (11.1% vs 0.7%, P <0.001), remdesivir (11.1% vs 2.9%, P <0.001), and baricitinib (1.2% vs 0.3%, P-value = 0.039). Sotrovimab, a neutralising monoclonal antibody, was also only available in Singapore in 2021, and 16 patients (3.8%) of the cohort in 2021 received this medication (Table 1). Similarly, across both the years of study, older patients (>40 years of age) were more likely to receive COVID-19-specific therapeutics than those that were younger (Table 2).
No difference in the length of hospital stay was found between the two study periods (7.8 ± 9.1 days in 2020 and 7.4 ± 7.9 days in 2021, P-value = 0.356) mainly because discharge policies changed in tandem with admission policies, meaning that in 2021, patients were not kept in hospital until they had tested negative for COVID-19 on PCR. As shown in Figure 2, Figure 3, the proportion of cases who had pneumonia and required intensive care fell dramatically in 2020 and then rose again in June 2021 when the vulnerable, elderly population were once again exposed to COVID-19 (Figures 2 and 3) A higher proportion of patients required supplemental oxygenation in 2021 (10.9%) compared with 2020 (2.9%, P <0.001), and there was higher mortality among those admitted in 2021 (1.9% vs 0.4%, P-value = 0.004). Across both years of study, older patients consistently had a higher proportion of patients with adverse outcomes, such as requiring supplemental oxygenation, intensive care, and death (Table 2).
Figure 2Percentage of hospitalised COVID-19 patients with pneumonia over time.
In this retrospective analysis of the first 1781 patients admitted with COVID-19 to our hospital between February 2020 to October 2021, we examined the differences in the patient profile between those admitted in the year 2020 compared with those admitted in 2021. The key findings were that (i) the outbreak in 2020 encompassed predominantly a young migrant worker population, whereas, in 2021, the patient profile was largely elderly patients from the community with comorbidities; (ii) patients were significantly more unwell in 2021 with a higher proportion of pneumonia, severe disease at presentation, higher inflammatory markers, and a greater prevalence in the use of COVID-19-specific drugs; and (iii) that despite the availability of effective COVID-19 therapeutics and effective vaccination in 2021 (where 64% of the hospitalised cohort in 2021 had received at least one dose of the vaccine, and 54.5% had two or more doses of vaccination), there remained a higher proportion of patients with adverse outcomes, including mortality, among the hospitalised cohort. Furthermore, another consistent finding was that despite the changes in the circulating virus strains, and introduction of COVID-19-specific therapeutics and effective vaccination across the years, we consistently found that (iv) older age was uniformly associated with more severe illness and adverse clinical outcomes among those hospitalised with COVID-19.
A broad overview of the changes to the community measures implemented and COVID-19 management in response to the pandemic from 2020 to 2021 is summarised in Table 3. Our study demonstrated that COVID-19 patients who were younger and had fewer medical comorbidities appeared to be protected against the development of moderate to severe disease, even if infected with the original Wuhan strain or in the absence of vaccination. This original Wuhan strain had been associated with much higher overall excess mortality in Europe and North America [
National Centre for Infectious Diseases Singapore. Treatment Guidelines for COVID-19. https://www.ncid.sg/Health-Professionals/Diseases-and-Conditions/Pages/COVID-19.aspx (accessed 02 April 2022)
January - March 2020
23 January 2020: First case of COVID-19 diagnosed in Singapore 4 February 2020: First case of local transmission in Singapore 7 February 2020: DORSCON Orange 20 March 2020: Launch of contact-tracing app
All COVID-19 patients admitted to tertiary hospitals for initial evaluation and monitoring, then subsequently discharged to community facilities for further isolation
April - June 2020
4 April 2020: Several clusters identified in migrant worker dormitories 7 April 2020: “Circuit-breaker” measure start in the community 9 April 2020: “Stay-home notices” for returning travellers from all countries 1 June 2020: Phase 1 of Singapore's reopening (end of circuit-breaker measures) 19 June 2020: Phase 2 of Singapore's reopening
2 April 2020: NCID Singapore releases Interim Treatment Guidelines for COVID-19 (version 1.0) 10 April 2020: Large community isolation facility opens in the Expo to isolate COVID-19 patients during the recovery period 10 June 2020: Remdesivir approved for use in COVID-19 treatment in Singapore by the Health Sciences Authority 16 June 2020: Preliminary results of RECOVERY trial announced - Dexamethasone for the use in COVID-19
June - December 2020
28 December 2020: Phase 3 of Singapore's reopening
30 December 2020: Start of the COVID-19 vaccination campaign
January - June 2021
8 May 2021: Back to phase 2 measures due to rise in cases from the Delta variant 16 May 2021: Back to phase 2 heightened alert measures 14 June 2021: Phase 3 heightened alert measures
4 January 2021: Baricitinib recommended for severe COVID-19 as part of the NCID Interim Treatment Guidelines (version 5.0) 14 June 2021: Tocilizumab recommended for severe COVID-19 as part of the NCID Interim Treatment Guidelines (version 6.0) 30 June 2021: Sotrovimab receives interim authorisation in Singapore from the Health Sciences Authority
July - December 2021
22 July 2021: Return to phase 2 (heightened alert) measures to curb COVID-19 13 October 2021: Vaccination-differentiated measures implemented (e.g., only fully vaccinated individuals may enter shopping malls)
29 August 2021: 80% of the population is vaccinated against COVID-19 14 September 2021: COVID-19 booster vaccination for senior citizens above 60 years of age 10 October 2021: Home recovery programme is the default for most of the population
Besides patient-related factors, differences seen between the two study periods were also likely to be due to a change in public health policy: in 2020, all COVID-19 patients were required to be isolated in a care facility or hospital, while in 2021, patients with COVID-19 were instead encouraged to recover at home (Ministry of Health [[
]pore] 2022). Only those deemed to be at greater risk of moderate to severe disease were hospitalised, namely those who were not vaccinated, partially vaccinated, who were in an older age category, or who had medical comorbidities, reflective of the demographic change we saw in our inpatient cohort in 2021. This meant that the hospitalised cohort was more selected and reflected only those at risk of more severe disease and progression, placing a significant burden on intensive care facilities in 2021 [
Additionally, the circulating viral strain was also likely to have differed across these two periods: the Delta variant was the predominant strain in Singapore in 2021 compared with the original Wuhan strain, which affected the majority of the migrant worker population in Singapore in 2020 [
]. The Delta variant was associated with increased transmissibility and was reported to have more pneumonia compared with the original Wuhan strain, which may have impacted our findings [
]. It was difficult to tease out the relative contribution of vaccination uptake, the changes in strain, and the changes in demographics on the outcomes of hospitalised patients with COVID-19. All these factors were likely to have contributed to the observed changes in the clinical profile and patient outcomes. However, the consistent age-related differences in mortality in both years in our cohort suggest that demographics played a major contributing role in outcomes.
Finally, the increase in the use of COVID-19-specific therapeutics would likely also have been related to better-established international guidelines on COVID-19 management and increasing global experience in the efficacy and safety of these therapeutic agents [
]. These guidelines were first released on April 02, 2020 and updated over the years to guide the use and improve the uptake of COVID-19-specific therapeutics in Singapore, such as remdesivir, dexamethasone, sotrovimab, tocilizumab, and baricitinib, where clinically indicated. The higher uptake of COVID-19-specific therapeutics within the hospitalised cohort in 2021 compared with 2020 may reflect the more severe disease in this population, but improved knowledge and confidence in their use, together with the established treatment guidelines, may also have been contributory.
Several countries in Asia had also adopted a strict containment strategy for COVID-19 early in the pandemic. For example, South Korea and China both rapidly enforced strategies early in the pandemic in 2020 to test, contact trace, and treat cases of COVID-19 [
] together with quarantine for contacts and various social distancing measures. Other similar strategies included enforcing border controls and restricting entry into the country in 2020 [
]. Several countries, including Singapore, shifted towards aiming to effectively vaccinate and protect their vulnerable population against COVID-19 while easing other restrictions as economies and global trade began to recover [
]. In most countries, similar “waves” of cases of COVID-19 were observed, which each new circulating variant of the virus. With its highly vaccinated population, although the hospitalised cohort appeared more ill in 2021 compared with 2020, Singapore continued to observe relatively low mortality rates among patients infected with COVID-19. Indeed, these patterns have also been seen in other countries with high vaccination rates [
As the pandemic situation continues to evolve in Singapore, as it does around the world, accurate interpretation of clinical case data is critically important. With changes in public health policies at every jurisdiction and the discovery of new variants against which vaccines, monoclonal antibodies, and antiviral agents may have reduced efficacy, we will no doubt continue to field new challenges in managing COVID-19 and discovering how it impacts various sectors in our communities.
5. Limitations
This was a retrospective single-centre cohort of patients hospitalised with COVID-19. It was a heterogeneous cohort of patients, given that not all patients required hospital admission because they had been clinically unwell or were at significant risk of deterioration. In the clinical context, early in the pandemic, patients had also been admitted for the purpose of isolation and triage before subsequent transfer to isolation facilities within the community. Our study was observational and retrospective in design. We did not capture or examine the cases that were managed directly in these community facilities or who recovered at home, which formed the bulk of the COVID-19 cases in Singapore from 2020 to 2021. The observed differences in trends and outcomes among hospitalised patients with COVID-19 may be a result of a combination of factors, including the changes in circulating viral strain, changes in public health policy (for example, only admitting severely ill patients to the hospital) in addition to the changes in the demographics of the affected population, which we highlighted. Our study had not been designed to estimate the effect size of each factor on the changes in the observed trends and outcomes. Nevertheless, we believe that this snapshot of hospitalised patients gives valuable insight into the profile of hospitalised patients over time and their evolving needs.
6. Conclusion
In conclusion, the demographics of individuals affected by COVID-19 in Singapore shifted dramatically from 2020 to 2021. Despite high vaccination uptake rates against COVID-19, the disease has shifted from a predominantly young and low-risk migrant worker population to affect the more vulnerable local community in 2021, with hospitalised patients consequently being more ill and having a greater need for intensive care and higher mortality. With the benefit of hindsight, it is possible to argue that the zero-COVID strategy, which reduced transmission outside the migrant worker dormitories in 2020, was not sustainable in an open society where there is the constant risk of the introduction of new, more transmissible variants of concern. Despite the changes in the circulating viral strains over the study period and the introduction of effective vaccination against COVID-19 and COVID-19-specific therapeutics, older age remained an important risk factor for more severe disease and adverse clinical outcomes among hospitalised patients with COVID-19 in our centre and elsewhere. Further prospective study is warranted to monitor the shifting demographic trends with new and emerging variants of concerns.
Declarations of competing interest
The authors have no competing interests to declare.
Funding
There was no funding for this study. CHS was supported by the National University of Singapore Yong Loo Lin School of Medicine's Junior Academic Fellowship Scheme.
Ethical approval
This study was approved by the hospital's institutional review board (National Healthcare Group (NHG) Domain Specific Review Board (DSRB) 2020/00545)
Author contributions
JNN, SC, WG, and MYS contributed to the conception, data collection, analysis, and writing of the manuscript. NWSC, CHS, GBC, and PAT contributed to the conception, data analysis, writing, and critical review of the manuscript.
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Demographic shift in COVID-19 patients in Singapore from an aged, at-risk population to young migrant workers with reduced risk of severe disease.
Evaluating rates and determinants of COVID-19 vaccine hesitancy for adults and children in the Singapore population: strengthening our community's resilience against threats from emerging infections (Socrates) cohort.
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