Demographic shift in COVID-19 patients in Singapore from an aged, at-risk population to young, migrant workers with reduced risk of severe disease

Ngiam, Jinghao Nicholas; Chew, Nicholas; Tham, Sai Meng; Beh, Darius Lian-Lian; Lim, Zhen Yu; Li, Tony Y.W.; Cen, Shuyun; Tambyah, Paul Anantharajah; Santosa, Amelia; Sia, Ching-Hui; Cross, Gail Brenda

OBJECTIVES: The vast majority of COVID-19 cases in Singapore occurred amongst migrant workers. We examined trends in the hospitalised cases and tested the assumption that the low severity of disease had been related to the relatively young population affected. METHODS: All patients with PCR-positive SARS-CoV-2 admitted from February to April 2020 were divided into: i) imported cases, ii) locally-transmitted cases outside migrant worker dormitories and iii) migrant worker dormitory cases, and were examined for underlying comorbidities, clinical progress and outcomes. RESULTS: Imported cases (n = 29) peaked in mid-March 2020, followed by local cases (n = 100) in mid-April 2020; migrant worker cases (n = 425) continued to increase in late April 2020. Migrant worker cases were younger, with few medical comorbidities, and had less severe disease. As the migrant worker cases increased, the proportion of patients with pneumonia decreased, whilst patients presenting earlier in their illness and asymptomatic disease became more common. CONCLUSION: Singapore experienced a substantial shift in the population at risk of severe COVID-19. Successful control in the community protected an aging population. Large migrant worker dormitory outbreaks occurred, but the disease incurred was less severe, resulting in Singapore having one of the lowest case fatality rates in the world.