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Importance: Since January 2020, Singapore has implemented comprehensive measures to suppress SARS-CoV-2. Despite this, the country has experienced contrasting epidemics, with limited transmission in the community and explosive outbreaks in migrant worker dormitories. Objective: To estimate SARS-CoV-2 infection incidence among migrant workers and the general population in Singapore. Design: Prospective serological cohort studies. Setting: Two cohort studies — in a migrant worker dormitory and in the general population in Singapore. Participants: 478 residents of a SARS-CoV-2-affected migrant worker dormitory were followed up between May and July 2020, with blood samples collected on recruitment and after 2 and 6 weeks. In addition, 937 community-dwelling adult Singapore residents, for whom pre-pandemic sera were available, were recruited. These individuals also provided a serum sample on recruitment in November/December 2020. Exposure: Exposure to SARS-CoV-2 in a densely populated migrant worker dormitory and in the general population. Main outcomes and measures: The main outcome measures were the incidences of SARS-CoV-2 infection in migrant workers and in the general population, as determined by the detection of neutralizing antibodies against SARS-CoV-2, and adjusting for assay sensitivity and specificity using a Bayesian modeling framework. Results: No evidence of community SARS-CoV-2 exposure was found in Singapore prior to September 2019. It was estimated that < 2 per 1000 adult residents in the community were infected with SARS-CoV-2 in 2020 (cumulative seroprevalence: 0.16%; 95% CrI: 0.008–0.72%). Comparison with comprehensive national case notification data suggested that around 1 in 4 infections in the general population were associated with symptoms. In contrast, in the migrant worker cohort, almost two-thirds had been infected by July 2020 (cumulative seroprevalence: 63.8%; 95% CrI: 57.9–70.3%); no symptoms were reported in almost all of these infections. Conclusions and relevance: Our findings demonstrate that SARS-CoV-2 suppression is possible with strict and rapid implementation of border restrictions, case isolation, contact tracing, quarantining, and social-distancing measures. However, the risk of large-scale epidemics in densely populated environments requires specific consideration in preparedness planning. Prioritization of these settings in vaccination strategies should minimize the risk of future resurgences and potential spillover of transmission to the wider community.

Objectives: This first cross-sectional survey on latent tuberculosis infection (LTBI) in Singapore was performed by utilizing the QuantiFERON Gold In-tube (QFT-GIT) assay to collect data on the prevalence of LTBI and to identify potential risk factors associated with LTBI. Methods: Nationwide household addresses were selected randomly for enumeration, and Singaporeans or Permanent Residents aged 18–79 years were identified. One eligible member per household was selected using the Kish grid. Each participant answered a questionnaire assessing their medical history (including tuberculosis (TB)), socio-economic factors, and lifestyle factors. They also provided a blood specimen for the QFT-GIT assay. Participants with a positive QFT-GIT result were defined as having LTBI if they were asymptomatic. To identify independent risk factors, adjusted hazard ratios were obtained using the multivariable modified Breslow–Cox proportional hazards model. Results: An overall QFT-GIT positivity rate of 12.7% was detected amongst 1682 Singapore residents. There was a wide variation in the positivity rate according to the participants’ country of birth. Higher LTBI prevalence was also significantly associated with increasing age, lower educational and socio-economic status, and alcohol use. Conclusions: Given the high prevalence of LTBI amongst foreign-born residents from regional countries, similar studies should be conducted amongst migrants in Singapore to improve national guidelines on screening and preventive treatment against LTBI. Keywords: Latent tuberculosis, Interferon-gamma release assay, Prevalence, Risk factors, Population