Sze Lok Stefan Ma
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ephmsls@nus.edu.sg
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Publication Effectiveness of Containment Measures Against COVID-19 in Singapore Implications for Other National Containment Efforts(LIPPINCOTT WILLIAMS & WILKINS, 2021-01-01) Pung, Rachael; COOK,ALEXANDER RICHARD; Chiew, Calvin J; Clapham, Hannah E; SUN YINXIAOHE; Li, Zongbin; DICKENS, BORAME SUE LEE; MA SZE LOK STEFAN; Mak, Kenneth; TAN CHORH CHUAN; Heng, Derrick; Chen I-Cheng Mark; VERNON LEE JIAN MING; Dr Borame Sue Lee Dickens; SAW SWEE HOCK SCHOOL OF PUBLIC HEALTH; OFFICE OF THE PRESIDENTBackground: We hypothesize that comprehensive surveillance of COVID-19 in Singapore has facilitated early case detection and prompt contact tracing and, with community-based measures, contained spread. We assessed the effectiveness of containment measures by estimating transmissibility (effective reproduction number,) over the course of the outbreak. Methods: We used a Bayesian data augmentation framework to allocate infectors to infectees with no known infectors and determine serial interval distribution parameters via Markov chain Monte Carlo sampling. We fitted a smoothing spline to the number of secondary cases generated by each infector by respective onset dates to estimate and evaluated increase in mean number of secondary cases per individual for each day's delay in starting isolation or quarantine. Results: As of April 1, 2020, 1000 COVID-19 cases were reported in Singapore. We estimated a mean serial interval of 4.6 days [95% credible interval (CI) = 4.2, 5.1] with a SD of 3.5 days (95% CI = 3.1, 4.0). The posterior mean was below one for most of the time, peaking at 1.1 (95% CI = 1.0, 1.3) on week 9 of 2020 due to a spreading event in one of the clusters. Eight hundred twenty-seven (82.7%) of cases infected less than one person on average. Over an interval of 7 days, the incremental mean number of cases generated per individual for each day's delay in starting isolation or quarantine was 0.03 cases (95% CI = 0.02, 0.05). Conclusions: We estimate that robust surveillance, active case detection, prompt contact tracing, and quarantine of close contacts kept below one.Publication Gender, ethnicity, health behaviour & self-rated health in Singapore(2007) Lim, W.-Y; Ma, S; Heng, D; Bhalla, V; Chew, S.K; SAW SWEE HOCK SCHOOL OF PUBLIC HEALTHBackground. Self-rated health and the factors that influence it have never been described in Singapore before. This paper presents a descriptive study of self-rated health in a nationally representative cross-sectional survey of 6236 persons. Methods. As part of the National Health Surveillance Survey 2001, 6236 subjects aged 18 years and above were interviewed in the homes of participants by trained interviewers. The subjects were asked "In general, how would you rate your health today?", and given 5 possible responses. These were then categorized as "Good" (very good and good) and "Poor" (moderate, bad and very bad) self-rated health. The association of socio-economic and health behaviour risk factors with good self-rated health was studied using univariate and multivariate logistic regression analysis. Results. Univariate analyses suggest that gender, ethnicity, marital status, education, household income, age, self-reported doctor-diagnosed illnesses, alcohol intake, exercise and BMI are all associated with poor self-rated health. In multivariate regression analyses, gender, ethnicity, household income, age, self-reported illness and current smoking and BMI were associated with poor self-rated health. There are gender differences in the association of various factors such as household income, smoking and BMI to self-rated health. Conclusion. Socioeconomic factors and health behaviours are significantly associated with self-rated health, and gender differences are striking. We discuss why these factors may impact self-rated health and why gender differences may have been observed, propose directions for further research and comment on the public policy implications of our findings. © 2007 Lim et al; licensee BioMed Central Ltd.Publication Modelling the control strategies against dengue in Singapore(2008) Burattini, M.N.; Coutinho, F.A.B.; Lopez, L.F.; Massad, E.; Chen, M.; Chow, A.; Goh, K.T.; Ma, S.; CENTRE FOR MOLECULAR EPIDEMIOLOGY; MEDICINEPublication Age-related changes in the cardiometabolic profiles in Singapore resident adult population: Findings from the national health survey 2010(2016) Loh T.P.; Ma S.; Heng D.; Khoo C.M.; MEDICINE; BIOMED INST FOR GLOBAL HEALTH RES & TECH; SAW SWEE HOCK SCHOOL OF PUBLIC HEALTHWe describe the centile trends of the blood pressure, glycemia and lipid profiles as well as renal function of a representative population who participated in the Singapore National Health Survey in 2010. Representative survey population was sampled in two phases, first using geographical/residential dwelling type stratification, followed up ethnicity. 2, 407 survey participants without any self-reported medical or medication history for diabetes mellitus, hypertension and dyslipidemia were included in this analysis. All biochemistry analyses were performed on Roche platforms. After excluding outliers using Tukey's criteria, the results of the remaining participants were subjected to lambda-mu-sigma (LMS) analysis. In men, systolic blood pressure increased linearly with age. By contrast, an upward inflection around late 40s was seen in women. The diastolic blood pressure was highest in men in the late 30s-50s age group, and in women in the late 50s-60s age group. All glycemia-related parameters, i.e. fasting and 2-hour plasma glucose and HbA1c concentrations increased with age, although the rate of increase differed between the tests. Total cholesterol and LDL-cholesterol concentrations increased with age, which became attenuated between the early 30s and late 50s in men, and declined thereafter. In women, total cholesterol and LDLcholesterol concentrations gradually increased with age until late 30s, when there is an upward inflection, plateauing after late 50s. Our findings indicate that diagnostic performance of laboratory tests for diabetes may be age-sensitive. Unfavourable age-related cardiovascular risk profiles suggest that the burden of cardiovascular disease in this population will increase with aging population. © 2016 Loh et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.Publication Impact of analytical and biological variations on classification of diabetes using fasting plasma glucose, oral glucose tolerance test and HbA1c(Nature Publishing Group, 2017) Chai, J.H; Ma, S; Heng, D; Yoong, J; Lim, W.-Y; Toh, S.-A; Loh, T.P; MEDICINE; BIOMED INST FOR GLOBAL HEALTH RES & TECH; SAW SWEE HOCK SCHOOL OF PUBLIC HEALTHHistorically, diabetes is diagnosed by measuring fasting (FPG) and two-hour post oral glucose load (OGTT) plasma concentration and interpreting it against recommended clinical thresholds of the patient. More recently, glycated haemoglobin A1c (HbA1c) has been included as a diagnostic criterion. Within-individual biological variation (CVi), analytical variation (CVa) and analytical bias of a test can impact on the accuracy and reproducibility of the classification of a disease. A test with large biological and analytical variation increases the likelihood of erroneous classification of the underlying disease state of a patient. Through numerical simulations based on the laboratory results generated from a large population health survey, we examined the impact of CVi, CVa and bias on the classification of diabetes using fasting plasma glucose (FPG), oral glucose tolerance test (OGTT) and HbA1c. From the results of the simulations, HbA1c has comparable performance to FPG and is better than OGTT in classifying subjects with diabetes, particularly when laboratory methods with smaller CVa are used. The use of the average of the results of the repeat laboratory tests has the effect of ameliorating the combined (analytical and biological) variation. The averaged result improves the consistency of the disease classification. © 2017 The Author(s).Publication Influenza-associated deaths in tropical Singapore(Centers for Disease Control and Prevention (CDC), 2006) Chow, A; Ma, S; Ai, E.L; Suok, K.C; SAW SWEE HOCK SCHOOL OF PUBLIC HEALTHWe used a regression model to examine the impact of influenza on death rates in tropical Singapore for the period 1996-2003. Influenza A (H3N2) was the predominant circulating influenza virus subtype, with consistently significant and robust effect on mortality rates. Influenza was associated with an annual death rate from all causes, from underlying pneumonia and influenza, and from underlying circulatory and respiratory conditions of 14.8 (95% confidence interval 9.8-19.8), 2.9 (1.0-5.0), and 11.9 (8.3-15.7) per 100,000 person-years, respectively. These results are comparable with observations in the United States and subtropical Hong Kong. An estimated 6.5% of underlying pneumonia and influenza deaths were attributable to influenza. The proportion of influenza-associated deaths was 11.3 times higher in persons age ?65 years than in the general population. Our findings support the need for influenza surveillance and annual influenza vaccination for at-risk populations in tropical countries.Publication Modelling the control strategies against dengue in Singapore(2008-03) Burattini, M.N.; Chen, M.; Chow, A.; Coutinho, F.A.B.; Goh, K.T.; Lopez, L.F.; Ma, S.; Massad, E.; CENTRE FOR MOLECULAR EPIDEMIOLOGY; COMMUNITY,OCCUPATIONAL & FAMILY MEDICINENotified cases of dengue infections in Singapore reached historical highs in 2004 (9459 cases) and 2005 (13 817 cases) and the reason for such an increase is still to be established. We apply a mathematical model for dengue infection that takes into account the seasonal variation in incidence, characteristic of dengue fever, and which mimics the 2004-2005 epidemics in Singapore. We simulated a set of possible control strategies and confirmed the intuitive belief that killing adult mosquitoes is the most effective strategy to control an ongoing epidemic. On the other hand, the control of immature forms was very efficient in preventing the resurgence of dengue epidemics. Since the control of immature forms allows the reduction of adulticide, it seems that the best strategy is to combine both adulticide and larvicide control measures during an outbreak, followed by the maintenance of larvicide methods after the epidemic has subsided. In addition, the model showed that the mixed strategy of adulticide and larvicide methods introduced by the government seems to be very effective in reducing the number of cases in the first weeks after the start of control. © 2007 Cambridge University Press.Publication Societal learning in epidemics: Intervention effectiveness during the 2003 SARS outbreak in Singapore(Public Library of Science, 2006) Drake J.M.; Chew S.K.; Ma S.; SAW SWEE HOCK SCHOOL OF PUBLIC HEALTHBackground. Rapid response to outbreaks of emerging infectious diseases is impeded by uncertain diagnoses and delayed communication. Understanding the effect of inefficient response is a potentially important contribution of epidemic theory. To develop this understanding we studied societal learning during emerging outbreaks wherein patient removal accelerates as information is gathered and disseminated. Methods and Findings. We developed an extension of a standard outbreak model, the simple stochastic epidemic, which accounts for societal learning. We obtained expressions for the expected outbreak size and the distribution of epidemic duration. We found that rapid learning noticeably affects the final outbreak size even when learning exhibits diminishing returns (relaxation). As an example, we estimated the learning rate for the 2003 outbreak of severe acute respiratory syndrome (SARS) in Singapore. Evidence for relaxation during the first eight weeks of the outbreak was inconclusive. We estimated that if societal learning had occurred at half the actual rate, the expected final size of the outbreak would have reached nearly 800 cases, more than three times the observed number of infections. By contrast, the expected outbreak size for societal learning twice as effective was 116 cases. Conclusion. These results show that the rate of societal learning can greatly affect the final size of disease outbreaks, justifying investment in early warning systems and attentiveness to disease outbreak by both government authorities and the public. We submit that the burden of emerging infections, including the risk of a global pandemic, could be efficiently reduced by improving procedures for rapid detection of outbreaks, alerting public health officials, and aggressively educating the public at the start of an outbreak. © 2006 Drake et al.Publication Risk scorecard to minimize impact of COVID-19 when reopening(NLM (Medline), 2021-07-23) Lim, Shin B.; Pung, Rachael; Tan, Kellie; Lang, Jocelyn H. S.; Yong, Dominique Z. X.; Teh, Shi-Hua; Quah, Elizabeth; Sun, Yinxiaohe; Ma, Stefan; Lee, Vernon J. M.; SAW SWEE HOCK SCHOOL OF PUBLIC HEALTHBACKGROUND: We present a novel approach for exiting coronavirus disease 2019 (COVID-19) lockdowns using a 'risk scorecard' to prioritize activities to resume whilst allowing safe reopening. METHODS: We modelled cases generated in the community/week, incorporating parameters for social distancing, contact tracing and imported cases. We set thresholds for cases and analysed the effect of varying parameters. An online tool to facilitate country-specific use including the modification of parameters (https://sshsphdemos.shinyapps.io/covid_riskbudget/) enables visualization of effects of parameter changes and trade-offs. Local outbreak investigation data from Singapore illustrate this. RESULTS: Setting a threshold of 0.9 mean number of secondary cases arising from a case to keep R?1. CONCLUSIONS: Countries can utilize a 'risk scorecard' to balance relaxations for travel and domestic activity depending on factors that reduce disease impact, including hospital/ICU capacity, contact tracing, quarantine and vaccination. The tool enabled visualization of the combinations of imported cases and activity levels on the case numbers and the trade-offs required. For vaccination, a reduction factor should be applied both for likelihood of an infected case being present and a close contact getting infected. © International Society of Travel Medicine 2021. Published by Oxford University Press.Publication Influenza-associated hospitalizations, Singapore, 2004-2008 and 2010-2012(Centers for Disease Control and Prevention (CDC), 2014) Ang, L.W; Lim, C; Jian Ming Lee, V; Ma, S; Tiong, W.W; Ooi, P.L; Tzer Pin Lin, R; James, L; Cutter, J; SAW SWEE HOCK SCHOOL OF PUBLIC HEALTH; PATHOLOGYStudies of influenza-associated hospitalizations in tropical settings are lacking. To increase understanding of the effect of influenza in Singapore, we estimated the agespecific influenza-associated hospitalizations for pneumonia and influenza during 2004-2008 and 2010-2012. The rate of hospitalization was 28.3/100,000 person-years during 2004-2008 and 29.6/100,000 person-years during 2010-2012. The age-specific influenza-associated hospitalization rates followed a J-shaped pattern: rates in persons >75 years of age and in children <6 months of age were >47 times and >26 times higher, respectively, than those for persons 25-44 years of age. Across all ages during these 2 study periods, ?12% of the hospitalizations for pneumonia and influenza were attributable to influenza. The rates and proportions of hospitalizations attributable to influenza, particularly among the very young and the elderly, are considerable in Singapore and highlight the importance of vaccination in protecting populations at risk. © 2014, Emerging Infectious Diseases. All rights reserved.