Evaluation of the Effectiveness of Surveillance and Containment Measures for the First 100 Patients with COVID-19 in Singapore - January 2-February 29, 2020.

Coronavirus disease 2019 (COVID-19) was first reported in Wuhan, China, in December 2019, and has since spread globally, resulting in >95,000 confirmed COVID-19 cases worldwide by March 5, 2020 (1). Singapore adopted a multipronged surveillance strategy that included applying the case definition at medical consults, tracing contacts of patients with laboratory-confirmed COVID-19, enhancing surveillance among different patient groups (all patients with pneumonia, hospitalized patients in intensive care units [ICUs] with possible infectious diseases, primary care patients with influenza-like illness, and deaths from possible infectious etiologies), and allowing clinician discretion (i.e., option to order a test based on clinical suspicion, even if the case definition was not met) to identify COVID-19 patients. Containment measures, including patient isolation and quarantine, active monitoring of contacts, border controls, and community education and precautions, were performed to minimize disease spread. As of March 5, 2020, a total of 117 COVID-19 cases had been identified in Singapore. This report analyzes the first 100 COVID-19 patients in Singapore to determine the effectiveness of the surveillance and containment measures. COVID-19 patients were classified by the primary means by which they were detected. Application of the case definition and contact tracing identified 73 patients, 16 were detected by enhanced surveillance, and 11 were identified by laboratory testing based on providers' clinical discretion. Effectiveness of these measures was assessed by calculating the 7-day moving average of the interval from symptom onset to isolation in hospital or quarantine, which indicated significant decreasing trends for both local and imported COVID-19 cases. Rapid identification and isolation of cases, quarantine of close contacts, and active monitoring of other contacts have been effective in suppressing expansion of the outbreak and have implications for other countries experiencing outbreaks.

Differential age-specific distribution of influenza virus types and subtypes in tropical Singapore, 2011 to 2017.

Surveillance and reporting of epidemiological features of seasonal influenza mostly are aggregates across all-ages. We investigated age-specific differences in distribution of influenza virus (sub)types in tropical Singapore, using laboratory-confirmed virological data collected under the national influenza surveillance programme from 2011 to 2017. The proportion of influenza-positive specimens from outpatients with influenza-like illness was used as an indicator of influenza activity in the community. The highest influenza positivity for age groups of 5 to 14 years and 15 to 64 years coincided in the same month in 5 out of the 7 years under study. Influenza positivity was lowest in young children <5 years of age compared with older age groups. Influenza A(H3N2) was most prevalent in the community except in 2012 when a predominance of influenza B was observed. The dominant virus (sub)type varied across the years in children <5 years and 5 to 14 years of age. Influenza A(H3N2) was the predominant circulating virus subtype among elderly persons aged ≥65 years during the 7-year period, and among adults aged 15 to 64 years since 2013. Knowledge about the age-specific differences in distribution of influenza virus (sub)types helps to facilitate better understanding of seasonal epidemics and to inform targeted strategies in prevention and control of influenza virus transmission.

Particulate air pollution on cardiovascular mortality in the tropics: impact on the elderly.

BACKGROUND: Air pollution has a significant health impact. Most data originate from temperate regions. We aim to study the health impact of air pollution, particularly among the elderly, in a tropical region. METHODS: A daily time-series analysis was performed to estimate excess risk (ER) of various air pollutants on daily death counts amongst the general population in Singapore from 2001 to 2013. Air pollutants included particulate matters smaller than 10 µm, and 2.5 µm (PM10, PM2.5), carbon monoxide (CO), nitrogen dioxide (NO2), ozone (O3) and sulphur dioxide (SO2). The studied outcomes were non-accidental and cardiovascular mortality. Single-day lag and distributed lag models were studied and adjusted for confounders. RESULTS: In single-day lag models, a 10 µg/m3 increase in particulate matter was associated with significant increases in non-accidental (PM10 ER: 0.627%; 95% confidence interval (CI): 0.260-0.995% and PM2.5 ER: 0.660%; 95% CI: 0.204-1.118%) and cardiovascular mortality (PM10 ER: 0.897; 95% CI: 0.283-1.516 and PM2.5 ER: 0.883%; 95% CI: 0.121-1.621%). This was significant in the elderly ≥ 65 years but not in those < 65 years and were seen in the acute phase of lag 0-5 days. Effects by other pollutants were minimal. For cardiovascular mortality, the effects turned protective at a cumulative lag of 30 days in the elderly and could due to "harvesting". CONCLUSIONS: These first contemporary population-based data from an equatorial country with tropical climate show that exposure to particulate air pollution was significantly associated with non-accidental mortality and cardiovascular mortality, especially in the elderly.

The 2016 Singapore Zika virus outbreak did not cause a surge in Guillain-Barré syndrome.

Although individuals with Zika virus (ZIKV) antibodies were reported in Malaya in mid-1950s, entomological and human surveillance in Singapore did not identify autochthonous transmission until the outbreak of August-November, 2016. A total of 455 cases from 15 separate clusters were identified. We asked if this ZIKV outbreak increased the incidence of Guillain-Barré syndrome (GBS) and aimed to characterize these cases. Eleven GBS cases, consecutively enrolled into our prospective GBS database from onset to 4 weeks after outbreak, and six controls, comprising three GBS patients enrolled before outbreak and three non-GBS patients, were examined for evidence of recent ZIKV infection. We performed serum, urine ZIKV RT-PCR, ZIKV serology, and virus neutralization assays, accounting for cross-reaction and co-infection with dengue (DENV). We found five GBS cases with only serological evidence of recent ZIKV infection (including one ZIKV-DENV co-infection). A temporal relationship with ZIKV outbreak was unlikely as two cases were GBS controls enrolled 3 months before outbreak. None reported symptoms of ZIKV infection. In addition, compared to last 10 years the national number of GBS hospitalizations did not increase during and immediately after outbreak. We conclude the 2016 Singapore ZIKV outbreak did not cause a change in GBS epidemiology.

Seroprevalence of vaccine-preventable diseases among children and adolescents in Singapore: Results from the National Paediatric Seroprevalence Survey 2018.

OBJECTIVES: The Ministry of Health (MOH), Singapore, conducted the National Paediatric Seroprevalence Survey 2018 (NPSS 2018) to estimate the latest immunity levels against measles, rubella, varicella, diphtheria, tetanus and hepatitis B, and the seroprevalence of chronic hepatitis B virus (HBV) carriage in children and adolescents in Singapore. METHODS: The survey involved prospective collection of residual sera from 1,200 children and adolescents aged 1-17 years in two public acute hospitals. Enzyme-linked immunosorbent assays (EIA) or plague reduction neutralisation tests (PRNT) were used to determine the seroprevalence of the vaccine-preventable diseases. RESULTS: Overall prevalence of measles and rubella antibodies among Singaporean children and adolescents aged 1-17 years were 98.2% (95% CI: 91.2-98.8%) and 94.8% (95% CI: 93.4-95.9%) respectively. 97.1% (95% CI: 96.0-97.9%) of subjects had at least basic protection against diphtheria, while 89.3% (95% CI: 87.5-91.0%) were protected against tetanus. The prevalence of chronic HBV carriage was 0.4% (95% CI: 0.2-1.0%), while 45.7% (95% CI: 42.9-48.5%) were immune against HBV. The seroprevalence for varicella antibodies was 52.9% (95% CI: 50.1-55.7%). Concordance between vaccination status and seroprevalence was observed for measles, rubella, diphtheria and tetanus. CONCLUSION: Singapore's children and adolescents are well-protected against measles, rubella, diphtheria and tetanus. Continual efforts in ensuring high vaccination coverage should be sustained.

Estimates of influenza-associated hospitalisations in tropical Singapore, 2010-2017: Higher burden estimated in more recent years.

BACKGROUND: We previously estimated Singapore's influenza-associated hospitalisation rate for pneumonia and influenza (P&I) in 2010-2012 to be 29.6 per 100 000 person-years, which corresponds to 11.2% of all P&I hospitalisations. OBJECTIVES: This study aims to update Singapore's estimates of the influenza-associated pneumonia and influenza (P&I) hospitalisation burden using the latest data from 2010 to 2017. METHODS: We estimated the number of P&I hospitalisations associated with influenza using generalised additive models. We specified the weekly number of admissions for P&I and the weekly influenza positivity in the models, along with potential confounders such as weekly respiratory syncytial virus (RSV) positivity and meteorological data. RESULTS: In 2010-2017, 16.3% of all P&I hospitalisations in Singapore were estimated to be attributed to influenza, corresponding to an excess influenza-associated P&I hospitalisation rate of 50.1 per 100 000 person-years. Higher excess rates were estimated for children aged 0-4 years (186.8 per 100 000 person-years) and elderly aged ≥ 65 years (338.0 per 100 000 person-years). Higher influenza-associated hospitalisation rates were estimated for 2016 and 2017 (67.9 and 75.1 per 100 000 persons, respectively) years when the influenza A(H3N2) subtype was dominant. CONCLUSION: Influenza burden in Singapore has increased since 2010. Influenza vaccination programmes should continue to be prioritised for the young and the elderly.

A 15-year review of dengue hospitalizations in Singapore: Reducing admissions without adverse consequences, 2003 to 2017.

OBJECTIVES: Since the 1990s, Singapore has experienced periodic dengue epidemics of increasing frequency and magnitude. In the aftermath of the 2004-2005 dengue epidemic, hospitals refined their admission criteria for dengue cases to right-site dengue case management and reduce the burden of healthcare utilization and negative outcomes. In this study, we describe the national trends of hospital admissions for dengue and disease severity in terms of length of stay (LOS), admission to the intensive care unit (ICU) and death in hospital, and case fatality rate (CFR) in Singapore. METHODS: We conducted a retrospective study of notified cases and laboratory confirmed dengue patients admitted to all public and private hospitals between 2003 and 2017. Case notifications for dengue and hospitalization records were extracted from national databases. RESULTS: The proportion of dengue cases hospitalized was lower in recent years; 28.9% in the 2013-2014 epidemic, compared to 93.2% in the 2004-2005 epidemic, and 58.1% in the 2007 epidemic. Median LOS remained stable over the years; overall LOS was 3 to 4 days and ICU stay was 2 to 3 days. Less than 2% of hospitalized patients were admitted to the ICU. Overall CFR was low and remained below 0.5%. The proportions of dengue cases hospitalized and patients admitted to the ICU were highest in the elderly aged 65 years and older. CONCLUSIONS: While the proportion of dengue cases hospitalized saw a drastic decline due to more selective admission criteria, there was no concomitant increase in adverse outcomes, suggesting that admission criteria were appropriate to focus on severe dengue cases. Further studies are needed to optimize dengue management in older adults who are more likely to be hospitalized with greater disease severity, given the higher proportions of hospitalizations and severe disease among older adults.

Evaluating the effectiveness of the influenza vaccine during respiratory outbreaks in Singapore's long term care facilities, 2017.

Influenza outbreaks occur periodically in Long Term Care Facilities (LTCFs) and vaccination is critical in preventing influenza infections. We evaluated the influenza vaccine effectiveness (VE) during respiratory outbreaks in LTCFs reported to the Ministry of Health, Singapore in 2017. A test-negative design was used to estimate the ratio of the odds of testing positive for influenza among vaccinated individuals to the odds among unvaccinated individuals. The VE was calculated as (1-odds ratio) × 100%. For adjusted VE, the estimates were derived using logistic regression adjusted for age group, gender, month of illness, and number of days from date of illness onset till to swab collection date. Estimates by influenza subtypes and post-vaccination time periods (15-180 days & 181-365 days) were also calculated using stratified data. 264 individuals, with 118 laboratory-confirmed influenza cases [32 A(H1N1)pdm09, 75 A(H3N2), 11 A(untypable)], were included in the analysis. No one was identified to be infected with influenza B. The overall adjusted VE estimate was 40.5% (95% CI: -12.2-68.5%), while the subtype-specific adjusted VE estimates were -43.4% (95% CI: -312.4-50.2%) against A(H1N1)pdm09 and 57.1% (95% CI: 5.7-80.5%) against A(H3N2). At 15-180 days post-vaccination period, the adjusted VEs were 59.3% (95% CI: 18.0-79.8%) against all influenza, 35.4% (95% CI: -123.5-81.3%) against A(H1N1)pdm09 and 67.9% (95% CI: 22.5-86.7%) against A(H3N2). Estimates were not significant at 181-365 days post-vaccination. The influenza vaccine showed varying effectiveness among individuals in Singapore's LTCFs in 2017, with a higher effectiveness among those who were more recently vaccinated. It remains an important tool in preventing influenza infections, especially for those who are at high risk of influenza-related complications.