Force of Infection and True Infection Rate of Dengue in Singapore: Implications for Dengue Control and Management.

National data on dengue notifications do not capture all dengue infections and do not reflect the true intensity of disease transmission. To assess the true dengue infection rate and disease control efforts in Singapore, we conducted age-stratified serosurveys among residents after a 2013 outbreak that was the largest dengue outbreak on record. The age-weighted prevalence of dengue immunoglobulin G among residents was 49.8% (95% confidence interval: 48.4, 51.1) in 2013 and 48.6% (95% confidence interval: 47.0, 50.0) in 2017; prevalence increased with age. Combining these data with those from previous serosurveys, the year-on-year estimates of the dengue force of infection from 1930 to 2017 revealed a significant decrease from the late 1960s to the mid-1990s, after which the force of infection remained stable at approximately 10 per 1,000 persons per year. The reproduction number (R0) had also declined since the 1960s. The reduction in dengue transmission may be attributed to the sustained national vector program and partly to a change in the age structure of the population. The improved estimated ratio of notified cases to true infections, from 1:14 in 2005-2009 to 1:6 in 2014-2017, signifies that the national notification system, which relies on diagnosed cases, has improved over time. The data also suggest that the magnitudes of dengue epidemics cannot be fairly compared across calendar years and that the current disease control program remains applicable.

Prevalence of hepatitis C virus infection and the IL28B genotype polymorphism among blood donors and high-risk populations.

INTRODUCTION: To study the prevalence of hepatitis C virus (HCV) infection in blood donor (BD), haemodialysis (HD) and intravenous drug user (IVDU) populations in Singapore and assess the IL28B polymorphism if HCV positive. METHODS: The BD population were healthy volunteers, the HD population were patients who were on haemodialysis for at least six months of follow-up between January 2009 and December 2014. IVDU population was from inmates at halfway houses who consented. RESULTS: Between 2011 and 2014, of 161,658 individuals who underwent screening prior to blood donation, 95 (0.059%) were positive for HCV. Of the 42 sera available, common genotypes (GTs) were GT-3 (47.6%) and GT-1 (31.0%). Of 1,575 HD patients, 2.2% were anti-HCV positive. The HCV GT distribution was HCV GT-1 (32.4%), HCV GT-3 (20.5%) and GT-6 (8.8%). 83 halfway house inmates were screened. Of the 47 IVDUs, 36.2% were anti-HCV positive with predominant GT-3 (%). IL28B polymorphism was noted to be CC predominantly 85.3%. CONCLUSION: Prevalence of HCV infection has decreased in both the BD and HD populations. However, it remains high in the IVDU population. GT-1 remains the most common in the HD population; however, GT-3 infection is now more common among the BD population in Singapore. IL28B - CC is the predominant variant among the HCV-infected individuals in Singapore.

Addressing gaps in international blood availability and transfusion safety in low- and middle-income countries: a NHLBI workshop.

In April 2017, a workshop sponsored by the National Heart, Lung, and Blood Institute, Division of Blood Diseases and Resources, and the Center for Translation Research and Implementation Science was held to discuss blood availability and transfusion safety in low- and middle-income countries (LMICs). The purpose of the workshop was to identify research opportunities for implementation science (IS) to improve the availability of safe blood and blood components and transfusion practices in LMICs. IS describes the late stages of the translational research spectrum and studies optimal and sustainable strategies to deliver proven-effective interventions. Regional working groups were formed to focus on opportunities and challenges in East Africa, Central/West Africa, Middle East and North Africa, Latin America and the Caribbean, Southeast Asia, Western Pacific Asia, Eastern Europe, and Central Asia. The need for an "adequate supply of safe blood" emerged as the major overriding theme. Among the regional working groups, common cross-cutting themes were evident. The majority of research questions, priorities, and strategies fell into the categories of blood availability, blood transfusion safety, appropriate use of blood, quality systems, health economics and budgeting, and training and education in IS. The workshop also brought into focus inadequate country-level data that can be used as the basis for IS initiatives. A mixed approach of needs assessment and targeted interventions with sufficient evidence base to move toward sustainment is an appropriate next step for blood availability and transfusion safety research in LMICs.

Dengue seroprevalence of healthy adults in Singapore: serosurvey among blood donors, 2009.

Routine national notifications of dengue cases typically do not reflect the true dengue situation due to large proportion of unreported cases. Serosurveys, when conducted periodically, could shed light on the true dengue infections in the population. To determine the magnitude of dengue infections of the adult population in Singapore following the outbreak in 2007, we performed a cross-sectional study on blood donor samples from December 2009 to February 2010. The residual blood of 3,995 donors (aged 16-60 years) was screened for the presence of dengue-specific immunoglobulin G (IgG) and IgM using enzyme-linked immunosorbent assay (ELISA) kits. The age-weighted IgG prevalence of residents was 50.8% (N = 3,627, 95% confidence interval [CI] = 49.4-52.3%). Dengue IgG prevalence increased with age, with the lowest in 16-20 years age group (16.1%) and the highest in 56-60 years age group (86.6%). Plaque reduction neutralization test (PRNT) on samples of young resident adults (aged 16-30 years) revealed lower prevalence of neutralizing antibodies to each serotype, ranging from 5.4% to 20.3% compared with the older age groups. The level of exposure to dengue among the young adults is relatively low despite the endemicity of the disease in Singapore. It partially explains the population's susceptibility to explosive outbreaks and the high incidence rate among young adults.

Occult hepatitis B infection in blood donors from South East Asia: molecular characterisation and potential mechanisms of occurrence.

OBJECTIVE: To investigate the molecular basis of occult hepatitis B virus (HBV) infection (OBI) in Asian blood donors. DESIGN: OBI donors from Hong Kong, Malaysia, Singapore, Taiwan and Thailand were tested for HBV serological markers, and strains were molecularly characterised. RESULTS: Among 138 confirmed OBI carriers (median age 47 years), HBV genotypes B and C were dominant (60% and 34%, respectively) in agreement with the genotype distribution in chronically infected donors in the region. Viral load ranged between unquantifiable and 3670 IU/ml (median 11 IU/ml). Eleven per cent of OBIs showed an unusual anti-HBs-only serological profile without evidence of past vaccination for most of these individuals. Occult HBV strains showed a higher genetic diversity than strains from matched hepatitis B surface antigen (HBsAg)+ donors, irrespective of genotype. No unique genetic signature or evidence of reduced replication competence was found. Mutations in the vicinity of the pre-S2/S splice donor site were common in OBI(B) (44%) and OBI(C) (36%) strains. S regions from four OBI cases were transfected in HuH7 cells. Results showed limited HBsAg secretion and suggested that mutations disrupting the splice donor site structure may affect pre-S2/S mRNA splicing. CONCLUSIONS: There is indirect evidence that incomplete immune control is involved in the occurrence of OBI in Asian blood donors infected with genotypes B and C as observed in Europe with genotype A2 but to a lower extent than with genotype D. A post-transcriptional mechanism may play a role in HBsAg expression in some OBIs irrespective of HBV genotype.

When less is more: can we abandon prophylactic platelet transfusion in Dengue fever?

Dengue fever (DF) has several hematological manifestations including thrombocytopenia and increased bleeding risk. Prophylactic platelet transfusion-in the absence of major bleeding-is utilized in DF with thrombocytopenia with the intention of preventing hemorrhagic complications. However, prophylactic platelet transfusion in DF is neither standardized nor supported by clinical evidence. We conclude that risks, costs and poor resource utilization associated with prophylactic platelet transfusion in DF far outweigh any potential hematological benefit, and as such, should not constitute routine clinical practice.

Role of regulatory agencies.

In this paper the authors discuss the role of regulation in assuring blood safety. After an overview of the subject by a leading expert, examples are provided of regulatory systems for blood transfusion services in several countries and regions. Additionally, the perspective of WHO is given on the essential role of national regulatory authorities in assuring the quality of national blood programmes. Collectively, the sections of this paper afford an opportunity for readers to make comparisons among different regulatory frameworks and to "benchmark" among the existing systems. Despite many differences in approach, a clear pattern emerges of worldwide efforts to strengthen blood regulatory systems.