Singapore's 5 decades of dengue prevention and control-Implications for global dengue control

Global dengue fever management in health systems: identifying strategies, challenges and solutions - a scoping review protocol

INTRODUCTION

Dengue fever, the fastest-spreading mosquito-borne viral disease, poses a significant global public health challenge. Over the past two decades, its rapid spread has been driven by urbanisation, climate change and international travel, particularly affecting tropical and subtropical regions. Despite its considerable economic burden, effective antiviral treatments and vaccines remain unavailable. This study aims to bridge gaps in dengue fever management by systematically identifying and analysing strategies, challenges and solutions adopted within health systems worldwide.

METHODS AND ANALYSIS

This scoping review will adopt the methodological framework of Arksey and O'Malley. A comprehensive search will be conducted across databases including PubMed, Scopus, Web of Science, Embase and Cochrane Library, along with grey literature sources and manual reference list searches, covering the period from 2003 to 2024, limited to English-language publications. Search strategies will be developed using controlled vocabulary and key terms associated with various components of dengue fever management. Two independent reviewers will screen titles and abstracts based on predefined inclusion and exclusion criteria, followed by full text screening to determine final eligibility. A descriptive numerical analysis will summarise the characteristics of included studies, while a thematic analysis will provide an overview of the literature, encompassing strategies, challenges and solutions.

ETHICS AND DISSEMINATION

This study, approved by the Medical Ethics Committee of Mashhad University of Medical Sciences (IR.MUMS.REC.1403.142), adheres to ethical guidelines for handling publicly available data. All findings will be transparently reported and disseminated through peer-reviewed journals, relevant conferences and stakeholder engagement.

Adjacent spillover efficacy of Wolbachia for control of dengue: emulation of a cluster randomised target trial

BACKGROUND

Matings between male Aedes aegypti mosquitoes infected with wAlbB strain of Wolbachia and wild-type females yield non-viable eggs, thereby suppressing Ae. aegypti abundance in the field. We evaluated the spillover efficacy of releasing wAlbB-infected Ae. aegypti male mosquitoes to suppress dengue in sites adjacent to release sites (spillover sites).

METHODS

The protocol of a two-arm cluster-randomised test-negative controlled trial (cRCT) was specified and emulated using a nationally representative dengue test-negative/positive database of 454,437 individuals reporting for febrile illness to primary or secondary care in public healthcare institutions. Spillover intervention sites were defined by geolocating locations which were adjacent to, i.e. shared geographical borders with, actual Wolbachia intervention sites. We built a cohort of individuals who resided in spillover sites versus a comparator control group who resided in sites which did not receive Wolbachia interventions. We emulated a constrained randomisation protocol used in cRCTs to balance dengue risk between spillover and control arms in the pre-intervention period. We matched individuals reporting for testing in intervention and control groups by calendar time and a high-dimensional battery of sociodemographic, environmental and anthropogenic variables. Intention-to-treat analysis was conducted to estimate the protective efficacy against dengue given spillover Wolbachia exposure.

RESULTS

The final cohort consisted of 2354 matched individuals residing in Wolbachia spillover and control sites for at least 3 months in the study period. Compared to the controls, individuals residing in spillover sites for 3 or more months were associated with a 45% (OR: 0.55, 95% CI: 0.42‒0.74) reduction in risk of contracting dengue. Higher durations of spillover Wolbachia exposure also modestly increased protective efficacies. Compared to the control arm, the proportion of virologically confirmed dengue cases was lower in the spillover arm overall and across each subgroup. Protective efficacies were found across all years, age and sex subgroups.

CONCLUSIONS

Our results demonstrated the potential of Wolbachia-mediated sterility for reducing the risk of contracting dengue even in sites which were not directly treated by the intervention.

Exploiting Wolbachia as a Tool for Mosquito-Borne Disease Control: Pursuing Efficacy, Safety, and Sustainability

Despite the application of control measures, mosquito-borne diseases continue to pose a serious threat to human health. In this context, exploiting Wolbachia, a common symbiotic bacterium in insects, may offer effective solutions to suppress vectors or reduce their competence in transmitting several arboviruses. Many Wolbachia strains can induce conditional egg sterility, known as cytoplasmic incompatibility (CI), when infected males mate with females that do not harbor the same Wolbachia infection. Infected males can be mass-reared and then released to compete with wild males, reducing the likelihood of wild females encountering a fertile mate. Furthermore, certain Wolbachia strains can reduce the competence of mosquitoes to transmit several RNA viruses. Through CI, Wolbachia-infected individuals can spread within the population, leading to an increased frequency of mosquitoes with a reduced ability to transmit pathogens. Using artificial methods, Wolbachia can be horizontally transferred between species, allowing the establishment of various laboratory lines of mosquito vector species that, without any additional treatment, can produce sterilizing males or females with reduced vector competence, which can be used subsequently to replace wild populations. This manuscript reviews the current knowledge in this field, describing the different approaches and evaluating their efficacy, safety, and sustainability. Successes, challenges, and future perspectives are discussed in the context of the current spread of several arboviral diseases, the rise of insecticide resistance in mosquito populations, and the impact of climate change. In this context, we explore the necessity of coordinating efforts among all stakeholders to maximize disease control. We discuss how the involvement of diverse expertise-ranging from new biotechnologies to mechanistic modeling of eco-epidemiological interactions between hosts, vectors, Wolbachia, and pathogens-becomes increasingly crucial. This coordination is especially important in light of the added complexity introduced by Wolbachia and the ongoing challenges posed by global change.

Evaluating the effectiveness of dengue surveillance in the tropical and sub-tropical Asian nations through dengue case data from travelers returning to the five Western Pacific countries and territories

INTRODUCTION

Dengue, affecting over 3.9 billion people, is a significant health threat globally. Despite a tenfold increase in reported cases from 2000 to 2020, underreporting remains an issue. Our study utilized traveler data from the five Western Pacific countries and territories as sentinel sites, to examine dengue surveillance in Southeast and South Asia.

METHODS

We reported dengue cases among returning travelers (2010-2018) and computed dengue incidence per 100,000 travelers for each destination country. We compared officially reported dengue incidence per 100,000 inhabitants of the destination country with estimated incidence per 100,000 travelers, using Pearson's correlation coefficient.

RESULTS

Key findings revealed eight Southeast and South Asia countries as popular destinations for our sentinel sites, with Australia exhibiting the highest incidence (40.7 per 100,000 travelers). Dengue incidence variations were evident, with Malaysia showing a sharp increase over time. Correlation analysis showed strong links in Malaysia (r = 0.66-0.92) and weaker connections in India (r = -0.54-0.76) between dengue incidence among inhabitants and travelers.

CONCLUSION

Systematically collected dengue surveillance data from returning travelers can serve as a proxy for dengue incidence in the destination country and can be used to assess the robustness of the country's dengue surveillance.

Suppression of Aedes aegypti may not affect sympatric Aedes albopictus populations: findings from two years of entomological surveillance in Singapore

Globally, multiple trials have successfully demonstrated the effectiveness of novel tools, such as the sterile and incompatible insect techniques, in suppressing Aedes aegypti populations. However, there is concern that Aedes albopictus, another arbovirus-competent vector, may occupy the niches vacated by Ae. aegypti in areas where these species occur in sympatry. Here we investigate these concerns within the context of a Wolbachia-based Ae. aegypti suppression programme in highly urban Singapore, where general mosquito management is sustained through environmental management. Using nationally representative and longitudinal Aedes surveillance data, we show (1) no consistent association of increase in Ae. albopictus abundance with Ae. aegypti population suppression within Wolbachia-Aedes release sites, and (2) no significant change in the vertical spatial distribution of Ae. albopictus in high-rise residential apartment blocks even after two years of Ae. aegypti suppression. Finally, we report that dengue viruses were less prevalent in field Ae. albopictus than in Ae. aegypti, which is consistent with previous findings that Ae. albopictus is a lesser vector than Ae. aegypti in Singapore. Together, these results indicate that suppression of Ae. aegypti in the community may not be directly associated with any increase of Ae. albopictus population or capacity. Nonetheless, the risk of increase in Ae. albopictus population is anticipated if the reduction in disease transmission leads to less aggressive source reduction efforts and environmental management for mosquito control.

COMPARING DETECTIONS OF AEDES AEGYPTI FEMALES USING THREE TYPES OF AUTOCIDAL GRAVID TRAPS

We compared the number of Aedes aegypti females per trap and the number of detections of this mosquito species per week during 8 wk in 3 types of autocidal gravid traps, the Centers for Disease Control and Prevention (CDC) Autocidal Gravid Ovitrap (AGO), Biogents Gravid Aedes Trap (GAT), and Singapore Gravitrap (SGT), in central Puerto Rico. These traps use the same principles for attracting gravid Ae. aegypti females as traditional ovitraps, such as dark colors, standing water, and decomposing plant materials. The traps differ in size, AGO being the biggest and SGT the smallest. Average captures of female Ae. aegypti per trap per week were 11.1, 7.2, and 1.7 in AGO, GAT, and SGT traps, respectively, a pattern consistent with the sizes of the traps. These results indicated that GAT traps and SGT traps captured 35.5% and 84.7% fewer females of Ae. aegypti, respectively, than AGO traps. Although Ae. aegypti was present in all 20 sites during the 8 wk of observations, AGO, GAT, and SGT traps did not catch specimens in 1, 9, and 58 out of 160 observations per trap type (trap-wk), respectively. Trap failures were 1, 6, and 1 for the AGO, GAT, and SGT traps, respectively. Despite the absence of females of Ae. aegypti at some sites and weeks in each of the traps, all 3 traps were able to detect the presence of this mosquito at each of the 20 sites during the 8 wk of observations and could be used for Ae. aegypti surveillance.

Assessing the direct and spillover protective effectiveness of Wolbachia-mediated introgression to combat dengue

BACKGROUND

Dengue remains a global health challenge with limited treatment options, highlighting the need for effective vector control strategies. The introduction of Wolbachia pipientis into Aedes aegypti populations has shown success in reducing dengue transmission across global field trials. However, the spillover effectiveness of the technology on untreated areas is not well-known. This study estimates the spillover protective effectiveness (PE) of Wolbachia-mediated introgression on dengue.

METHODS

We used the synthetic control method (SCM) under assumption of partial interference to evaluate the direct and spillover PEs of Wolbachia-mediated introgression in a long-running operational trial of the intervention in Malaysia. Synthetic controls (SCs), which comprise of a weighted sum of non-spillover controls, were constructed for each directly-treated and spillover site in the pre-intervention period to account for historical imbalances in dengue risk and risk trajectories. SCs were compared to directly/spillover-treated sites to estimate the impact of Wolbachia-introgression on dengue incidence across each site, calendar year and intervention time. Robustness checks, including visual inspections, root-mean-square error (RMSE) calculations, in-space and in-time placebo checks, and permutation tests, were used to inspect the model's ability in attributing dengue incidence reductions to the Wolbachia interventions.

FINDINGS

The direct and spillover PEs of Wolbachia on dengue incidence were expressed as a percentage reduction of dengue incidence, or the absolute case reductions, by comparing SCs to actual intervention/spillover sites. Findings indicate a direct reduction in dengue incidence by 64.35% (95% CI: 63.50-66.71, p < 0.05 using permutation tests) in directly treated areas, corresponding to 1802 (95% CI: 1768-1932) cases averted. Meanwhile, spillover effects contributed to a 37.69% (95% CI: 36.45-38.49, p < 0.05) reduction in adjacent non-intervention areas, accounting for 115 (95% CI: 104-132) absolute cases averted. Tracking PEs by intervention time revealed a dose-response relationship, where PEs increased concomitantly with Wolbachia frequency. Model checks confirmed the robustness of these results, and ascertained that these PEs were not an artefact of poor control selection, pre-trends in dengue incidence or poor predictive ability of the fitted SCs.

INTERPRETATION

Wolbachia-introgression effectively diminished dengue incidence in directly-treated and surrounding spillover regions. This dual effectiveness highlights the potential of Wolbachia-infected mosquitoes as a sustainable, cost-effective strategy against dengue.

FUNDING

This research is hosted by CNRS@CREATE and supported by the National Research Foundation, Prime Minister's Office, Singapore, under its Campus for Research Excellence and Technological Enterprise (CREATE) program, and is funded by the Lee Kong Chian School of Medicine-Ministry of Education Start-Up Grant. The original Hoffmann et al. (2024) study was funded by the Wellcome Trust Awards 226166, 108508, 202888 and the Ministry of Health Malaysia NMRR-16-297-28898.

One Health prevention and preparedness to vector-borne diseases: how should we deal with a multisectoral, multilevel and multigroup governance?

INTRODUCTION

Multifactorial determinants of vector presence, distribution and ability of transmitting diseases, demand holistic approaches that consider eco-biosocial factors, such as One Health (OH), and engage institutions and communities to reduce vulnerability to vector-borne diseases (VBDs). Although the importance of multisectoral, multilevel and multigroup collaboration for prevention and preparedness to VBDs has been promoted by international guidance, evidence about practical experiences adopting a OH approach needs to be gathered and enabling factors for a successful governance highlighted.

METHODS

This study included a rapid literature review coupled with a stakeholder consultation process.

RESULTS

The peer-reviewed literature search identified 1674 articles and 13 articles were finally included in the review. The collaboration and coordination of different sectors and stakeholders allowed to focus resources, and share knowledge and perspectives. To support coordination and collaboration among the stakeholders synergistic interaction mechanisms were created, such as working groups and committees, and connection agents emerged as the main link between institution and communities. These synergies allowed to target the multidimensional drivers of VBDs, supported transversal capacity building and an holistic monitoring evaluation framework, and improved effectiveness and sustainability of the interventions.

CONCLUSION

A OH model highlighting enabling factors for multisectoral, multilevel and multigroup interventions for VBDs prevention and preparedness was developed to support decision-makers and key stakeholders to deal with a OH governance.

Psychological barriers in children: an exploratory study on Dengue transmission using an adapted DIPB scale

Dengue is an arboviral infection found in tropical and subtropical regions transmitted by hematophagous mosquitoes from the genus Aedes spp. and responsible for millions of cases every year. Public campaigns and educational curriculum are designed to educate people, including children. However, what has been reported is that many decide not to follow these guidelines, even though they allegedly know what has to be done. To understand this phenomenon, this study aims to identify psychological barriers behind the adoption of pro-environmental behaviors that seek to reduce Aedes aegypti's population. For that, middle school students participated on two studies responsible for (1) adapting the Dragons of Inaction Psychological Barrier (DIPB) scale to the target group (n = 150) and then (2) testing it on a larger group (n = 449). In the exploratory factor analysis, Bartlett correlation (p < 0.001), Cronbach's alpha (0.83), and KMO analysis (overall MSA = 0.84) showed that data was suited for factor analysis. Five factors were retained by Kaiser Criterion and scree test (i.e., Conflicting goals and unnecessary changes-α 0.76, Interpersonal relations-α 0.72, Conflicting goals and lacking knowledge-α 0.58, Tokenism-α 0.73, and Tokenism toward the government-α 0.66). After that, the scale was tested across 11 different schools, where students also answered a questionnaire about the mosquito. Results suggested that the factors Conflicting goals and lacking knowledge and Tokenism toward the government presented a higher level of agreement for all students (means: 2.6 and 2.12 out of five, respectively). Those who scored higher in the mosquito's questionnaire had factors Conflicting goals and unnecessary change and Interpersonal relations inhibited when compared to others (p < 0.05). These results suggests that future educational campaigns should build different actions that focuses on addressing both internal and external factors, creating a mosaic of projects, with different goals, each aiming different environmental challenges.

Assessing Wolbachia-mediated sterility for dengue control: emulation of a cluster-randomized target trial in Singapore

BACKGROUND

Matings between male Aedes aegypti mosquitoes infected with wAlbB strain of Wolbachia and wildtype females yield non-viable eggs. We evaluated the efficacy of releasing wAlbB-infected Ae. aegypti male mosquitoes to suppress dengue.

METHODS

We specified the protocol of a two-arm cluster-randomized test-negative controlled trial (cRCT) and emulated it using a nationally representative test-negative/positive database of individuals reporting for febrile illness to any public hospital, general practitioner or polyclinic. We retrospectively built a cohort of individuals who reside in Wolbachia locations vs a comparator control group who do not reside in Wolbachia locations, using a nationally representative database of all individuals whom report for febrile illness and were tested for dengue at the Environmental Health Institute/hospital laboratories/commercial diagnostic laboratories, through general practitioner clinic, polyclinic or public/private hospital from epidemiological week (EW) 1 2019 to EW26 2022. We emulated a constrained randomization protocol used in cRCTs to balance dengue risk between intervention and control arms in the pre-intervention period. We used the inverse probability weighting approach to further balance the intervention and control groups using a battery of algorithmically selected sociodemographic, environmental and anthropogenic variables. Intention-to-treat analyses were conducted to estimate the risk reduction of dengue given Wolbachia exposure.

RESULTS

Intention-to-treat analyses revealed that, compared with controls, Wolbachia releases for 3, 6 and ≥12 months was associated to 47% (95% confidence interval: 25-69%), 44% (33-77%) and 61% (38-78%) protective efficacy against dengue, respectively. When exposed to ≥12 months of Wolbachia releases, protective efficacies ranged from 49% (13-72%) to 77% (60-94%) across years. The proportion of virologically confirmed dengue cases was lower overall in the intervention arm. Protective efficacies were found across all years, age and sex subgroups, with higher durations of Wolbachia exposure associated to greater risk reductions of dengue.

CONCLUSION

Results demonstrated that Wolbachia-mediated sterility can strengthen dengue control in tropical cities, where dengue burden is the greatest.

Effectiveness of Wolbachia-mediated sterility coupled with sterile insect technique to suppress adult Aedes aegypti populations in Singapore: a synthetic control study

BACKGROUND

Incompatible insect technique (IIT) coupled with sterile insect technique (SIT) via the release of sterile male Wolbachia-infected mosquitoes is a promising tool for Aedes-borne disease control. Yet, real-world evidence on the suppressive effectiveness of IIT-SIT on mosquito abundance remains mostly limited to small semi-rural village and suburban localities over short trial durations. However, a large proportion of Aedes-borne diseases occur in dense, urban, and high-rise locations, limiting the applicability of previous studies for these settings with high disease burden. The sustainability and use of this technology over multiple years is also unknown.

METHODS

In this synthetic control study, we conducted a large-scale, field trial of IIT-SIT targeting Aedes aegypti among high-rise public housing estates in Singapore, an equatorial city state. Routinely collected data from a large, nationwide surveillance system of 57 990 unique mosquito traps, combined with a high-dimensional set of anthropogenic and environmental confounders were collected to ascertain mosquito abundance and its key drivers. Four townships were selected as the intervention groups (approximate population size of 607 872 residents as of 2022), wherein interventions that combined ITT with SIT over the course of the study period were conducted. Townships were subject to releases of wAlbB-SG male A aegypti mosquitoes twice a week. Data were assessed over the course of epidemiological weeks (EWs), which provide the finest temporal resolution of recorded Wolbachia release schedule and mosquito abundance data. A novel synthetic control framework was then developed to account for the non-randomised and staggered adoption setting of the intervention across trial sectors to identify the direct suppressive effectiveness of IIT-SIT on female A aegypti populations, the spillover effects in non-release areas, and the effect of the intervention on other mosquito populations such as Aedes albopictus. Furthermore, we recalculated effectiveness in terms of calendar time, time since intervention, and over multiple sites to examine heterogeneities in IIT-SIT effectiveness.

FINDINGS

Between EW27 2018 and EW26 2022, Wolbachia releases were conducted across 117 sectors, of which 97 had sufficient trap data, which were collected between EW8 2019 and EW26 2022. We found that Wolbachia-based IIT-SIT reduced wild-type female A aegypti populations by a mean of 62·01% (95% CI 60·68 to 63·26) by 3 months, 78·40% (77·56 to 79·18) by 6 months, and 91·32% (90·95 to 91·66) by at least 18 months of releases. We also found a smaller but non-negligible spillover suppression effect that gradually increased over time (mean spillover intervention effectiveness 61·02% [95% CI 57·89 to 63·72] in adjacent, non-intervention sectors). Although no consistent change in A albopictus populations was seen across the four intervention townships after Wolbachia releases, the average intervention effectiveness on the A albopictus population across all release sectors was -25·80% (95% CI -30·93 to -21·05), which was driven by increases in two towns.

INTERPRETATION

Our results demonstrate the potential of IIT-SIT for strengthening long-term, large-scale vector control in tropical cities, where dengue burden is the greatest. The effect of these interventions in different geographical settings should be assessed in future work.

FUNDING

Singapore's Ministry of Finance, Ministry of Sustainability and the Environment, National Environment Agency, and National Robotics Program.

Discrepancies in dengue burden estimates: a comparative analysis of reported cases and global burden of disease study, 2010-2019

BACKGROUND

Dengue is a significant mosquito-borne disease. Several studies have utilized estimates from the Global Burden of Disease (GBD) study to assess the global, regional or national burden of dengue over time. However, our recent investigation suggests that GBD's estimates for dengue cases in Taiwan are unrealistically high. The current study extends the scope to compare reported dengue cases with GBD estimates across 30 high-burden countries and territories, aiming to assess the accuracy and interpretability of the GBD's dengue estimates.

METHODS

Data for this study were sourced from the GBD 2019 study and various national and international databases documenting reported dengue cases. The analysis targeted the top 30 countries and territories with the highest 10-year average of reported cases from 2010 to 2019. Discrepancies were quantified by computing absolute differences and ratios between the 10-year average of reported cases and GBD estimates. Coefficients of variation (CV) and estimated annual percentage changes (EAPCs) were calculated to assess variations and trends in the two data sources.

RESULTS

Significant discrepancies were noted between reported data and GBD estimates in the number of dengue cases, incidence rates, and EAPCs. GBD estimates were substantially higher than reported cases for many entities, with the most notable differences found in China (570.0-fold), India (303.0-fold), Bangladesh (115.4-fold), Taiwan (85.5-fold) and Indonesia (23.2-fold). Furthermore, the GBD's estimates did not accurately reflect the extensive yearly fluctuations in dengue outbreaks, particularly in non-endemic regions such as Taiwan, China and Argentina, as evidenced by high CVs.

CONCLUSIONS

This study reveals substantial discrepancies between GBD estimates and reported dengue cases, underscoring the imperative for comprehensive analysis in areas with pronounced disparities. The failure of GBD estimates to represent the considerable annual fluctuations in dengue outbreaks highlights the critical need for improvement in disease burden estimation methodologies for dengue.

The epidemiologic and economic burden of dengue in Singapore: A systematic review

BACKGROUND

Despite its well-regarded vector control program, Singapore remains susceptible to dengue epidemics. To assist evaluation of dengue interventions, we aimed to synthesize current data on the epidemiologic and economic burden of dengue in Singapore.

METHODOLOGY

We used multiple databases (PubMed, Embase, Cochrane, international/national repositories, surveillance) to search for published and gray literature (2000-2022). We included observational and cost studies, and two interventional studies, reporting Singapore-specific data on our co-primary outcomes, dengue incidence and dengue-related costs. Quality was assessed using the Newcastle-Ottawa Scale and an adapted cost-of-illness evaluation checklist. We performed a narrative synthesis and grouped studies according to reported outcomes and available stratified analyses.

FINDINGS

In total, 333 reports (330 epidemiological, 3 economic) were included. Most published epidemiological studies (89%) and all economic studies were of good quality. All gray literature reports were from the Ministry of Health or National Environment Agency. Based predominantly on surveillance data, Singapore experienced multiple outbreaks in 2000-2021, attaining peak incidence rate in 2020 (621.1 cases/100,000 person-years). Stratified analyses revealed the highest incidence rates in DENV-2 and DENV-3 serotypes and the 15-44 age group. Among dengue cases, the risk of hospitalization has been highest in the ≥45-year-old age groups while the risks of dengue hemorrhagic fever and death have generally been low (both <1%) for the last decade. Our search yielded limited data on deaths by age, severity, and infection type (primary, secondary, post-secondary). Seroprevalence (dengue immunoglobulin G) increases with age but has remained <50% in the general population. Comprising 21-63% indirect costs, dengue-related total costs were higher in 2010-2020 (SGD 148 million) versus the preceding decade (SGD 58-110 million).

CONCLUSION

Despite abundant passive surveillance data, more stratified and up-to-date data on the epidemiologic and economic burden of dengue are warranted in Singapore to continuously assess prevention and management strategies.

Efficacy of Wolbachia-mediated sterility to reduce the incidence of dengue: a synthetic control study in Singapore

BACKGROUND

Due to the absence of available therapeutics and good vaccines, vector control solutions are needed to mitigate the spread of dengue. Matings between male Aedes aegypti mosquitoes infected with the wAlbB strain of Wolbachia and wildtype females yield non-viable eggs. We evaluated the efficacy of releasing wAlbB-infected A aegypti male mosquitoes to suppress dengue incidence.

METHODS

In this synthetic control study, we conducted large-scale field trials in Singapore involving release of wAlbB-infected A aegypti male mosquitoes for dengue control via vector population suppression, from epidemiological week (EW) 27, 2018, to EW 26, 2022. We selected two large towns (Yishun and Tampines) to adopt an expanding release strategy and two smaller towns (Bukit Batok and Choa Chu Kang) to adopt a targeted-release approach. Releases were conducted two times a week in high-rise public housing estates. All intervention and control locations practised the same baseline dengue control protocol. The main outcome was weekly dengue incidence rate caused by any dengue virus serotype. We used incidence data collected by the Singapore Ministry of Health to assess the efficacy of the interventions. To compare interventions, we used the synthetic control method to generate appropriate counterfactuals for the intervention towns using a weighted combination of 30 control towns between EW 1, 2014 and EW 26, 2022.

FINDINGS

Our study comprised an at-risk population of 607 872 individuals living in intervention sites and 3 894 544 individuals living in control sites. Interventions demonstrated up to 77·28% (121/156, 95% CI 75·81-78·58) intervention efficacy despite incomplete coverage across all towns until EW 26, 2022. Intervention efficacies increased as release coverage increased across all intervention sites. Releases led to 2242 (95% CI 2092-2391) fewer cases per 100 000 people in intervention sites during the study period. Secondary analysis showed that these intervention effects were replicated across all age groups and both sexes for intervention sites.

INTERPRETATION

Our results demonstrated the potential of Wolbachia-mediated incompatible insect technique for strengthening dengue control in tropical cities, where dengue burden is the greatest.

FUNDING

Singapore Ministry of Finance, Ministry of Sustainability, and the National Environment Agency, and the Singapore National Robotics Program.

Precision Prediction for Dengue Fever in Singapore: A Machine Learning Approach Incorporating Meteorological Data

OBJECTIVE

This study aimed to improve dengue fever predictions in Singapore using a machine learning model that incorporates meteorological data, addressing the current methodological limitations by examining the intricate relationships between weather changes and dengue transmission.

METHOD

Using weekly dengue case and meteorological data from 2012 to 2022, the data was preprocessed and analyzed using various machine learning algorithms, including General Linear Model (GLM), Support Vector Machine (SVM), Gradient Boosting Machine (GBM), Decision Tree (DT), Random Forest (RF), and eXtreme Gradient Boosting (XGBoost) algorithms. Performance metrics such as Mean Absolute Error (MAE), Root Mean Square Error (RMSE), and R-squared (R2) were employed.

RESULTS

From 2012 to 2022, there was a total of 164,333 cases of dengue fever. Singapore witnessed a fluctuating number of dengue cases, peaking notably in 2020 and revealing a strong seasonality between March and July. An analysis of meteorological data points highlighted connections between certain climate variables and dengue fever outbreaks. The correlation analyses suggested significant associations between dengue cases and specific weather factors such as solar radiation, solar energy, and UV index. For disease predictions, the XGBoost model showed the best performance with an MAE = 89.12, RMSE = 156.07, and R2 = 0.83, identifying time as the primary factor, while 19 key predictors showed non-linear associations with dengue transmission. This underscores the significant role of environmental conditions, including cloud cover and rainfall, in dengue propagation.

CONCLUSION

In the last decade, meteorological factors have significantly influenced dengue transmission in Singapore. This research, using the XGBoost model, highlights the key predictors like time and cloud cover in understanding dengue's complex dynamics. By employing advanced algorithms, our study offers insights into dengue predictive models and the importance of careful model selection. These results can inform public health strategies, aiming to improve dengue control in Singapore and comparable regions.

Chikungunya: a decade of burden in the Americas

In the Americas, one decade following its emergence in 2013, chikungunya virus (CHIKV) continues to spread and cause epidemics across the region. To date, 3.7 million suspected and laboratory-confirmed chikungunya cases have been reported in 50 countries or territories in the Americas. Here, we outline the current status and epidemiological aspects of chikungunya in the Americas and discuss prospects for future research and public health strategies to combat CHIKV in the region.

Facing the escalating burden of dengue: Challenges and perspectives

Dengue is the most rapidly emerging mosquito-borne infection and, due to climate change and unplanned urbanization, it is predicted that the global burden of dengue will rise further as the infection spreads to new geographical locations. Dengue-endemic countries are often unable to cope with such increases, with health care facilities becoming overwhelmed during each dengue season. Furthermore, although dengue has been predominantly a childhood illness in the past, it currently mostly affects adults in many countries, with higher incidence of severe disease and mortality rates in pregnant women and in those with comorbidities. As there is currently no specific treatment for dengue and no early biomarker to identify those who will progress to develop vascular leakage, all individuals with dengue are closely monitored in case they need fluid management. Furthermore, diagnosing patients with acute dengue is challenging due to the similarity of clinical symptoms during early illness and poor sensitivity and specificity of point-of-care diagnostic tests. Novel vector control methods, such as the release of Wolbachia-infected mosquitoes, have shown promising results by reducing vector density and dengue incidence in clinical trial settings. A new dengue vaccine, TAK-003, had an efficacy of 61.2% against virologically confirmed dengue, 84.1% efficacy against hospitalizations and a 70% efficacy against development of dengue haemorrhagic fever (DHF) at 54 months. While vaccines and mosquito control methods are welcome, they alone are unlikely to fully reduce the burden of dengue, and a treatment for dengue is therefore essential. Several novel antiviral drugs are currently being evaluated along with drugs that inhibit host mediators, such as mast cell products. Although viral proteins such as NS1 contribute to the vascular leak observed in severe dengue, the host immune response to the viral infection also plays a significant role in progression to severe disease. There is an urgent need to discover safe and effective treatments for dengue to prevent disease progression.

Associations between Dengue Incidence, Ecological Factors, and Anthropogenic Factors in Singapore

Singapore experiences endemic dengue. Vector control remains the primary means to reduce transmission due to the lack of available therapeutics. Resource limitations mean that vector-control tools need to be optimized, which can be achieved by studying risk factors related to disease transmission. We developed a statistical modelling framework which can account for a high-resolution and high-dimensional set of covariates to delineate spatio-temporal characteristics that are associated with dengue transmission from 2014 to 2020 in Singapore. We applied the proposed framework to two distinct datasets, stratified based on the primary type of housing within each spatial unit. Generalized additive models reveal non-linear exposure responses between a large range of ecological and anthropogenic factors as well as dengue incidence rates. At values below their mean, lesser mean total daily rainfall (Incidence rate ratio (IRR): 3.75, 95% CI: 1.00-14.05, Mean: 4.40 mm), decreased mean windspeed (IRR: 3.65, 95% CI: 1.87-7.10, Mean: 4.53 km/h), and lower building heights (IRR: 2.62, 95% CI: 1.44-4.77, Mean: 6.5 m) displayed positive associations, while higher than average annual NO2 concentrations (IRR: 0.35, 95% CI: 0.18-0.66, Mean: 13.8 ppb) were estimated to be negatively associated with dengue incidence rates. Our study provides an understanding of associations between ecological and anthropogenic characteristics with dengue transmission. These findings help us understand high-risk areas of dengue transmission, and allows for land-use planning and formulation of vector control policies.