We conducted a retrospective, multicountry ecological study analyzing trends in dengue incidence in 7 Southeast Asian countries from January 2000 to December 2023. Data on annual dengue cases were extracted from the following sources: (1) the World Health Organization (WHO) Global Health Observatory data repository [19], (2) the national centers for disease control and prevention of the respective countries, and (3) the ministry of health databases of the selected countries [19-26]. We first screened the WHO Global Health Observatory database to identify countries with available annual dengue incidence data [27]. Subsequently, we cross-validated the data with official national sources, including the websites of ministries of health or national centers for disease control. Countries with data that were incomplete, inconsistent, or not publicly available were excluded from the final analysis. In parallel, we retrieved national annual average temperature trends from publicly accessible climate databases [28]. A flowchart detailing the country selection process is provided in Multimedia Appendix 1.

For each country, we compiled the annual number of reported dengue cases and population estimates to calculate incidence rates. Crude dengue incidence rates (cases per 100,000 population) were calculated by dividing the annual number of reported cases by the corresponding national population estimates, allowing for cross-country comparability. Population data were obtained from the publicly available United Nations demographic database [29]. Further standardization by age and sex was not performed, as the primary objective of this study was to assess overall national dengue incidence. In cases of data discrepancies between sources, national health authority reports were prioritized, followed by WHO data. Cross-verification between multiple sources was conducted for validation and quality control by 2 authors independently. Dengue is a notifiable communicable disease in all countries included in this study. We used Taiwan as an example, where the diagnosis of dengue is based on a combination of clinical, epidemiological, and laboratory criteria. Genetic typing is performed in specific scenarios, such as the identification of index cases in endemic regions or during outbreak investigations. Confirmed cases are further classified as either imported or locally acquired. In this study, both imported and local cases in Taiwan were included to characterize the composition of reported dengue cases. In addition, national annual average temperature data during the study period were retrieved from publicly accessible meteorological databases.

Statistical analyses were performed using R statistical software (version 4.1.0). Annual incidence rates per 100,000 population were calculated for each country, and epidemiological trends were visualized using the ggplot2 package. Linear regression models were applied to assess the trends in dengue incidence over time, with the model specified as Y=β0+β1X+ϵ, where Y is the annual dengue incidence, X is the year, β0 is the intercept, β1 is the slope, and ϵ is the error term. Model parameters, including the slope and R² values, were evaluated to determine the direction and strength of the trends. A P value less than .05 was considered statistically significant.

This study was conducted in accordance with the ethical standards of the Declaration of Helsinki [30]. Our study was approved by the institutional review board of MacKay Memorial Hospital, Taipei, Taiwan (20MMHIS140e). This study used publicly available, aggregated data and did not involve individual patient information. We adhered to the principles of ethical research practice throughout the study.

The disease burden of dengue is unquestionably substantial. Our study elucidates the epidemiological changes in an endemic region over a 24-year period. Despite advances in public health, we observed a significant increase in dengue incidence in several Southeast Asian countries, including the Philippines, Vietnam, Malaysia, and Singapore. Other countries demonstrated relatively stable endemic patterns. While dengue cases declined during the COVID-19 pandemic, a notable resurgence was observed across all studied countries, underscoring dengue’s continued significance as a critical public health threat in the postpandemic era.

A marked nadir in dengue incidence was observed during the COVID-19 pandemic. Public health strategies, implementation of nonpharmaceutical interventions, and social and international restrictions likely contributed to this observed reduction. In Sri Lanka, for instance, national dengue case numbers significantly decreased during lockdown periods [31]. In Australia, dengue cases nearly disappeared during the pandemic [32]. Our study revealed that Thailand, Cambodia, and Taiwan reported fewer than 30 cases per 100,000 inhabitants during this period. However, the apparent decrease in reported dengue cases may be attributable to underreporting due to several factors: inadequate medical resources, compromised communication systems, limited diagnostic capabilities, and reduced health care–seeking behavior. Most dengue infections present with mild symptoms such as fever, headache, arthralgia, and skin rashes, and individuals with mild illness may have been less likely to seek medical attention due to reduced health care services and concerns about potential COVID-19 exposure. Additionally, health care providers were primarily focused on COVID-19 diagnostics, potentially leading to decreased dengue screening and testing. During the COVID-19 pandemic, neither the virus nor vector-borne mosquitoes disappeared; instead, they remained latent within communities, waiting for opportunities to resurface. In the aftermath of the COVID-19 pandemic, an “immune debt” phenomenon has emerged, leading to the resurgence of numerous infectious diseases, including influenza, enterovirus, respiratory syncytial virus, and dengue fever. Multiple countries, such as Brazil, Australia, Egypt, and Taiwan, have experienced significant dengue fever outbreaks following the relaxation of pandemic-related restrictions [32-37]. Our research has uncovered similar trends: during the COVID-19 pandemic, stringent preventive measures and reduced international travel disrupted typical epidemiological patterns. Consequently, the health threat posed by dengue fever remains a critical public health concern in the postpandemic era.

Climate change and global warming may contribute to the expanded distribution of vector mosquitoes and increased dengue incidence [11,12,35,38-41]. The optimal temperature for Aedes albopictus and Aedes aegypti is approximately 25 °C to 30 °C [10]. Warmer temperatures can shorten viral replication incubation periods in mosquitoes, accelerate mosquito growth, and increase biting frequency. Our study showed an overall temperature increase ranging from 0.97 °C to 2.22 °C. Consequently, climate change may expand vector habitat ranges and potentially increase infection transmission zones. Theoretically, dengue is more prevalent in tropical regions. Our study showed a relatively lower incidence in Taiwan, a subtropical country. However, dengue prevalence is influenced by multiple complex factors. We found that the dengue incidence rates significantly increased over the study period in the Philippines, Vietnam, Malaysia, and Singapore. However, these countries were not those with the lowest latitudes or the highest average temperatures among the study sample. Urbanization may reduce breeding sites, alter water accumulation patterns, and impact vector proliferation. Population density and international travel resumption potentially contribute to disease spread [42]. Interestingly, some research has explored correlations between economic indicators like gross domestic product (GDP) and dengue transmission, though findings remain inconsistent [43,44]. Countries with lower GDP often have limited investment in public health infrastructure, medical services, and vector control programs, which may contribute to higher dengue transmission. Conversely, widespread dengue outbreaks may negatively impact national economies by reducing tourism revenue and workforce productivity, thereby further decreasing GDP. In brief, the incidence of dengue epidemics is fueled by multiple complex factors [45,46]. Data from the past 24 years indicate that these evolving trends cannot be explained by any single factor alone.

Our study possesses notable strengths, primarily stemming from its comprehensive analysis of national databases that systematically tracked epidemiological trends across 7 countries over an extensive 24-year period, encompassing both pre- and post–COVID-19 pandemic epochs. However, the research is not without limitations. The study was unable to comprehensively characterize the severity of dengue infections, which range from asymptomatic to severe. Moreover, multiple complex and potentially influential factors remained unaccounted for in this analysis, including nuanced variations in climate patterns, urbanization levels, international travel dynamics, economic indicators, and vaccination status. These unexamined variables could potentially modulate dengue transmission in ways not fully captured by our current methodological approach. Due to the unavailability of reliable data, several countries were excluded from the final analysis. Consequently, while our findings provide valuable insights into regional dengue epidemiology, they also underscore the necessity for future research that can more comprehensively integrate these multifaceted determinants of disease transmission.

Our 24-year epidemiological analysis of dengue fever in Southeast Asia reveals the complex dynamics of disease transmission. The COVID-19 pandemic temporarily disrupted transmission patterns, but the subsequent resurgence highlights the virus’s resilience. Ongoing, multicountry surveillance efforts are essential for the effective prevention and control of dengue.