Abstract
Present study reports an unprecedented dengue outbreak in Taiwan post-COVID-19. Interrupted time series analysis reveals a significant surge after easing restrictions, emphasizing the roles of COVID-19 measures, especially travel restrictions, international transportation and climate change in the epidemic. Preventing and controlling dengue remain substantial challenges in the post-COVID-19 era.
The epidemiology of infectious diseases has undergone significant changes during the COVID-19 pandemic.1 Numerous regions implemented stringent control measures, including lockdowns, non-pharmaceutical interventions and restrictions on international transportation. These strategies profoundly impacted the transmission of SARS-CoV-2 and other infectious diseases with droplet transmission, such as influenza.1 The resurgence of infectious diseases after the relaxation of these restrictive measures has been observed, emphasizing the importance of preventing and controlling re-emerging diseases in the post-COVID-19 era.2
Dengue, a vector-borne disease transmitted by Aedes aegypti and Aedes albopictus mosquitoes, is endemic in many areas.3 International transportation plays a significant role in the spread of dengue in various regions, and outbreaks of imported cases are not uncommon. During the COVID-19 pandemic, reported dengue cases also declined with the reduction in international travel.4 While Taiwan did not implement a strict lockdown, it adopted several public health strategies to control the spread of COVID-19, including border control. These restrictive measures were gradually eased, and the lifting of border controls was initiated in October 2022. The pandemic level decreased by May 2023, and the World Health Organization officially declared the end of COVID-19 public health emergency of international concern in the same month. The impact of changes in public health measures and the resumption of international transportation on dengue prevalence remain largely unclear. We are now reporting an unprecedented dengue outbreak in Taiwan following the COVID-19 pandemic.
Dengue is a communicable disease in Taiwan, and all suspected and confirmed cases are reported to the Taiwan Centers for Disease Control.5 We have extracted dengue cases from the database since 2018 and the number of inbound visitors from the database of Tourism Administration to investigate the possible correlation between international transportation and dengue cases.5,6 Furthermore, climate change is an important factor in dengue prevalence, and we conducted an investigation into temperature and precipitation data obtained from the Central Weather Administration to explore potential correlations between dengue cases and climate changes.7 We also performed interrupted time series analysis employing segmented regression with Prais–Winsten regression to assess the impact of policy change on dengue prevalence. Our study has received approval from the institutional review board (MacKay Memorial Hospital, Protocol Number: 20MMHIS140e).
First and foremost, we have observed an unprecedented dengue outbreak in Taiwan following the easing of COVID-19 restrictive strategies (Figure 1). During the pandemic, there was a substantial reduction in international transportation, resulting in only sporadic imported cases. However, with the gradual relaxation of stringent measures, lifting of border control, and the downgrade of the pandemic alert level since May 2023, we witnessed a significant increase in imported cases, swiftly followed by an exponential rise in local cases. This finding underscores the crucial role of imported cases in driving the epidemic. The monthly incidence of both imported and locally acquired dengue cases is delineated in Supplementary Table 1 available as Supplementary data at JTM online. To examine the influence of changes in public health strategy on dengue prevalence, we performed an interrupted time series analysis employing segmented regression with Prais-Winsten regression (Supplementary Figure 1 available as Supplementary data at JTM online). The red dash-dotted line signifies the relaxation of public health strategies against COVID-19, and a significant upswing in dengue cases (black line) was noted after May 2023. The orange dashed line illustrates the hypothetical counterfactual trend in the absence of policy changes and the reopening of international transportation. The blue dashed line depicts the actual trend following the policy change. On average, there were 22.6 monthly cases before the implementation of the policy change, which surged to 3666.7 monthly cases thereafter. This marked escalation, accounting to an increase of 1284 monthly cases post-policy change, deserves careful consideration.
Figure 1.
Number of (A) imported and local dengue cases; (B) inbound visitors and dengue cases in Taiwan between 2020 and 2023 (A) Sporadic imported cases were observed before policy change. A sharp increase in imported cases following the lifting of restrictions, subsequently fueling a surge in local cases. (B) COVID-19 restrictive measures were gradually eased since late 2022, resulting in a significant increase in inbound visitors. An exponential rise in dengue cases swiftly followed. This figure underscores the critical role of globalization, particularly international importation, in the prevention and control of dengue. PHEIC: Public health emergency of international concern
Furthermore, our observations suggest that international transportation and climate change may also impact the dengue epidemic. We found a moderate correlation between dengue cases and inbound visitors and maximal temperatures (Supplementary Figure 2 and Supplementary Table 2 available as Supplementary data at JTM online, with Pearson correlation coefficients of 0.475 and 0.332, with P-values <0.05). However, we did not identify significant correlations between average temperature, minimal temperature, precipitation quantities, precipitation days, and dengue cases. Further multiple regression analyses showed similar results (R2 0.317, F test 9.963, P<0.01).
Dengue remains a substantial health threat with a global estimate of 390 million infections annually, and a resurgence of dengue after COVID-19 has been reported in many areas.2 For example, an unprecedented outbreak of dengue occurred in Nepal with more than 50 000 cases and 50 deaths in 2022.2 A serious dengue outbreak was reported in Bangladesh in 2023.8 Approximately half of the world's population resides in areas at risk of dengue, and documented cases of dengue importation into non-endemic countries have occurred. Our study indicates the potential role of the easing of COVID-19 restrictions and the resumption of international transportation in the spread of dengue. Furthermore, climate change has also had a significant impact on the incidence of dengue, and a previous study showed mosquito gene expression, bacterial microbiome, and viral population diversity may be heavily altered by temperatures.9 Therefore, global warming and heatwaves increased the transmission of the disease.8 Our study aligns with previous research, revealing a moderate correlation between maximal temperature and dengue cases. Global warming and climate change have a steady impact on dengue prevalence, and the easing of public health strategies and the resumption of international transportation may also have an impact on dengue outbreaks. Vaccination is the best strategy to prevent and control dengue, but an effective vaccine is not widely available at present.10 Prevention and control of dengue outbreaks require multifaceted approaches and remain a rigorous challenge after the COVID-19 pandemic.
Our study leverages the robustness of the national surveillance database; nonetheless, certain limitations warrant consideration. Firstly, given that dengue in Taiwan is a communicable disease, its diagnosis relies on serological tests. While the potential for under-reporting exists, the noteworthy surge in cases subsequent to the policy change demands our scrutiny. Secondly, dengue constitutes a complex health issue influenced by various health, meteorological, socio-economic factors, host immunity, and circulating virus genotypes. Consequently, establishing a causal relationship between policy changes and dengue incidence necessitates further in-depth investigation.
In conclusion, we report an unprecedented outbreak of dengue in Taiwan after the easing of COVID-19 restrictive strategies. Interrupted time series analysis demonstrated a significant increase after lifting restrictions. Our study highlights the critical roles of international transportation and climate change in the dengue epidemic. Measures taken to combat COVID-19, particularly international travel restrictions, likely played a role in controlling the dengue epidemic. Effectively preventing and controlling dengue presents a substantial challenge in the post-COVID-19 era.
Funding
The authors declare no funding.
Author contributions
NCC and CYL were responsible for conception and draft writing. SLW and HC performed critical review and literature search. All authors involved in data collection, analysis, and approved the final manuscript.
Conflict of interests: The authors declare no conflict of interest.
Supplementary Material
Contributor Information
Nan-Chang Chiu, Department of Pediatrics, MacKay Children’s Hospital, Taipei, Taiwan; Department of Medicine, MacKay Medical College, New Taipei, Taiwan.
Hsin Chi, Department of Pediatrics, MacKay Children’s Hospital, Taipei, Taiwan; Department of Medicine, MacKay Medical College, New Taipei, Taiwan.
Shun-Long Weng, Department of Medicine, MacKay Medical College, New Taipei, Taiwan; Department of Pediatrics and Obstetrics & Gynecology, Hsinchu Municipal MacKay Children’s Hospital, Hsinchu, Taiwan; Department of Pediatrics and Obstetrics & Gynecology, Hsinchu MacKay Memorial Hospital, Hsinchu, Taiwan.
Chien-Yu Lin, Department of Medicine, MacKay Medical College, New Taipei, Taiwan; Department of Pediatrics and Obstetrics & Gynecology, Hsinchu Municipal MacKay Children’s Hospital, Hsinchu, Taiwan; Department of Pediatrics and Obstetrics & Gynecology, Hsinchu MacKay Memorial Hospital, Hsinchu, Taiwan.
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