The epidemiology of imported and locally acquired dengue in Australia, 2012-2022

Abstract

Background: Dengue is the most important arboviral disease globally and poses ongoing challenges for control including in non-endemic countries with competent mosquito vectors at risk of local transmission through imported cases. We examined recent epidemiological trends in imported and locally acquired dengue in Australia, where the Wolbachia mosquito population replacement method was implemented throughout dengue-prone areas of northern Queensland between 2011 and 2019.

Methods: We analysed dengue cases reported to the Australian National Notifiable Disease Surveillance System between January 2012 and December 2022, and Australian traveller movement data.

Results: Between 2012 and 2022, 13 343 dengue cases were reported in Australia (median 1466 annual cases); 12 568 cases (94.2%) were imported, 584 (4.4%) were locally acquired and 191 (1.4%) had no origin recorded. Locally acquired cases decreased from a peak in 2013 (n = 236) to zero in 2021-22. Annual incidence of imported dengue ranged from 8.29/100 000 (n = 917 cases) to 22.10/100 000 (n = 2203) annual traveller movements between 2012 and 2019, decreased in 2020 (6.74/100 000 traveller movements; n = 191) and 2021 (3.32/100 000 traveller movements; n = 10) during COVID-19-related border closures, then rose to 34.79/100 000 traveller movements (n = 504) in 2022. Imported cases were primarily acquired in Southeast Asia (n = 9323; 74%), Southern and Central Asia (n = 1555; 12%) and Oceania (n = 1341; 11%). Indonesia (n = 5778; 46%) and Thailand (n = 1483; 12%) were top acquisition countries. DENV-2 (n = 2147; 42%) and DENV-1 (n = 1526; 30%) were predominant serotypes.

Conclusion: Our analysis highlights Australia's successful control of locally acquired dengue with Wolbachia. Imported dengue trends reflect both Australian travel destinations and patterns and local epidemiology in endemic countries.

Keywords: Infectious disease; arbovirus; imported infection; notifiable disease; surveillance; travel.

Figure 1

Number of locally acquired dengue cases and dengue serotype, Australia 2012–22. *Pilot releases of Wolbachia mosquitoes in two suburbs of Cairns occurred in 2011, followed by phased releases across urban areas of northern Queensland in 2013–2019^,

Figure 2

Number and notification incidence of imported dengue cases, Australia 2012–22. Abbreviations: STRR: short-term resident return; SE: Southeast. Vertical bars depict the number of cases by region and use the left y-axis, while the lines depict the overall (solid line) and regional (dotted line) notification incidences per 100 000 STRR trips and use the right y-axis. All other regions include Northwest Europe, Southern and Eastern Europe, North Africa and the Middle East, Sub-Saharan Africa, Northeast Asia

Figure 3

Top 10 countries of acquisition by DENV serotype for imported dengue cases, 2012–22. Abbreviations: DENV: Dengue virus. Ranking is based on number of cases imported from each country

Figure 4

Lowest, highest and average incidence (per 100 000 traveller movements) for top countries of acquisition, 2012–19. Abbreviations: STRR: short-term resident return. STRR trips are obtained for each country from ABS data. Data for Timor-Leste not available. Average data for 2012 to 2019 only included as expected decreases in incidence occurred in 2020 following implementation of travel restrictions due to the COVID-19 pandemic

Figure 5

Estimated notification incidence of imported dengue in returned Australian travellers and estimated local incidence of dengue for countries of interest, 2012–22. Abbreviations: STRR: Short term resident return. The solid line represents the incidence in returned travellers and follows the left y-axis. The dashed line represents country specific local incidence and follows the right y-axis. Country-specific dengue case data derived from surveillance data for Indonesia, Thailand, India, Sri Lanka, Malaysia, Vietnam, The Philippines. Local incidence data for Fiji obtained from surveillance reports (Appendix, Table S1) and the literature. Data for local dengue cases not available for 2015 for Fiji. Data for local dengue cases not available for 2020 for Fiji. Data for local dengue cases not available for 2021 for Fiji. Data for local dengue cases not available for 2022 for Indonesia, Sri Lanka, Fiji. Data for local dengue cases for Vietnam available until 19th November 2020, 19th December 2021 and 12th December 2022. National dengue data not available for PNG or Timor-Leste. Traveller movement data not available for Timor-Leste. Singapore included given its status as the only other dengue endemic country in the top ten most frequented travel destinations (Appendix, Table S4).