Abstract
Southern Thailand has been experiencing a large chikungunya virus (CHIKV) outbreak since October 2018. Given the magnitude and duration of the outbreak and its location in a popular tourist destination, we sought to determine international case exportation risk and identify countries at greatest risk of receiving travel-associated imported CHIKV cases. We used a probabilistic model to estimate the expected number of exported cases from Southern Thailand between October 2018 and April 2019. The model incorporated data on CHIKV natural history, infection rates in Southern Thailand, average length of stay for tourists, and international outbound air passenger numbers from the outbreak area. For countries highly connected to Southern Thailand by air travel, we ran 1000 simulations to estimate the expected number of imported cases. We also identified destination countries with conditions suitable for autochthonous CHIKV transmission. Over the outbreak period, we estimated that an average of 125 (95% credible interval (CrI): 102–149) cases would be exported from Southern Thailand to international destinations via air travel. China was projected to receive the most cases (43, 95% CrI: 30–56), followed by Singapore (7, 95% CrI: 2–12) and Malaysia (5, 95% CrI: 1–10). Twenty-three countries were projected to receive at least one imported case, and 64% of these countries had one or more regions that could potentially support autochthonous CHIKV transmission. The overall risk of international exportation of CHIKV cases associated with the outbreak is Southern Thailand is high. Our model projections are consistent with recent reports of CHIKV in travelers returning from the region. Countries should be alert to the possibility of CHIKV infection in returning travelers, particularly in regions where autochthonous transmission is possible.
Highlights
Chikungunya virus (CHIKV) is an arbovirus transmitted to humans by the bite of infected Aedes mosquitoes (Evans and Kaslow, 1997)
To date, reported rates of CHIKV infection during the current outbreak were highest in December 2018
Between October 2017 and April 2018, there was an average of 649,907 monthly outbound passengers departing from airports in Southern Thailand, with the greatest number of travelers departing in March
Summary
Chikungunya virus (CHIKV) is an arbovirus transmitted to humans by the bite of infected Aedes mosquitoes (Evans and Kaslow, 1997). The first reported cases of CHIKV infection in Thailand were in 1958 (Hammon, Rudnick, & Sather, 1960), and sporadic cases and outbreaks have been reported throughout the country since that time (Rianthavorn et al, 2010; Thaikruea et al, 1997). In 2008e2010, there was a large outbreak that was first reported in Narathiwat province in the south of the country, near the Malaysian border (Rianthavorn et al, 2010). The outbreak eventually spread to more than one-third of districts across Thailand and was associated with the novel introduction of the East Central and South African lineage to the country (Chadsuthi et al, 2018). A subsequent serosurvey conducted in 2014 demonstrated the wide extent of CHIKV transmission in the southern provinces of Trang and Narathiwat, where age-standardized seroprevalence was estimated at 29.6% (Vongpunsawad, Intharasongkroh, Thongmee, & Poovorawan, 2017)
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