Spatial incidence of dengue infections in Queensland, Australia - reply

The authors reply

We appreciate the letter by Ritchie et al. as well as the extensive contribution they have made to dengue fever surveillance and control in Australia. With regard to their concern about the methodology used in our study [1], we respond as follows: (i) The primary objective of our paper was to examine the overall spatiotemporal pattern of notified dengue cases in Queensland over the last two decades. We stated upfront that both imported and locally acquired cases were included in data analysis and display ([1], p. 392]). Because the differentiation between imported and locally acquired cases has only been made in the Queensland dengue surveillance system (notifiable conditions register) since 2001, it was impossible to separate them in this 12 year time-series analysis. (ii) Our research showed a change in the spatial patterns of dengue (both imported and locally acquired) which is significant in terms of assessing dengue risk and planning resource allocation. An increase in imported cases south of Townsville is still important and it has the potential to cause dengue outbreaks because of the existence of Aedes aegypti mosquitoes in this region. (iii) Imported cases of dengue need to be monitored more closely because the number of imported dengue cases might also reflect the level of dengue transmission in endemic countries and appropriate and prompt warning should be given to travellers by the Australian government. The global geographical range of dengue has been rapidly expanding [2], and dengue fever and its vectors can cross international boundaries through international travel, migration and trade [3], making imported case surveillance of utmost importance. (iv) We have conducted other studies that showed a relationship between climate variability and dengue incidence (both imported and locally acquired), and there is other literature presenting concordant results [4], so the statement regarding an association between climate fluctuation and dengue transmission is supported [5, 6].