Multiple outbreaks of dengue serotype 2 in north Queensland, 2003/04

Objectives: To describe the various investigations and responses to multiple outbreaks of dengue serotype 2 that occurred in north Queensland in 2003/04. Methods: Details about each case were collated so as to target mosquito-control responses including control of mosquito breeding sites, interior spraying of selected premises, and a novellure and kill' approach using lethal ovitraps. Phylogenetic analyses were undertaken to determine the genetic relatedness of viruses isolated during the outbreaks. Results: Except for a two-month hiatus in mid-2003, the outbreaks continued for 16 months and included similar to 900 confirmed cases, with three severe cases and one death. The available evidence suggests that the mosquito-control measures were effective, but delays in recognising the outbreaks in Cairns and the Torres Strait coupled with intense mosquito breeding contributed to the extensive nature of the outbreaks. Phylogenetic analyses showed that there had been only two major outbreaks, one that spread from Cairns to Townsville, the other from the Torres Strait to Cairns; both were initiated by viraemic travellers from Papua New Guinea. Conclusions: Phylogenetic analyses were essential in understanding how the outbreaks were related to each other, and in demonstrating that dengue had not become endemic. Further innovative approaches to dengue surveillance and mosquito control in north Queensland are necessary. Implications: Dengue outbreaks have become more frequent and more severe in north Queensland in recent years, raising the possibility that dengue viruses could become endemic in the region leading to outbreaks of dengue haemorrhagic fever.