A threshold analysis of dengue transmission in terms of weather variables and imported dengue cases in Australia

Abstract

Dengue virus (DENV) transmission in Australia is driven by weather factors and imported dengue fever (DF) cases. However, uncertainty remains regarding the threshold effects of high-order interactions among weather factors and imported DF cases and the impact of these factors on autochthonous DF. A time-series regression tree model was used to assess the threshold effects of natural temporal variations of weekly weather factors and weekly imported DF cases in relation to incidence of weekly autochthonous DF from 1 January 2000 to 31 December 2009 in Townsville and Cairns, Australia. In Cairns, mean weekly autochthonous DF incidence increased 16.3-fold when the 3-week lagged moving average maximum temperature was <32 °C, the 4-week lagged moving average minimum temperature was ≥24 °C and the sum of imported DF cases in the previous 2 weeks was >0. When the 3-week lagged moving average maximum temperature was ≥32 °C and the other two conditions mentioned above remained the same, mean weekly autochthonous DF incidence only increased 4.6-fold. In Townsville, the mean weekly incidence of autochthonous DF increased 10-fold when 3-week lagged moving average rainfall was ≥27 mm, but it only increased 1.8-fold when rainfall was <27 mm during January to June. Thus, we found different responses of autochthonous DF incidence to weather factors and imported DF cases in Townsville and Cairns. Imported DF cases may also trigger and enhance local outbreaks under favorable climate conditions.

Keywords:

• Aedes aegypti
• autochthonous dengue
• classification and regression tree
• dengue fever
• imported dengue

Acknowledgments

We thank National Health and Medical Research Council in Australia for funding (#1002608) this study. We also thank the Queensland Department of Health, Australian Bureau of Meteorology and Australian Bureau of Statistics for providing the data on notified dengue fever cases, climate and population growth, respectively.

Notes

ADF: autochthonous DF cases.

IMDF: imported DF cases.

MinT: minimum temperature.

MaxT: maximum temperature.

RH: relative humidity at minimum temperature.

SEM : standard error of mean.