Abstract
The development of visual tools for the timely identification of spatio-temporal clusters will assist in implementing control measures to prevent further damage. From January 2015 to June 2020, a total number of 1463 avian influenza outbreak farms were detected in Taiwan and further confirmed to be affected by highly pathogenic avian influenza subtype H5Nx. In this study, we adopted two common concepts of spatio-temporal clustering methods, the Knox test and scan statistics, with visual tools to explore the dynamic changes of clustering patterns. Since most (68.6%) of the outbreak farms were detected in 2015, only the data from 2015 was used in this study. The first two-stage algorithm performs the Knox test, which established a threshold of 7 days and identified 11 major clusters in the six counties of southwestern Taiwan, followed by the standard deviational ellipse (SDE) method implemented on each cluster to reveal the transmission direction. The second algorithm applies scan likelihood ratio statistics followed by AGC index to visualize the dynamic changes of the local aggregation pattern of disease clusters at the regional level. Compared to the one-stage aggregation approach, Knox-based and AGC mapping were more sensitive in small-scale spatio-temporal clustering.
Highlights
The development of visual tools for the timely identification of spatio-temporal clusters will assist in implementing control measures to prevent further damage
The first two-stage algorithm performs the Knox test followed by the standard deviational ellipse (SDE) m ethod[12–15] and the second algorithm applies scan likelihood ratio statistics followed by AGC index to visualize the dynamic changes of the local aggregation pattern of disease clusters at the regional level
The total poultry farm census data was obtained by spatially merging the official poultry farm registration database (OPFRD) managed by the Council of Agriculture (COA), with an island-wide domestic waterfowl farms survey conducted by the Taiwan Agriculture Research Institute (TARI) utilizing remote satellite imaging technology between August 2016 and April 2017
Summary
The development of visual tools for the timely identification of spatio-temporal clusters will assist in implementing control measures to prevent further damage. The first two-stage algorithm performs the Knox test followed by the standard deviational ellipse (SDE) m ethod[12–15] and the second algorithm applies scan likelihood ratio statistics followed by AGC index to visualize the dynamic changes of the local aggregation pattern of disease clusters at the regional level. Both SDE and AGC maps along a regular time interval provide the visual ways of indicating the direction of virus transmission
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