Attack risk on infected properties during the 2007 equine influenza outbreak in New South Wales, Australia.

The research article focuses on calculating the risk of disease attack, specifically equine influenza, on infected properties and how those risks vary with the size of the property and its geographical location.

Objective and Methodology

• The researchers aimed to determine the proportion of seropositive horses on infected premises (IPs) in an attempt to understand the attack risk of equine influenza. Seropositive simply means horses that have developed antibodies against the virus, indicating past or current infections.
• To achieve this, they conducted logistic regression analyses. This is a statistical method that is used to examine the relationship between a binary outcome (in this case, whether equine influenza attacked or not) and one or more predictor variables (such as enterprise size and geographical location).

Findings

• The study found that the average attack risk during the outbreak was 96.88% (median 100%), meaning that almost all horses on infected premises were likely to contract the disease.
• However, it was found that the attack risk varied based on the size of the enterprise or farm, and specific geographical regions. This indicates that there were certain conditions or factors in those environments that influenced the spread of the disease.
• The highest attack risks were found in the Dubbo cluster/region while the Narrabri-Northern cluster showed the lowest risk. This could be due to various factors including different levels of exposure, variations in horse density, and potential regional differences in horse husbandry practices.
• In general, smaller properties with fewer horses tended to have higher attack risks than larger properties. It’s suggested that this is because larger properties may have better resources and practices in place to prevent the spread of infections. However, this was not consistent for all geographic clusters/regions revealing that regional factors also play a significant role in disease risk.