Where temperatures are already above the development threshold of 10°C the primary driver becomes changing rainfall patterns.
The first can be estimated by determining the date at which the base development threshold of 10.4°C mean daily air temperature is reached.
For the second measure, we determined the time period when insect larvae become abundant from accumulated temperature (degree days), i.e. the ambient temperatures exceed the base development threshold over a specific time.
To date there has been little increase in risk from overwintering larvae, as the minimum development threshold is still not consistently reached across a majority of the UK.
The single-sine method provides the most accurate degree-day quantification when daily temperatures are below the minimum development threshold (20 ), and has been used in other WNV studies to estimate risk (21 ).
Winters are predicted to become even milder and more months will have a mean temperature of above the 10°C development threshold.
The mean temperature was used as fasciolosis transmission can occur when night time temperatures are below the minimum development threshold of 10°C if they are compensated for by high day time temperatures [12].
The statistics used to define the threshold for WS outbreak provide a starting point for the development of thresholds for other diseases and/or locations, although data on the onset and development of a disease in each location would still be required.
In demonstrating the potential of this metric, we call for the continued collection of age-specific ILI data and additional research on the development of thresholds to define and differentiate mild from severe seasons.
