The model was constructed with binomial variance distributed according to a logistic function IPNV = [1 + exp[(-[beta])].
Seasonal data are also included because most IPNV cases occur in summer.
Mean IPNV prevalence was determined by region, and a [chi square] test of deviation from the overall Scottish mean was conducted (Table 1).
In marine sites, IPNV prevalence showed different temporal patterns in different regions (Figure 2).
In freshwater production sites, interannual variation in IPNV prevalence increased approximately 2% to 3% per year (Figure 3, Table 2).
The regions are becoming less distinct with respect to IPNV prevalence as the IPNV-positive regions converge.
Since slightly more sensitive methods were used to sample IPNV in freshwater than in saltwater, this difference may be underestimated.
Our analysis systematically shows that variation exists in the distribution of IPNV in Scotland and allows a detailed picture of changes in distribution to be derived.
The reasons for this are unclear, but the pattern suggests that controlling the emergence of IPNV may be possible.
The strength of this regional pattern is due to the extremely high prevalence of IPNV in Shetland and its low prevalence in the Outer Hebrides in both freshwater and saltwater sites.
As IPNV approaches ubiquity in Shetland, the virus has reached the saturation point; in many other areas, the increase remains rapid.
Our analysis is not intended to describe the absolute prevalence of IPNV in Scotland.