Professor Philip Nolan:

Yes. Some early serology work suggested there might be several others, but the later work and careful detective epidemiological work suggests that is the ratio. As for county variation, and in fact international variations, it is very difficult to dissect out why one county is hit more than another. If the outbreaks and clusters of cases are taken out, one still sees county-by-county variation. We need to remember that Cavan and Monaghan are very close to Dublin by European standards, so it is not anomalous for the disease to be seeded in the capital, which is also the transportation hub, and then to spread out somewhat randomly in different directions from the capital.