Reconstruction of diffusion at local scales: the 1846, 1882 and 1904 measles epidemics in northwest Iceland.

Because medical records of individuals contracting measles were not kept in northwest lceland for epidemics before 1904, the spread of the disease in 1846 and 1882 has been traced from notifications of death recorded in burial registers and census returns. Using this evidence, a time-space matrix of measles deaths has been constructed and the dynamics of the diffusion process through a necklace of small communities strung along the coast has been analysed. In each of the three epidemics the mortality curve corresponded closely to an S-shaped logistic model, each new epidemic passing through the area more rapidly than its predecessor. The operation of a neighbourhood effect from a single point of introduction implies that the disease should move in a wave-like form through the area. Whereas the 1882 epidemic advanced steadily as a wave-front progression characteristic of the neighbourhood effect, those of 1846 and 1904 had strong spatial biases towards the parish of Eyri. The intense localization of the outbreaks in 1846 and 1904 appears not to be related directly to distinctive features in the demography or form of the settlement. In 1904 a confirmation service held in Eyri church brought many victims into contact with a measles carrier, but no special circumstances have been reported or can be deduced for 1846.