Sudden infant death syndrome, population mixing and oil-related development in western Norway

Abstract

ABSTRACTA number of features of sudden infant death syndrome (SIDS) point to an aetiological role for apparentlyminor infections. The spread of infections is influenced by the rate of contact between infectiouscases and susceptibles in the population. This is likely to differ geographically depending on patternsof social contacts, with epidemics being particularly likely where an influx of migrants leads to highrates of mixing of populations lacking herd immunity. It has been shown that geographical variationsin SIDS deaths in England and Wales are strongly associated with rates of long distance in-migrationinto districts. The large influx of population into parts of western Norway as a result of oil-related developmentprovides an opportunity to examine this issue further. The most intensive development hasbeen in the Stavanger area in the county of Rogaland. Published migration statistics show that therewas a rapid build-up of long distance migration into this area reaching a peak in the late 1970s. Furthernorth, the Bergen area in the county of Hordaland was little affected by oil-related activities in the1970s. However, the more recent development of oil provinces further north has led to more activity inthe Bergen area and an increase in in-migration from the mid 1980s onwards. Annual data from 1969onwards on SIDS deaths in Rogaland and Hordaland counties and for Norway were used to assesswhether trends in SIDS mortality and migration showed any associations. Before the main populationinflux Rogaland had a SIDS rate that was below the Norwegian average. However, since the mid1970s SIDS rates have been significantly in excess of the national average. In Hordaland SIDS rateswere low throughout the 1970s but increased substantially to be significantly in excess of the Norwegianaverage in the late 1980s. In both areas population influxes resulting from oil-related developmentwere therefore followed by a significant increase in mortality rates from SIDS. There is no evidencethat these trends can be accounted for by changing patterns of known risk factors for SIDS in theseareas nor of artefacts in the registration of SIDS cases. The results of this study therefore support theBritish evidence that population mixing may be a significant factor in the aetiology of SIDS.