Airborne infectious diseases during infancy and mortality in later life in southern Sweden, 1766–1894

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Abstract
Background The importance of early life conditions and current conditions for mortality in later life was assessed using historical data from four rural parishes in southern Sweden. Both demographic and economic data are valid. Methods Longitudinal demographic and socioeconomic data for individuals and household socioeconomic data from parish registers were combined with local area data on food costs and disease load using a Cox regression framework to analyse the 55–80 year age group mortality (number of deaths = 1398). Results In a previous paper, the disease load experienced during the birth year, measured as the infant mortality rate, was strongly associated with old-age mortality, particularly the outcome of airborne infectious diseases. In the present paper, this impact persisted after controlling for variations in food prices during pregnancy and the birth year, and the disease load on mothers during pregnancy. The impact on mortality in later life stems from both the short-term cycles and the long-term decline in infant mortality. An asymmetrical effect and strong threshold effects were found for the cycles. Years with very high infant mortality, dominated by smallpox and whooping cough, had a strong impact, while modest changes had almost no impact at all. The effects of the disease load during the year of birth were particularly strong for children born during the winter and summer. Children severely exposed to airborne infectious diseases during their birth year had a much higher risk of dying of airborne infectious diseases in their old age. Conclusions This study suggests that exposure to airborne infectious diseases during the first year of life increases mortality at ages 55–80.