Identifying signature features of epidemic diseases from 19th century all-cause mortality data.

Deadly epidemics leave distinct marks on all-cause mortality. When cause-specific health data are unavailable, studies of all-cause mortality may be necessary for understanding epidemic and pandemic diseases in history. Here, we identify and catalog every major epidemic in Denmark during the 100-year period between 1815 and 1915, based on a recently digitized and compiled data set of all 4 million burials during the period. Although the data set lacks specific information on cause of death, we were able to determine plausible etiology for the majority of 418 identified mortality crises that had more than 50 excess deaths. Epidemiologic methods, data analysis, consultation of historical sources, and investigation of the signature features of age patterns, seasonality, timing, and geography were used. The identified epidemics included, among others, pandemic influenza, cholera outbreaks in 1853 and 1857, and annually repeating epidemics during the period 1826-1832. Although these epidemics have been discussed elsewhere, our work presents a different view of these epidemics, based solely on all-cause mortality. Some of the identified epidemics were caused by pathogens that still affect us in modern times. In low-income modern settings for which representative population health data may be unavailable, the use of mortality data to determine the signature features may guide policy and improve future mitigation strategies.