The effect of leprotic infection on the risk of death in medieval rural Denmark

Introduction: Paleopathological studies of leprosy in Danish skeletal collections show that many individuals suffered from this stigmatized disease during the Middle Ages. This study examines the risk of death associated with leprotic infection in individuals from the Danish rural cemetery of Øm Kloster (AD 1172-1536). Specifically, we modeled the influence of leprotic infection on age-specific mortality accounting also for sex and social status (lay person / monastic).

Materials and methods: The sample consisted of 311 adult individuals from the Øm Kloster skeletal collection housed at the Institute of Forensic Medicine, University of Southern Denmark (ADBOU). We modeled morbidity and mortality using a three-state illness-death model with the following parameterizations for the three transition hazards: (1) nonlesioned to lesioned: constant; (2) nonlesioned to dead: Gompertz-Makeham; and (3) lesioned to dead: Gompertz-Makeham, directly proportional to the hazard of the well to dead transition.

Results: The mortality hazard of lesioned individuals exceeded that of nonlesioned individuals by a factor of 1.4 (40%) across all individuals, 1.7 for females, 1.0 for males, 1.3 for lay persons, and 1.7 for monastics. Overall, 15% of the sample died with skeletal manifestations of leprosy, though it is likely that a higher percentage of the population carried the bacterium.

Discussion: This study improves understanding of past health and population dynamics focusing on a chronic infectious disease. The methods employed could informatively be applied to larger analyses of community health from skeletal collections by incorporating more than one disease into the multistate model and inferring individual frailty using various skeletal markers.