Overall frailty gauged in victims of the Italian plague (Imola, 1630-1632): was plague an indiscriminate killer?

Plague is an epidemic-prone infectious disease that has affected humanity with catastrophic effects throughout almost its entire history. One of the most intriguing questions of the last years is whether plague kills indiscriminately. To address the question regarding pre-existent health conditions, this study aims to assess the overall frailty of plague victims and compare it with a sample of non-plague victims from the same period and area. Frailty was assessed using the biological index of frailty (BIF) on two skeletal series dated to the seventeenth century from north-eastern Italy: one of plague victims from the Imola's Lazzaretto (n = 93) and another from an attritional cemetery located in Ravenna (n = 58). Comparisons between the BIF values of the two samples were performed separately by sex and age classes. Cox proportional hazards regression was conducted to analyze factors associated with the risk of dying from plague. The age-adjusted ANCOVA test revealed no significant differences in BIF results between the two samples. However, according to Cox's regression, individuals in the lowest BIF category (the least frail) had a significantly higher hazard of dying from plague. Although we found no differences between the mean frailty values of plague and non-plague victims in the univariate analysis, individuals with a low level of frailty showed a higher hazard of dying from plague than from other causes. In fact, otherwise healthier individuals (i.e., with low levels of frailty) could be found only among plague victims.