Epidemiological approach to the paleopathological diagnosis of leprosy

In paleopathology it is usually assumed that modern diagnostic criteria can be applied to infectious diseases in the past. However; as both the human species and populations of pathogenic microorganisms undergo evolutionary c hanges, this assumption is not always well-founded. To get valid estimates of the frequency (the point prevalence at death) of leprosy in skeletal sam ples, sensitivity, specificity, and sample frequency must be estimated simu ltaneously. It is shown that more than three symptoms must be evaluated in at least three samples in order to reach estimates with well-described prop erties. The method is applied to three skeletal samples from Medieval Denma rk; the samples were scored for the presence of seven osteological conditio ns indicating leprosy. For the osteological conditions, sensitivity varied from 0.36-0.80, and specificity from 0.58-0.98. The frequency of leprosy in the three samples was: Odense (a lepers' institution), 0.98, 95% CI 0.64-1 .00; Malmo (urban cemetery), 0.02, 95% CI 0.00-0.07; and Tirup (rural cemet ery), 0.36, 95% CI 0.23-0.46. It is concluded that it is indeed possible to estimate disease frequencies without reference to modern standards, and th at leprosy occurred with widely differing frequencies in different segments of the Medieval population in southern Scandinavia. (C) 2001 Wiley-Liss, I nc.