Historical inquiry as a method of estimating the trend of leprosy

ABSTRACT

The records of Cordova and Talisay, Cebu, Philippine Islands, which have been the basis of several previous studies, have been utilized to illustrate the value of the historical method (as opposed to prolonged observation) in determining trend. A modified life table method of analysis was used. When the total experience of both communities was divided into years of life lived prior to and subsequent to January 1, 1915 and the study was limited also to the incidence of lepromatous leprosy only, it was found that there was evidence of a downward trend. The ratio of the incidence rate for the earlier to that for the later period was found to be, for males 1.3 to 1 and, for females, 2.0 to 1. Since in this comparison the later life experience of many persons exposed in the first period was included in the second, two groups of individuals were selected in such a manner that the life experiences of the groups were mutually exclusive. For the earlier period individuals born between 1896 and 1910 were selected and their life experience was included only to the year 1920. For the later period those born between 1911 and 1925 were chosen and their experience was included up to the year 1935. Thus, no individual in the first group was included in the second. Also all individuals, except those residing in the community less than ten years, had a minimum period of ten years of observation between entrance and termination of observation and none had more than twenty-five years of life experience. The downward trend of lepromatous leprosy was more strikingly evident in this second comparison than in the first. The ratio of the incidence rate for the earlier period to that for the later is for males, 2.0 to 1, and for females, 2.4 to 1. Evidently incidence had declined in the communities taken as a whole. The next question that arose was whether this downward trend could be detected in the experience of those who were known to have lived in the same household as a person with leprosy. Comparison was again made between the experience of those born between 1896 and 1910 and those born between 1911 and 1925. Only those who were known to have been living in household association with lepromatous leprosy were considered as exposed and their experience was contrasted with that of those for whom no history of exposure to any type of leprosy could be ascertained...