The elusive role of scientific medicine in mortality decline: diphtheria in nineteenth- and early twentieth-century Philadelphia.

The designation of the Klebs-Loeffler bacillus as the cause of diphtheria in the early 1890s and the subsequent development of the antitoxin treatment in the years immediately following were at the time and continue to be viewed as triumphs of scientific medicine. I focus on these two developments to illustrate the problems that arise in attempting to answer the questions regarding the role that changes in medical practice--in this case, the use of antitoxin as a cure--played in lowering death rates at the time. Changes in diagnostic techniques, the selection of cases to be included, and ultimately the agendas of the persons constructing them affected the numerators and denominators of these rates. The data suggest that the antitoxin had some effect on already declining diphtheria death rates, but because of changes in understandings of the disease and contemporaries' presentation of the data, the size of that effect and its role in mortality decline more generally elude us. Our analysis of the past depends on numbers that reflect not only changing treatments but also changing understandings of disease at the end of the nineteenth century.