The Geography of Illness
DISEASE MAPS: Epidemics on the Ground. Tom Koch. xii + 330 pp. University of Chicago Press, 2011. $45.
What should we expect maps of disease actually to do? asks medical geographer Tom Koch in Disease Maps, a chronological and sometimes philosophical review of the practice of that field. Disease mapping is no mere mill of induction in which epidemiological truths leap from the engraver’s table, he insists. Nor is it simply another way of representing data. Rather, Koch wants us to see maps as arguments: They embody an “if-then” structure, with the simplest “if” being the trustworthiness of information about the existence of the disease and its accurate location. But a general concept of experimental design might better represent Koch’s point, for the mapmaker selects variables pertaining not only to characteristics of disease but also to elements of place and matters of scale. At issue is not merely the reliability of input, but the choosing of variables and their reciprocal relation to the questions the map answers.
The book opens with a discussion of theory mapping and its contemporary practice, using a routine mapping of an outbreak of severe diarrhea in Vancouver as demonstrative exemplar. Koch then turns to the past, beginning with the 16th-century anatomist Andreas Vesalius, whom Koch depicts as having initiated naturalistic visual representation in medicine. A discussion of early modern plague epidemics includes the celebrated bills of mortality of John Graunt, raising issues of where mappable information should come from. Then, following a chapter on yellow fever, are six chapters on cholera, which make up roughly half the book. Three of these, and parts of two others, focus on England in the era of John Snow, discoverer of the water- borne character of cholera and key recognizer of fecal-oral disease transmission. It is with Snow’s legacy as medical mapmaker that Koch wants mainly to engage. He compares Snow’s approach with the proto-epidemiology of others who studied the same outbreaks in roughly the same places—William Farr, John Simon, Henry Whitehead and, in lesser degree, John Sutherland and Henry W. Acland—and reviews Edmund Alexander Parkes’s criticisms of Snow’s reasoning. In the last of these chapters, Koch traces the emergence of the cult of Snow among early 20th-century American promoters of a science-based public health, and suggests too how a modern disease-mapper would approach the Soho cholera outbreak, which led to Snow’s famous map of cases clustered around the Broad Street Pump. The final chapters, focusing on the 20th century, illustrate the use of mapping techniques on a variety of scales for other diseases, particularly typhoid and polio, and, all too briefly, the emergence of cancer mapping from the late 19th century to contemporary cancer registries.
As a critical medical cartographer, Koch is insightful. He helps us see more clearly what Snow did and didn’t do—how Henry Whitehead’s work went well beyond Snow’s, and how Farr, and particularly the misunderstood Simon, conceived the problem significantly differently. The treatment of Snow is perhaps belabored, certainly out of balance with the coverage of any other individual or episode, and yet the chapters are a needed antidote to the misleading—indeed, irresponsible—popularizations of Snow in recent years, and move some way toward a less Snow-centric approach to the conceptual history of epidemiology. Additionally, I found the chapter on cancer mapping fascinating. It covers too much too quickly, but it reveals nicely the extraordinary range of cartographic possibility.
The rest of the book is weak, however, reflecting insufficient engagement with relevant areas of scholarship in social history and the history of medicine and science, and in historical geography and the epidemiology-related aspects of the philosophy of the social sciences. As a result, the reader frequently gets the sense in earlier chapters of being presented with one (beautiful) map after another. There are no clear criteria for their selection; the theoretical or political circumstances of each are not fully developed; and there is little sense of changing concepts and institutions.
Medical mapping began to flourish in the 19th century. A fuller consideration of how the practice fit in the emergent epidemiology of that era is needed. At first glance, its primacy may seem obvious. A map lets us “see” how at least some kinds of disease work. Pioneering statists of the period (predecessors of our statisticians) were no less interested than we are today in “seeing” determinants of incidence and prevention, but for them space did not stand above other variables that might be juxtaposed with proxies of health status, such as mortality rates or incidence of discrete pathological states (calling them “diseases” in our sense can risk anachronism). All these approaches involved a common mode of reasoning (Koch’s “argument”), but much more than diagnostic and cartographic accuracy were at issue. The privileging of space (equally the joining of space with time, a variant underdeveloped here) involved not merely a means of testing theories about disease but a reconceptualization of disease itself as essentially and not merely incidentally spatial. That concern is marked in the ultimate ascendency of a concept of “contagious” or “infectious” diseases, terms with changing meanings across the 19th century.
Approaching these matters merely in terms of mapping, rather than from the perspective of the history of statistics and epidemiology or that of clinical medicine and theories of pathology, invites a misrepresentation of context and of concepts. Exemplifying the latter is a common error, the conflating of a wide range of atmospheric variables with a so-called miasmatic theory of disease. Among these atmospheric variables were Thomas Sydenham’s “epidemic constitutions,” which might overlap with geophysically caused atmospheric states, as well as asphyxiating atmospheres, toxic gases or suspensions, marsh effluvia (closest to the usual technical definition of “miasm”), and various types of human or animal effluvia. The properties of some of these agents overlapped with those of the presumed contagia of specific diseases; they have a variety of implications for the generality or specificity of pathological processes (Koch’s misrepresentation of Sydenham’s concept of disease is particularly problematic) and suggest different ways for thinking about the distribution of disease in space (and time). Further conflation of “miasma” with anticontagionism exacerbates these problems. The fine discussion of the cholera assessments of Snow, Farr and company would be much richer conceived in terms of changing conceptions of diseases (which are more fundamental than different causal hypotheses).
Fuller attention to social, institutional and political settings too would be needed to make sense of how disease mapping develops. Implicit in Koch’s treatment is the idea of a common trajectory: Later medical mappers build on the work of earlier ones. Their repertoire broadens, but it appears to be, at least potentially, a universal one. This is made possible by common approaches to defining diseases, training epidemiologists, gathering statistics and making maps. Yet that universality did not automatically happen; much more attention, particularly to colonial and tropical disease-mapping and to the coming of international public-health institutions, would be needed for readers to get a sense of how the map-making tool meshed with other modes of representation and inquiry.
The book’s strengths, as well as its weaknesses, reflect general features of the easy interdisciplinarity of contemporary scholarship. Fascinating texts from other times and places are now marvelously accessible to all. That accessibility can (and should) enrich many forms of contemporary inquiry, but it often does so at the cost of sophisticated interpretation. By contrast, earlier generations of scholars would have met such texts, if at all, only within well-developed bibliographic-interpretive traditions embodied in disciplinary communities. Failure to engage with the scholarship is this book’s greatest weakness. Many seminal works (and authors) are missing from Koch’s bibliography; frequently the sources used are not the authoritative works on their subjects. The consequence is that a beautifully produced book, with lovely typography and fascinating maps, is much less substantive than it should be, and ultimately a disappointment. I can recommend only chapters 8 through 11, on Snow-related issues. Although these need to be read in conjunction with other work on mid-19th-century epidemiology, they well represent Koch’s own considerable expertise and acuity.
Christopher Hamlin is professor of history at the University of Notre Dame, and honorary professor at the London School of Hygiene and Tropical Medicine. He specializes in the history of public health and is most recently the author of Cholera: The Biography (Oxford University Press, 2009).