Methods of Historical Epidemiology

Study of the epidemic briefly described by Thucydides has inspired discussions of how diseases in the distant past can be identified, and thus discussions of the methods of historical epidemiology. There are three difficulties that emerge in the literature of the Plague of Athens that can and have presented themselves in other retrospective diagnostic efforts. First has to do with "virgin soil" epidemics. Although Thucydides only implies that all members of society were at risk of contracting the sickness, that no one was immune, and that immunity was conferred on the survivors of infection, he does specifically state that the disease was previously unknown to lay and medical Athenians. Some scholars hold that a new disease among a population immunologically virgin to the microorganism in question need display neither the expected seasonal onset characterizing the disease nor the case-fatality rates usually seen. Those who oppose this methodological stance hold that this principle of retrospective analysis calls into question all diagnostic precepts. Many assume that supramortal-ity would cause a breakdown in normal nursing care and hygienic services, leading to excess mortality; therefore, they stress the need for distinguishing the socioeconomic effects of a virgin soil epidemic from discussions of the virulence of the disease or the immunologic vulnerability of the population.

The second difficulty pertains to the changing epidemiology (or even clinical presentation) of diseases over time and thus is a variation of what is called "virgin soil epidemics argument": that infections of the past may have been caused by an organism known today but that the organism behaved quite differently in past individuals and populations. As Littman and Littman (1969) observed, "[A]s diseases adapt to new hosts under changing environments over the passage of years the symptomatology may change." From a historical standpoint, this can be a particularly pessimistic argument, and, in fact, James Longrigg (1980) has disallowed the possibility of ever discovering the cause of the Plague on much these grounds: "Epidemic diseases inevitably become modified in the course of centuries of alternating widespread prevalence and quiescence and . . . symptoms can, in any case, vary considerably in accordance with diet." Poole and Holladay (1979) go even further in denying any possible resemblance of the Plague of Athens to an infectious disease known in more recent times, whereas Langmuir and colleagues (1985) suggest that the discussion abandon altogether the hope for a one-to-one correspondence with a modern infectious disease and look instead to a physiological understanding of the processes involved.

The third difficulty focuses on the intent and fidelity of Thucydides' account to actual events. Of the authors discussed in this essay, only Watson Williams (1957) argues that Thucydides himself might not have been terribly well informed about the epidemic, because he did not write his history until after 404 B.C., approximately 25 years after the epidemic had taken place. Williams further suggests that even if Thucydides wrote from notes or consulted one of the few physicians who survived (the account claims that most died early in the epidemic), individuals tended to believe that their own experience with an infection was characteristic of all those who suffered from it.

Most assume, however, that Thucydides' account of the events lacks some crucial details from a modern point of view, but is otherwise accurate. Since

Page's review, which offers abundant detail that Thu-cydides was particularly well versed in medical terms and ideas, most have come to believe that the account was informed by contemporary medical knowledge. Longrigg (1980) argees, but skeptically considers the possibility that Thucydides "dramatically exploited [the Plague] for historiographical purposes." On the other hand, Jody Rubin Pinault (1986), tracing an ancient legend that Hippocrates himself devised the successful remedy of building fires to combat the epidemic at Athens, argues that Thucydides' "silence about this remarkable achievement of Hippocrates" is compelling evidence that he was not at all well versed about the Plague.

Clearly, discussions of the causes of the Plague of Athens form an important and instructive example of the study of the history of human infectious diseases. In addition, such a study reveals the many pitfalls connected with this type of integration and points to the need for still more sophisticated methods and techniques.

Ann G. Carmichael

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