IDSA 2011: Infectious Disease Epidemiology and Chronic Disease, Part I

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Julie Parsonnet, MD, argued that infectious disease plays a major role in causing chronic disease, but that links between them must be rigorously established.

BOSTON, MA—In a lecture to the annual meeting of the Infectious Diseases Society of America, Julie Parsonnet, MD, professor of medicine at the Stanford University School of Medicine, argued that the role of infectious disease as an underlying cause of chronic disease is much broader than generally recognized and that attaining a better understanding of the relationship between the two will require dogged epidemiological legwork.

For instance, Parsonnet pointed out that the Centers for Disease Control and Prevention listed microbial agents as the fourth leading cause of death in the US in 2000, but that it did not take into account the many instances in which microbial agents caused chronic disease such as hepatitis, cancer, and HIV, which in turn led to death.

In general, she suggested, there has been a lack of public understanding of the role of infection in causing chronic disease, in part because it is so difficult to do epidemiology of infection in chronic disease. Challenges include the difficulty of measuring exposure, the fact that critical exposure may occur long before a disease becomes apparent, and that chronic disease can come about through many different pathways. In addition, there is a temporal question: Which came first, exposure to the microbial agent or the disease?

Nonetheless, Parsonnet said, epidemiology of chronic disease caused by infection is better than that of chronic disease with other causes—and so far, the only Nobel prizes awarded relating to work on the pathogenesis of cancer have related to infectious diseases. One of these laureates, Johannes Fibiger, provides a cautionary tale: He studied rats in a Scandinavian sugar factory that had developed gastric cancer and found that all the cancerous rats had been colonized by a particular worm. Fibiger won the Nobel in 1926 based on his conclusion that the worms had caused the cancer, but as it turned out, the worms had not caused cancer in the rats; the rodents were sick because they ate only sugar and had a vitamin A deficiency. “This is the father of my field,” Parsonnet joked.

With the case of Fibiger in mind, Parsonnet urged the audience to be skeptical of purported links between infectious disease and cancer. As an example, she pointed to a New York Times article from last week on two independent research groups that found the same bacteria in colonic tumors. “There are a lot of us out there who think colon cancer is likely to be an infectious disease or partly an infectious disease,” said Parsonnet. “But unless you have epidemiology, these things are really hard to interpret. You have to keep that in the back of your mind that correlations do not necessarily mean causation.”

To read the second part of this article click here.

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