Heath Responds to "Do Leukemia/Lymphoma Clusters Have an Infectious Cause?"

Clark W. Heath, Jr.

From 674 Plantation Point Road, Woodbine, GA

Reprint requests to Dr. Clark W. Heath, Jr., 674 Plantation Point Road, Woodbine, GA 31569-2124 (e-mail: cwheath{at}tds.net).

Received for publication August 1, 2005. Accepted for publication August 9, 2005.

As Dr. Law notes in his commentary (1Go), the evaluation of time-space clusters of childhood leukemia and lymphoma in residential communities is difficult. Since they often give rise to intense local concern, each cluster report deserves prompt public health attention. It is likely, however, that most clusters are the result of random time-place case distributions, despite statistical evidence showing some degree of nonrandom occurrence (2Go, 3Go). It is therefore not surprising that local investigations do not often yield information pointing to particular biologic causes.

When the Centers for Disease Control and Prevention (CDC) began its investigations of leukemia clusters 40 years ago, the focus was principally on infectious causation. Leukemogenic viruses had been discovered in different animal species, and there was strong interest in extending the search to humans. That interest was heightened when one of the earliest CDC investigations suggested a relation of case occurrence to local school and parish affiliations (4Go). Of the many investigations that followed, however, only on a few occasions were features found that appeared to link cases beyond their time-place closeness. Observations in each instance (described in my article (5Go)) suggested infectious causation.

Field investigations were undertaken only if the incidence of childhood leukemia was clearly increased in the communities under question. The task then was to collect personal information about the family and community activities of affected children, as well as information on community characteristics, that might suggest patterns of shared risk. Beyond the initial focus on infection, the CDC investigations gave considerable attention to other possible risk factors, and on several occasions surveys were conducted to measure community levels of exposure to chemicals and radiation. While failure to identify such environmental risks by no means rules out their potential role, neither do circumstances compatible with the spread of infectious agents necessarily establish infectious causation.

At the start of the CDC investigations, it was hoped that laboratory studies might become available to help in the search for causal factors, especially for infectious agents. In anticipation of such work, serum and peripheral blood specimens were obtained in some investigations from patients and their families and in the course of community surveys. Lacking laboratory help, however, investigations eventually depended entirely on descriptive epidemiology.

The particular association of increased incidence of childhood leukemia and lymphoma with newly formed communities, both in the CDC investigations and in later British studies (6Go), adds epidemiologic support to the idea of infectious causation. Further studies of case occurrence in such community settings in particular may be useful in the future, but perhaps only if such research can be coupled with laboratory approaches arising from our increasing understanding of how infection, immune susceptibility, and genetic makeup may underlie the etiology of such illnesses.


    ACKNOWLEDGMENTS
 
Conflict of interest: none declared.


    References
 TOP
 References
 

  1. Law GR. Invited commentary: do clusters of leukemia and lymphoma provide evidence for an infectious cause? Am J Epidemiol 2005;162:823–4.[Free Full Text]
  2. Knox G. Epidemiology of childhood leukaemia in Northumberland and Durham. Br J Prev Soc Med 1964;18:17–24.[ISI][Medline]
  3. Alexander FE, Boyle P, Carli P-M, et al. Spatial temporal patterns in childhood leukaemia: further evidence for an infectious origin. Br J Cancer 1998;77:812–17.[ISI][Medline]
  4. Heath CW Jr, Hasterlik RJ. Leukemia among children in a suburban community. Am J Med 1963;34:796–812.[CrossRef][ISI]
  5. Heath CW Jr. Community clusters of childhood leukemia and lymphoma: evidence of infection? Am J Epidemiol 2005;162:817–22.[Abstract/Free Full Text]
  6. Kinlen L. Evidence for an infective cause of childhood leukaemia: comparison of a Scottish New Town with nuclear reprocessing sites in Britain. Lancet 1988;2:1323–7.[CrossRef][ISI][Medline]




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