http://www.nationalmssociety.org/Research-2001Oct2.asp

October 2, 2001

Summary:

Investigators have reported two apparent multiple sclerosis “clusters” (numbers of MS cases exceeding what would be expected) occurring within the populations of DePue, Illinois and El Paso, Texas.

Both studies occurred at sites near former metal smelters known to have contaminated the air and soil in their communities.

These studies present interesting data on MS clusters, but it is not possible to conclude with certainty that metals exposure, or any other factor, led to these clusters.

Individuals with concerns or questions about a possible MS cluster in their communities should contact the local (town, city, or state) public health department. The health department may refer such cases to the federal Centers for Disease Control’s ATSDR. ATSDR may be reached directly at 1-888-422-8737, e-mail ATSDRIC@cdc.gov, or by visiting its website at http://www.atsdr.cdc.gov/ .

Details: Investigators have reported two apparent multiple sclerosis “clusters” (numbers of MS cases exceeding what would be expected) occurring within the populations of DePue, Illinois and El Paso, Texas. Although the investigators note that the towns’ inhabitants were subjected to significant metals exposure for several decades, no definite conclusions are reached regarding the causative factors leading to these apparent MS clusters.

Background:

A cluster of MS can be defined as an unexpectedly high number of cases of MS that have occurred over a specific time period within a certain geographic area. To know if a cluster exists, epidemiologists must calculate the number of cases of MS that would be expected to occur in a given area over a given period of time, based on the total population at risk in the area. The expected number can then be compared with the reported number. Such clusters of MS – or of other diseases where clusters are reported – are studied to look for common causes or “triggering” factors that might explain them.

Multiple sclerosis is believed to occur in persons who have a genetically determined predisposition for the disease. But a great deal of evidence suggests that even people who are genetically susceptible must encounter some other factor or factors in their environment – infectious, environmental, or dietary, for example – in order for MS to develop. No such factor has been shown to be causally linked to MS and exactly what factor (or factors) may be involved remains an open question. So far, cluster studies have not produced clear evidence for the existence of any causative or triggering factor in MS. Two MS clusters have been recently reported and are described below.

Depue, Illinois:

In the mid-1990s, residents and former residents expressed concern for what appeared to be an unusually high number of cases of MS. At the request of the Illinois Department of Public Health, Dr. Randolph B. Schiffer (Texas Tech University Health Sciences Center, Lubbock) and colleagues undertook an investigation of this possible MS cluster, and the results are published in the September/October issue of Archives of Environmental Health.

The residents of this small town (population 1800) in north central Illinois had been exposed to trace metals in water and soil from a zinc smelter site that closed in the early 1980s. This former industrial site in DePue has been identified by state and federal health authorities as a potential public health concern and has been entered into the federal Superfund database of the Environmental Protection Agency.

In conjunction with the Illinois Department of Public Health, the investigators confirmed the diagnoses of nine people with MS, all of whom had developed symptoms between 1971-1990. Based on several different calculations of the expected rates of new cases of MS expected to occur over two decades in a town of this size, the investigators determined that the nine cases exceeded the expected cases (fewer than two).

The authors concluded that exposure to zinc or other trace metals could have been a factor in the occurrence of this MS cluster, although they have no direct evidence that zinc or any other metal is, in fact, related to MS. No other potential risk factors were measured, such as family relationships that might naturally elevate the individuals’ genetic predisposition for developing MS.

El Paso, Texas: In December 1994, a former El Paso, Texas resident with MS contacted the Texas Department of Health to report an apparent cluster of MS cases among people who spent their childhoods in the Kern Place/Mission Hills and Smeltertown areas of El Paso. Early in the investigation, concerns were raised about the possible impact of a local metal smelter, which was shown to have contaminated the air and soil with high levels of metals such as lead, arsenic, zinc, and cadmium.

The federal Agency for Toxic Substances and Disease Registry (ATSDR) of the Centers for Disease Control provided a grant to the Texas Department of Health to conduct a study among persons who had attended two elementary schools in the Kern Place/Mission Hills neighborhood and Smeltertown to determine the number of people who had been diagnosed with MS. Epidemiologist Judy P. Henry led the study, results of which were presented publicly on October 2, 2001 and may be published in the future.

Students who attended Mesita and E.B. Jones Elementary schools from 1948 through 1970 were eligible to be included in the study and were sent questionnaires asking for demographic and medical information. Dr. Randolph B. Schiffer reviewed the records of those who indicated they had MS to confirm the diagnosis.

The investigators identified and confirmed 14 cases of MS among former Mesita students. No cases were reported among former E.B. Jones students. The number of people with MS among former Mesita students is twice as high as expected, based on national estimates. This study was not designed to investigate the specific cause or causes of MS and the results cannot tell us why there is an excess of MS among the former Mesita students. Based on the findings, the investigators recommend further investigation of this cluster and possible factors that might be involved.

Conclusions:

Two reports of clusters of MS indicate higher-than-expected incidence of disease in two widely separate populations. No specific cause of the clusters has been identified. In both the DePue and El Paso studies, potential risk factors that might relate to MS were not taken into account in calculating the expected incidence of MS, and problems may exist in the reporting and population sampling in both clusters. These studies present interesting data on MS clusters, but it is not possible to conclude with certainty that metals exposure, or any other factor, led to these clusters.

Referral:

The major resource for individuals with concerns or questions about an MS cluster in their community is the local (town, city, or state) public health department. Public health officials are primed to hear about, and to investigate, suspected clusters. They may also refer such cases to the federal Centers for Disease Control’s ATSDR. Consumers may contact this agency directly by calling toll-free 1-888-422-8737, email ATSDRIC@cdc.gov, or by visiting its website at http://www.atsdr.cdc.gov/ .

From: Research Programs Department