Could these cases help researchers figure out what causes the disease?
SUMMARY: Multiple sclerosis clusters are puzzling events studied by researchers to better understand the disease. We profile 3 MS outbreaks in people exposed to zinc.
Even with the medical advances we enjoy in the 21st century, the cause of Multiple Sclerosis is still an unknown. MS occurs in people who have some kind of genetic predisposition for the illness, but research has shown that other – yet unknown – factors must be present for MS to develop.
Toxins, diet, infectious agents, and even climate have been suggested as triggering factors, but no definite cause has been identified yet.
In the quest to discover what causes MS, researchers have been puzzled by outbreaks of MS that occur in clusters, that is, a large number of cases occurring in a specific place over a specific period of time.
These clusters may provide clues about genetic risk factors or environmental causes that trigger the development of MS in susceptible individuals. So far, studying these cluster outbreaks have not offered clear answers, but remain an intriguing line of inquiry. Here, we present three verified cluster outbreaks that all occurred to people with greater-than-normal zinc and heavy metal exposures.
Identifying an MS cluster outbreaks
Before we discuss the outbreaks, we should first define the term cluster of MS and describe challenges involved in determining if a cluster exists.
A “cluster of MS” means that there is a greater number of MS cases in one area than would be normally be expected. Sometimes, what can appear to be an outbreak in a region is actually a statistically expected number of cases.
It can be difficult for researchers to determine if a cluster exists. The main reasons clusters are hard to identify are:
- Length of time between when disease starts and diagnosis
The beginning symptoms of MS can occur years before there is a definitive diagnosis. This means that someone can be diagnosed in one area when the clinical onset actually started somewhere else.
- MS can be difficult to diagnose
Many symptoms of MS can occur with other diseases; accurately diagnosis MS can be challenging.
- MS cases in an area occur by coincidence
People in one area can get MS unrelated to a common factor.
Three MS cluster outbreaks in people exposed to zinc and other metals
In all three of these cases of confirmed cluster outbreaks of MS, no specific causes were determined. Yet it an important data point for researchers that all of these outbreaks were in people exposed to higher-than-normal levels of zinc and other metals:
- El Paso, Texas
After reciving a tip from a former El Paso resident, investigators found with the Texas Department of Health confirmed 14 cases of MS among former students of Mesita Elementary School, which is located near a local smelter which contaminated both air and soil with metals such as arsenic, zinc, cadmium, and lead.
According to the National Multiple Sclerosis Society, “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.”
- DePue, Illinois
Here, the MS cluster occurred in an occupational setting. DePue residents had been exposed to trace metals in the soil and the water from a zinc smelter plant that had closed in the 1980s. Investigators with the Illinois Department of Public Health confirmed that the number of cases from 1971 to 1990 exceeded the expected number for a town of its size. The researchers suspect the zinc or trace metal exposure could have factored into the outbreak, but could not find direct evidence of these metals as the cause.
- Rochester, New York
Like the DePue and El Paso cases, this outbreak also has ties to zinc/metals exposures. Here, a cluster of 11 employees at a Rochester manufacturing plant were diagnosed with MS, having developed symptoms between 1971-79. The investigators could not find a difference in zinc exposure between workers who developed MS and those who did not, though predisposing genetic factors to the disease were not taken into account.
What should I do if I suspect an outbreak?
If you have concerns about MS in your community, your primary resource is your local public health department. Officials in these departments have the know-how to investigate suspected outbreaks.
Health departments that require additional investigation support may also contact the federal Agency for Toxic Substances and Disease Registry.
FROM THE HHN EDITORS: March is Multiple Sclerosis Education Month and we salute the people who study this puzzling disease. Cluster outbreaks such as the ones described in this article may provide useful clues for the environmental risks that might trigger the onset of MS.
Source: The National MS Society