Identifying Disease Clusters – What Comes Next?

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It’s hard to say how many disease clusters have been identified. The website of the National Disease Cluster Alliance (NDCA) which held a national conference last week has a map that identifies 73 clusters. Several people attending the meeting pointed out that their cluster was not on the map and there are no doubt many others not on the map. While identifying clusters is an important step, knowing how to respond and what steps to take once a disease cluster (even a suspected disease cluster) has been identified is, perhaps, more important. This and other questions about disease clusters were discussed at a National Disease Cluster Conference held in Washington, DC last week by the NDCA.

It was clear from several presentations that no guidelines exist for what action steps a government agency should take once a disease cluster has been identified. This is a big problem, especially since most health agencies typically close their investigation once a cluster has been identified, concluding that they could not determine the cause of the cluster. This is not the time to walk away from a community that is struggling to determine not just whether a disease cluster exists, but what‘s causing it as well.

There are plenty of examples of communities where a disease cluster was identified. There is the cleft palate cluster in Dickson, TN, increase cancers in Clyde, OH, and childhood cancers in Toms River, NJ, Sierra Vista, AZ and Fallon, NV to name a few (see NDCA map). There are few examples, however, of agencies being able to identify the cause of the cluster. Woburn, MA is the exception as the state health department was able to identify contaminated drinking water wells as the cause of a childhood leukemia cluster.

No doubt determining the cause of a disease cluster is a difficult question to answer. It took the MA state health department over 10 years to conclude that the contaminated drinking water wells were the cause of the cluster in Woburn. But because it’s difficult is not reason enough for public health agencies to walk away. This is unconscionable and irresponsible. Public health agencies need to come up with an action plan for how to follow-up the finding of a cluster. Part of the response needs to include an environmental investigation into what may be causing the cluster. In addition, the community would likely benefit from the distribution of educational materials about the disease in question and the methods used to investigate clusters and their causes. Whatever follow-up occurs, the government needs to include from the very beginning of the process the affected community as part of the planning group directing the investigation.

One example highlighted at the conference was the work of Dr. Paul Sheppard from the University of Arizona who conducted an environmental investigation following the identification a childhood leukemia cluster in Fallon, NV. Between 1997 and 2004, 17 children living in Fallon were identified with leukemia, three of them died. For three years Sheppard studied heavy metals in air, especially tungsten which had been identified as increased in Fallon. Sheppard used tree leaves and tree rings to measure tungsten and found a high concentration of tungsten in the center of Fallon, the home to a tungsten refinery and a tungsten plant since the 1960s.

Although Sheppard was unable to prove that exposure to tungsten caused the increase in leukemia, his work has clearly related the two. His work provides a model for how to follow-up finding a disease cluster. Investigating environmental exposures in a community with a cluster makes perfect sense. Now we need to convince the public health agencies that they need to include this step in as part of their responsibilities. For more about the conference, see www.clusteralliance.org.

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By Leanna Theam. I grew up in the suburbs of sunny Southern California then moved to the opposite end of California to a small college