In Kettleman City, California, a town of 1,620 people, 11 babies were born with severe birth defects in the last three years. Meanwhile, at least 60 men who lived on the Camp Lejeune Marine Corps Base in North Carolina from the late 1950s into the 1980s have developed breast cancer. And residents in Wellington, Ohio are three times more likely to develop multiple sclerosis than in the rest of the country.

A new report highlights these and 39 other so-called 'disease clusters'—defined as unusual aggregations, real or perceived, of health events grouped together in time and space—that have been confirmed or are currently being identified by a local, state or federal agency in 13 US states since 1976. The 28 March report from two nonprofit organizations, the Natural Resources Defense Council (NRDC) and the National Disease Clusters Alliance, calls for expanded federal efforts to identify clusters and their causes.

“The report is pretty convincing,” says Melissa Bondy, director of the Childhood Cancer Epidemiology and Prevention Center, a joint endeavor of the Baylor College of Medicine and the MD Anderson Cancer Center in Houston. “There's a lot of perception that there's a problem with disease clusters, and I think that the only way we're going to know for sure is to investigate them properly.”

“Communities are worried about elevated disease rates,” adds Sarah Janssen, an NRDC senior scientist and a coauthor of the recent report. “There is a real need for thorough investigations in the communities where no one has come in to see whether or not a disease cluster exists.”

Pending legislation might help address the issue. A US Senate bill introduced in January called the Strengthening Protections for Children and Communities From Disease Clusters Act proposes to improve coordination between federal and state agencies and create guidelines for investigations. (The bill is also known as 'Trevor's Law', named for Trevor Schaefer, a brain cancer survivor who was diagnosed with the illness at the same time as others in his small Idaho community; an environmental cause was neither found nor ruled out.)

Ross Brownson, an epidemiologist at Washington University in St. Louis who previously oversaw cluster investigations at the Missouri Department of Health, says that more scrutiny of clusters is necessary: “It's good to bring attention to this issue and to think about it in a multifaceted way—to look at environmental issues, make use of the public health survey data we have and ensure that we're not investing all of our resources on a few clusters.”

Patricia Buffler, an epidemiologist at the University of California–Berkeley who has studied cancer clusters for three decades, praised the groups for calling for systematically reviewing clusters and federal funding. But she questions the report's conclusion that, as she puts it, “you see a cluster in a community, that there must be an environmental cause.” Although environmental contaminants were implicated in every documented cluster, only one mentioned in the report had a confirmed cause: asbestos contamination from a mine in Montana led to an outbreak of respiratory disease.