The definition of an epidemic is simple, but subjective, warns Craig Newschaffer, professor and chairman of the department of epidemiology and biostatistics at the Drexel University School of Public Health: "An epidemic means that there are more cases of a disease than we would expect." He cites the example of smallpox, an affliction for which a single confirmed case would qualify as an epidemic, because the disease has been eliminated in humans. On the other hand, when everybody you know has a cold, that's to be expected, and therefore not an epidemic.
What about autism? In the last 20 years the number of reported cases has gone up—everyone agrees. But has autism increased more than expected? Are we in the midst of an autism epidemic?
It's hard to tell, for many reasons, and Newschaffer, to the dismay of many a reporter looking for a sound bite that answers the question, knows them all. ""For one thing," Newschaffer notes, "autism isn't one thing. It's a spectrum of disorders." That means different and perhaps unknown causes, risk factors, and genetic predispositions.
Might the increase in autism be due to improved diagnostics, that is, to children who would previously have been diagnosed with mental retardation or learning disabilities today being diagnosed with autism? Experts debate the issue. Parents worry that there's "something out there" causing autism.
"There are two major hypotheses," Newschaffer says. "One is that something is going on that increases children's risk of autism. The other is that the increased number of cases is due to changes in the autism diagnosis and an increased tendency to diagnose autism instead of something else."
What causes autism? "Like cancer, autism is a very complex disease," says Newschaffer, "and it's exciting to start asking questions about the interaction between genes and environment. There's really a very rich array of potential exposure variables."
Newschaffer says we don't know the cause of autism. That means autism diagnosis has to be made on the basis of behavior rather than biology—and that's the always unpredictable behavior of a child we're looking at. And studies that look back at the infant behavior of older children, before the disease was well-known, simply aren't a sharp enough tool to unearth, once and for all, whether autism was as common in the past as it is now.
There strong beliefs on both the "nature" and "nurture" sides of the issue," Newschaffer says. "But if you try to get objective and sit back –if you try to be honest –I don't think the data are valid, precise, or good enough to tease these things out." But "we need to consider environmental risk factors."
Many new studies are in progress. But Newschaffer doubts that a definitive answer will be found soon. "We are not likely to develop a conclusive body of evidence to either fully support or fully refute the notion that there has been some real increase in autism risk over the past two decades," he says.
In a 2005 study, Newschaffer and his colleagues concluded that shifting diagnostic categories alone can't account for the increase in autism cases. Newschaffer's data suggested some increase in autism cases. "Saying that it's an epidemic is a powerful word," he reminds us—it means more public attention and funding.
After the release of data from the Centers for Disease Control and Prevention (CDC) on autism prevalence in the spring of 2007, Newschaffer was invited to speak to the Congressional Caucus on Autism Research and Education to offer his expert opinion on the new data from the CDC autism and developmental disabilities monitoring (ADDM) project. The project indicates that almost seven in 1,000 8-year-old children had an autism spectrum disorder. The data, collected across multiple project sites nationwide, represents the best available estimate of the prevalence of autism in the United States. Fourteen ADDM project sites are established across the nation, including sites in Pennsylvania, New Jersey and Maryland. Newschaffer, who joined the faculty of the School of Public Health this past fall, was one of the first ADDM project principal investigators and remains affiliated with the Maryland ADDM project site.
Newschaffer stresses the importance of identifying common symptoms within the wide variety of autism spectrum disorders, as well as ways to better observe genes and the environment together. He also notes that several federally funded epidemiological studies are underway to pinpoint possible environmental triggers for autism, including an initiative by the CDC. Newschaffer serves as co-principal investigator of this CDC study, which is expected to review 2,700 children over the next five years.
He's working on an interesting new study, working at Drexel's 11th Street Clinic with mothers of autistic children—a "high-risk cohort—"who are now pregnant again. "The benefit of early identification is immeasurable," he says, although he does "hope to measure it." "We need to get the word out to families." He says that starting out at birth with a child at risk of autism offers the best hope that he might find the biomarkers for autism. "The richest samples" for biomarkers, he says, are in the placenta. "What genes are expressed by the baby in the womb?" he asks. The whole first year of the project, the year he's in now, calls for recruitment and outreach. "We're not rushing into data collection," he notes. "If you don't have a lot of data, you're not doing science."This is not treatment research."
The ultimate goal for Newschaffer and his colleagues is a comprehensive collection of all the available about the disease: the National Database for Autism Research NDAR (http://ndar.nih.gov/ ) "Adding to some body of knowledge: that's the goal. We're in public health," Newschaffer says, "to prevent mobility and mortality from diseases. A "cure" is really tertiary prevention—in public health we're really into primary prevention: stopping disease before it happens."
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Professor and chairman of the department of epidemiology and biostatistics at the Drexel University School of Public Health, Newschaffer was recently at the department of epidemiology at the Johns Hopkins Bloomberg School of Public Health. At Johns Hopkins, Newschaffer founded and directed the Center for Autism and Developmental Disabilities Epidemiology, one of five federally funded centers of excellence in autism epidemiology. Major initiatives included the development of methods for monitoring autism spectrum disorders prevalence and participation in the largest population-based epidemiologic study of autism risk factors to date – the National CADDRE Study of Autism and Child Development. Dr. Newschaffer also is engaged in other projects focusing on how particular genes might interact with environment exposures to increase autism risk. His recently began a collaboration with Peking University to explore approaches for conducting epidemiologic research on autism in China. Newschaffer is an Associate Editor of the American Journal of Epidemiology, and a member of the editorial board of the journal, Developmental Epidemiology.
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