Concerns continue over mercury and autism.

Stehr-Green et al. have misrepresented my work and confused the debate over autism and mercury exposure with ecologic data from Sweden and Denmark. Their report has many flaws. Four stand out. Their description of the California data promotes complacency regarding autism rates. For an Institute of Medicine (IOM) review, I presented an ecologic analysis of autism rates and mercury exposure demonstrating an association between rising autism rates in California and mercury exposure in childhood vaccines. In their re-use of my charts, the authors claimed incorrectly that the California data represented the larger class of “autism-like disorders.” California prevalence rates were reported based solely on autism cases. The authors’ suggestion minimized the severity of the California situation. These high and rising autism rates point to a public health emergency, and require accurate measurement and precise classification. Their autism cases account for a fraction of the autism population. The large majority of autism cases are found in outpatient populations. Yet, the analyses in Sweden (exclusively) and Denmark (for two thirds of the study period) rely on inpatient populations. One recent Danish study revealed that 93% of autistic records were for outpatients. Clearly, the small remaining group of inpatient registrations has little value in trend assessment. Their rate and exposure assessments contain multiple errors. These flaws are too numerous to mention here. (For a more detailed criticism of the Danish and Swedish analyses and a longer version of this letter, go to www.safeminds.org/.) Despite these flaws, they claim, inappropriately, that the choice of Swedish and Danish sources was based on “high quality records.” Their interpretation of the autism mercury hypothesis is incorrect. Based on these flawed trend assumptions, the authors use the shift in Sweden and Denmark to Thimerosal®-free vaccines in an attempt to falsify the autism–mercury hypothesis. Absent a clear increase in autism rates in Denmark and Sweden, this attempt fails. The autism-mercury hypothesis I tested was that increases in mercury exposure are associated with increases in autism rates. Reductions in comparatively low Thimerosal® exposures need not produce decreasing autism rates in stable, low-prevalence populations for the autism–mercury hypothesis to hold. Having performed the ecologic analysis with which the authors started, I fully recognize its failings. I do not wish to stand in defense of ecologic analysis. The authors’ attempts at trend analysis demonstrate the dangers of misusing ecologic analysis, especially when relying on shifting data sources and incomplete time series. Resources should flow instead to primary research. Credible evidence points to rapidly rising U.S. autism rates. Mercury exposure is temporally, epidemiologically, and clinically associable with U.S. autism cases and may help explain these increases. The IOM has called for an active research program that did not include ecologic speculations. Independent scientists should heed their recommendations, remain concerned over the autism-mercury connection and investigate further using proper methods.