Background: After the Great East Japan Earthquake and Tsunami in March 2011, radioactive elements were released from the Fukushima Daiichi Nuclear Power Plant. Based on prior knowledge, concern emerged about whether an increased incidence of thyroid cancer among exposed residents would occur as a result.
Methods: After the release, Fukushima Prefecture performed ultrasound thyroid screening on all residents ages ≤18 years. The first round of screening included 298,577 examinees, and a second round began in April 2014. We analyzed the prefecture results from the first and second round up to December 31, 2014, in comparison with the Japanese annual incidence and the incidence within a reference area in Fukushima Prefecture.
Results: The highest incidence rate ratio, using a latency period of 4 years, was observed in the central middle district of the prefecture compared with the Japanese annual incidence (incidence rate ratio = 50; 95% confidence interval [CI] = 25, 90). The prevalence of thyroid cancer was 605 per million examinees (95% CI = 302, 1,082) and the prevalence odds ratio compared with the reference district in Fukushima Prefecture was 2.6 (95% CI = 0.99, 7.0). In the second screening round, even under the assumption that the rest of examinees were disease free, an incidence rate ratio of 12 has already been observed (95% CI = 5.1, 23).
Conclusions: An excess of thyroid cancer has been detected by ultrasound among children and adolescents in Fukushima Prefecture within 4 years of the release, and is unlikely to be explained by a screening surge.
From the aDepartment of Human Ecology, Graduate School of Environmental and Life Science, Okayama University, Okayama, Japan; bDepartment of Epidemiology, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama, Japan; and cDepartment of Information Science, Faculty of Informatics, Okayama University of Science, Okayama, Japan.
Editors’ Note: A commentary on this article appears on page 323.
Editors’ Note: Letters to the Editor regarding this article can be found on the EPIDEMIOLOGY website in the May 2016 issue at http://journals.lww.com/epidem/pages/default.aspx
Submitted 25 January 2015; accepted 10 August 2015.
Presented earlier aspects of this research at conferences of the International Society for Environmental Epidemiology in Basel (2013) and Seattle (2014).
The authors report no conflicts of interest.
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Correspondence: Toshihide Tsuda, Department of Human Ecology, Graduate School of Environmental and Life Science, Okayama University, 3-1-1 Tsushima-naka, Kita-ku, Okayama, 700-8530, Japan. E-mail: email@example.com.
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