Factors influencing the proportion of non-examinees in the Fukushima Health Management Survey for childhood and adolescent thyroid cancer: Results from the baseline survey

BACKGROUND: After the Fukushima Daiichi Nuclear Power Plant accident, a preliminary ultrasound-based screening for thyroid cancer was conducted to establish a baseline for subsequent evaluations. In this survey, we assessed the relationship between the proportion of non-examinees and characteristics of the target populations. METHODS: After summarizing a regional difference of non-examinees among the population of 359,200 (primary evaluation) and 2,246 (confirmatory testing) individuals who were living in the Fukushima prefecture on 11 March 2011, we estimated odds ratios (ORs) for each characteristic including age, sex, area of residence, and moving after the accident, based on the proportion of non-examinees for the primary examination and the confirmatory testing, using a multivariate logistic regression model. RESULTS: The dataset included 64,117 non-examinees (primary evaluation) and 194 (confirmatory testing). The logistic regression result indicated that girls were not likely to be non-examinees compared to boys with adjusted OR of 0.80 (95% confidence interval[CI]:0.78-0.81) for the primary evaluation. OR was the lowest for children 6-10 years old (y/o) (OR=0.26, CI:0.25-0.27), and higher for those 11-15 y/o (OR=1.28, CI:1.25-1.32) and over 16 y/o (OR=5.30, CI:5.16-5.43) when compared to children 0-5 y/o. Individuals residing in the western part of the prefecture showed higher ORs. There was a higher proportion of non-examinees among those who moved after the accident compared to those who did not in the primary evaluation (OR=1.72, CI:1.64-1.79). CONCLUSIONS: In addition to the demographic characteristics, a change of residence could be a potential factor that influenced the proportion of non-examinees. Our results will help proper interpretation of reports and prospective management of the survey.