DELAYED EFFECTS OCCURRING WITHIN THE FIRST DECADE AFTER EXPOSURE OF YOUNG INDIVIDUALS TO THE HIROSHIMA ATOMIC BOMB

¹ Laboratories of Atomic Bomb Casualty Commission, San Francisco, California

Thirty-three children who were exposed while in utero to the Hiroshima atomic bomb have head circumferences 2 or more standard deviations below normal. Twenty-four of these were between the seventh and fifteenth week of gestational age at the time of detonation of the bomb. The incidence and the severity of microcephaly increases as the distance from the hypocenter decreases. Mental retardation occurred in 15 of the 33 patients. The incidence of this defect was also related to distance from the hypocenter and gestational age. No other embryologic effects of exposure to the atomic bomb have been detected to date.

In 6 years ending in December, 1954, 19 persons who were within 2100 meters of the hypocenter have developed leukemia before attaining the age of 19 years. The annual incidence of this disease among those who were within 1500 meters and who were younger than 10 years of age at the time of exposure is 1:1000.

There are no cataracts that impair vision among the present pediatric group. An increased incidence of a mild visual disability, the cause of which is thus far indefinite, has been found among those now 16 through 19 years of age who were within 1800 meters of the bomb center. The incidence of chronic otitis media is the same for the 2 exposure groups, as are the means of the hematologic values for the patients with this ailment. There is no increase in the tumor incidence of the exposed children as compared with the nonexposed. There are no data to prove it, but the impression is that among the survivors the fear of late effects may be common and potentially disabling. Of those 19 years of age and younger, there were 2771 within 3000 meters of the hypocenter at the time of detonation of the bomb who were examined in 1954. Twenty-four of these had sequelae of the blast or thermal effects of the bomb other than well-healed scars. No other abnormalities related to atomic bomb exposure have been identified.

The review of the literature and the data presented in this report describe the late effects of exposure of young subjects to ionizing radiation or to nuclear weapons as known in the early part of 1955. The new information may be useful in the further definition of the tolerance of humans to ionizing radiation.

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