ee eT ek 76 OF Cet BRAT A ADAMSET AL. TABLEII Age Distribution of Hepatitis B Seronegative Persons in Rongelap Exposed and Comparison Groups Percentage seronegative Group Number of Numberof Meanage(+SD) Age group persons seronegative seronegative (years): 29-39 40-49 >49 61 Lt 39.7 + 10.8 25.0(7/28) 16.7(2/12) 9.5 (2/21) 95 9 41.7+ 10.3 12.2 (5/41) 10.0(2/20) 5.9 (2/34) >0.30 >0.50 >0.30 tested Rongelap exposed Rongelap comparison persons persons P value* * x? analysis of Rongelap exposed versus comparison group. Antibody to 6 antigen was determined by a blocking enzyme immunoassay using human anti-é IgG and é antigen derived from chimpanzee liver. Statistical testing ofdifferences in the prevalence of HB markers was performedby x? analysis ofindependence between two or more groups; the Kruskal-Wallis test was used for comparing HBsAgratio units. Analysis by age was based on the groupings of <29, 29-39, 40-49, and >49 years. Since the adult prevalence ofpositive hepatitis B serology was reached during the second decadeorearlier,it was judged probable that most persons >49 years of age had acquired hepatitis B prior to the 1954 fallout, whereas the younger groups would include those most likely to express an interaction between radiation exposure and acquisition of the infection. RESULTS Serologic evidence of prior hepatitis B infection was widespread by adulthood in the Marshallese population tested (Table I), with the sexes showing equivalent preva- lences. No significant difference in the prevalence of at least one hepatitis B marker was detected when evaluated accordingtoatoll of residence (x (3) = 1.86, P > 0.50), age group (x? (3) = 1.10, P > 0.70), or radiation exposure group (x? (2) = 4.36, P > 0.10). The prevalence of seronegativity did not differ significantly between the Rongelap exposed and the comparison group (x? (1) = 1.88, P > 0.10), even when analyzed by age (TableII). HBsAgwas detected in 1 1.5% ofthe total population tested (Table I). The relatively low prevalance in the exposed Rongelap population was notsignificantly different from the comparison group (x? (1) = 1.83, P > 0.10). All of the Utirik population tested were exposed, thereby precluding a comparison of their very high prevalence with unexposed Utirik inhabitants. Because the prevalence of HBsAg by atoll was also lowest on Rongelap (x? (3) = 19.39, P< 0.001), prevalence byatoll was recalcul- ated after excluding the exposed Rongelap group.A statistically significant variation amongatolls remained apparent(x? (3) = 14.18, P< 0.01), with Rongelapstill having the lowest prevalence. When grouped by age, the oldest population had the highest mrmas rms CSi P39 # csi prevalence of HBsAg (Table I), although group differences were notstatistically significant (x? (3) = 1.77, P > 0.50). The meanlevels of HBsAg antigen (+SD) among