HIGH-CONTACT PATERNAL OCCUPATIONS, INFECTION AND CHILDHOOD LEUKEMIA -5 STUDIES OF UNUSUAL POPULATION-MIXING OF ADULTS

The hypothesis has been tested that, among excesses of childhood leuka emia associated with extreme population-mixing the incidence is higher for the children of men in occupations involving contact with many in dividuals (particularly children), as noted in certain childhood infec tions. Data on childhood leukaemia were examined from five previous st udies of the author in which significant excesses had been found assoc iated with population-mixing involving adults. Occupational titles wer e categorized according to the estimated level of work contacts as med ium, high, Very high or indeterminate. Occupations involving frequent contact with children were categorized as having a very high contact l evel given the high frequency of exposure to the infection postulated as underlying childhood leukaemia. There was a significant positive tr end (P < 0.001) in childhood leukaemia risk at ages 0-14 years across the occupational contact categories from the reference group (comprisi ng the medium and low plus indeterminate categories) through high to v ery high (i.e. high-child) contact categories in the combined data fro m the author's five studies of adult population-mixing; this significa nt trend also applied at ages 0-4 (P < 0.001) and 5-14 (P < 0.01) year s. The excess in the high category was mainly because of paternal occu pations connected with the construction industry and transport, sugges ting a broader definition of the 'very high' contact category. No sign of these excesses was found in a limited examination of the question outside areas of population-mixing using mortality data for childhood leukaemia in the general population of England and Wales. The findings represent the first individual-based support for infection underlying childhood leukaemia that is promoted by population-mixing, as well as further support for the role of adults in transmission of the infecti on.