Paternal occupational contact level and childhood leukaemia in rural Scotland: a case–control study

Abstract

Significant increases of childhood leukaemia have repeatedly been recorded in situations of marked rural-urban population mixing, confirming the hypothesis that this disease has an underlying infective basis. For the increase in population density implicit in such mixing would increase the level of contacts between susceptible (more prevalent in rural areas) and infected individuals, thereby promoting an epidemic of the relevant infection. The infective agent in question is unknown, but the absence of marked space-time clustering of childhood leukaemia in the general population indicates that it must, as in known infection-based malignancies, be an uncommon response i.e. that the infection itself is largely immunizing. Adults as well as children appear to be involved in its transmission (Kinlen et al, 1993a;Kinlen, 1995).In the case of young (largely pre-school) children aged 0-4 years, an important contribution to their overall level of direct and indirect contacts will be made by fathers' contacts at work. 'High contact' occupations have already been associated with an increased incidence of childhood cytomegalovirus infection and paralytic poliomyelitis. Furthermore, in situations of extreme rural population mixing which had produced excesses of childhood leukaemia, risk was greater among the young children of those whose work involved many community contacts (Kinlen, 1997). No such increases have been found in mortality studies of the question in the (largely urban) general population of England and Wales (Kinlen, 1997;Fear et al, 1999). As an urban population would be expected to have the raised levels of immunity to infective agents often associated with high population density, we have considered the question still open as to whether high levels of paternal occupational contacts have effects on the incidence of childhood leukaemia in young children in a very rural area, where the prevalence of susceptible individuals would be unusually high.We have therefore investigated paternal occupational contact level in relation to childhood leukaemia in a national case-control study in Scotland in the period 1950-89, with particular reference to rural areas and the possible role of population mixing. METHODS Cases and controlsEligible cases consisted of children (aged 0-14) diagnosed in Scotland with leukaemia and non-Hodgkin's lymphoma (NHL) in the years 1950-89. For each child for whom a birth certificate was traced in Scotland that showed a parental occupation, 3 controls of the same age and sex were randomly chosen from the birth registers of the same county. A high proportion of the cases and controls had been included in an earlier investigation of paternal preconceptional occupational exposure to radiation (Kinlen et al, 1993b which gives further details of control selection). Young children (aged 0-4 years) were the main focus of our study, since in the case of older children, a change of paternal occupation is more likely between birth and diagnosis; nevertheless, older children were also investigated. So ...

A case–control study of childhood leukaemia and paternal occupational contact level in rural Sweden

“…The absence of paternal occupational effects in urban areas of Sweden accords with the findings in urban areas of Scotland (Kinlen and Bramald, 2001) and of England and Wales (Kinlen, 1995) and also in (the largely urban) England and Wales as a whole (Fear et al, 1999). This is also consistent with the findings of the many studies of population mixing situations.…”

“…In Sweden, children start primary school later than in many countries, at age 7 years, but earlier attendance in the smaller mixing units of kindergartens (from age 3 or 4 years) is common, though probably less so in rural areas. Against this background and the positive findings of two previous studies of rural Britain (Kinlen, 1997;Kinlen and Bramald, 2001), the results of the present study in Sweden are noteworthy: specifically, the significant relative excess of leukaemia in rural areas among the children aged 0 -4 years with fathers in high contact occupations, as well as the significant positive trend in these areas across categories of increasing contact level.…”

“…In the recent Scottish case -control study of childhood leukaemia and paternal contact level in rural areas (Kinlen and Bramald, 2001), a question left unresolved was whether the effect was typical of very rural areas (as much of Scotland is) or whether it was influenced by population mixing associated with the North Sea oil industry. The finding of a similar effect in the most rural group of Swedish counties without such population mixing suggests that it is not a prerequisite for observing these paternal occupational effects.…”

“…These were allocated as far as was possible to the contact categories used in our previous studies (Kinlen, 1997;Kinlen and Bramald, 2001) in which a much larger number of different occupational titles were available for allocation to the categories by six independent advisors. Two separate (but partly overlapping) classifications were applied, as in the earlier studies.…”

“…An examination of this question within the excesses of childhood leukaemia associated with extreme rural population mixing found a greater risk among the children of men in high contact jobs (Kinlen, 1997). Also, a recent case -control study found a significant positive trend in risk among pre-school children across three levels of increasing paternal occupational contacts in rural Scotland (Kinlen and Bramald, 2001) with each of the two classifications of contact level developed in the 1997 study.…”