Population density and childhood leukaemia: results of the EUROCLUS Study

Associations Between Built Environment Characteristics and Walking in Older Adults in a High-Density City: A Study From a Chinese Megacity

The built environment is an important factor affecting physical activity, especially walkability. Walkability is used to characterize the user friendliness of outdoor physical activity. However, studies on walkability and physical activity are mainly concentrated on low-density Western cities. Study on the walkability of high-density cities in Asia, especially with the elderly, is seriously lacking. And walkability is often used as a composite indicator. This study mainly re-examines the relationship between the common indicators of walkability (population density, street connectivity, land-use mix, and retail density), transport-related walking, and leisure-time walking with older adults in China's megacities. Twelve housing estates in Wuhan were selected for study areas. We explored the association between the walking activities of 1,161 elderly people (≥60 years old) and the indicators of walkability in their neighborhoods. Socio-demographic characteristics were controlled in the multilevel logistic regression models of the built environment walking associations. We found that there was no significant correlation between the four indicators of walkability and transport-related walking. Street connectivity is significantly positively correlated with the participants' leisure-time walking (OR = 1.499, 95% CI = 1.068~2.103), and there was no significant correlation between the other indicator of walkability and leisure-time walking. The results show that there was no statistical correlation between walkability and transport-related walking in the elderly, and only one indicator was related to leisure-time walking. It is extremely important to re-examine the characteristics of built environments and elderly walking activities in high-density cities. Only by implementing effective intervention strategies in different urban backgrounds can cities move toward a more active and healthier path.

Relation between residential density and walking time among urban adults in Nanjing, China

OBJECTIVES

The interest in built environment attributes on physical activity has been rapidly increasing over recent decades. This study aimed to investigate the associations between residential density (RD) and walking time (WT), a common mode of physical activity, among urban adults in China.

STUDY DESIGN

This is a cross-sectional study.

METHODS

Locally registered adults aged 35-74 years were randomly selected from eight urban neighbourhoods in Nanjing, China, in 2017. The outcome variable was self-reported WT (dichotomised), whereas RD (in tertiles) was the independent variable. Mixed-effects regression models were introduced to examine the RD-WT association via computing odds ratios (ORs) and 95% confidence intervals (CIs).

RESULTS

Of 1568 eligible participants, 98.9% completed the survey, with a mean age (standard deviation) of 54.7 (11.1) years, in which 46% were men. After adjustment for potential confounders, a negative gradient RD-WT association was seen across RD tertiles among the participants (OR = 2.88 [95% CI = 1.79, 4.64] and 2.10 [95% CI = 1.35, 3.26] for lower and middle tertiles, respectively, compared with the upper RD tertile). The negative RD-WT association was observed for both men and women.

CONCLUSIONS

RD was negatively associated with the WT of urban adults in China. These results have public health implications for improving community-level physical activity through development of walking-friendly built environment.

The association between residential density and physical activity among urban adults in regional China

BACKGROUND

Studies from Western countries reported a positive relationship between residential density (RD) and physical activity (PA) among adults. There was no such study from China, a rapidly-urbanizing country in the world. This study aimed to investigate the RD-PA association among urban adults in China.

METHODS

A multistage sampling approach was used to randomly select participants (aged 35-74 years old) in urban areas of Nanjing in 2017. The outcome variable was PA (dichotomized into "sufficient" or "insufficient"), while the independent variable was RD (tertiled into three sub-groups). Odds ratios (OR) and 95% confidence interval (CI) were computed to examine the RD-PA association using mixed-effects logistic regression models with adjustment for age, sex, nationality, marriage, educational attainment, employment status, body weight status, green space and neighborhood-level clustering effects.

RESULTS

Of the 1568 eligible participants, 1551 were interviewed (response rate = 98.9%), with the mean age (standard deviation) of 54.7 (11.1) years old, and 46% of men. After adjustment for potential confounders and community-level clustering effects, participants lived in communities with higher (OR = 0.31, 95% CI = 0.21, 0.47) and middle (OR = 0.70, 95% CI = 0.50, 0.99) residential density were significantly less likely to achieve sufficient physical activity relative to their counterparts lived in the lower densed communities. Similar negative RD-PA association was examined for men or women, separately. The difference in the ORs between the middle and higher RD tertiles was also statistically significant (P < 0.01).

CONCLUSIONS

A negatively gradient RD-PA association, independent of body weight status and green space, was observed among urban adults in regional China. It has public health implications for China to help residents' promote and maintain physical activity through planning and constructing PA-/health-friendly built environment in future.

Residential density was negatively associated with excess body weight among adults in an urban region of China

BACKGROUND

Residential density was found to be associated with excess body weight among adults in Western societies but it remains unclear in China. We aimed to explore the relationship between residential density and excess body weight among adults in China.

METHODS

This cross-sectional study was conducted in 2017 in urban areas of Nanjing, China. A multi-stage sampling method was used to randomly select participants aged 35-74 years from 8 urban neighborhoods in Nanjing. Status of excess body weight was the outcome variable which was categorized as "yes (BMI≥24)" or "no (BMI<24)" according to specific recommendations for Chinese adults. Residential density was the main explanatory variable which was grouped into tertiles. Odds ratios (OR) and 95% confidence interval (CIs) were calculated to assess the relationship between residential density and excess body weight using mixed-effects regression models after adjusting for age, sex, education, occupation, marital status, redmeat, smoking, physical activity, diabetic status and potential neighborhood-level clustering effect.

RESULTS

A total of 1551 participants were recruited with a response rate of 98.9% (1551/1568). The mean age (standard deviation) of participants was 54.7 (11.1) years, and 46% of them were men. With adjustment for potential influential factors, participants in neighborhoods with lower (OR = 1.38, 95% CI = 1.06-1.81) and middle (OR = 1. 29, 95% CI = 1. 01, 1. 64) tertile of residential density were at significantly higher risk of gaining excess body weight relative to their counterparts in communities with upper tertile of residential density. Such a negative association between residential density and excess body weight was observed for men only after stratified analysis by gender.

CONCLUSIONS

A negative association between residential density and excess body weight was identified in overall and male urban Chinese adults, and the association was independent of physical activity. Results of our study have important implications in guiding public health policy making regarding prevention of excess body weight at community level via establishment of health-friendly neighborhood environment in China.

Green Neighborhoods, Food Retail and Childhood Overweight: Differences by Population Density

Purpose.

This study examines relationships between overweight in children and two environmental factors—amount of vegetation surrounding a child's place of residence and proximity of the child's residence to various types of food retail locations. We hypothesize that living in greener neighborhoods, farther from fast food restaurants, and closer to supermarkets would be associated with lower risk of overweight.

Design.

Cross-sectional study.

Setting.

Network of primary care pediatric clinics in Marion County, Indiana.

Subjects.

We acquired data for 7334 subjects, ages 3 to 18 years, presenting for routine well-child care.

Measures.

Neighborhood vegetation and proximity to food retail were calculated using geographic information systems for each subject using circular and network buffers. Child weight status was defined using body mass index percentiles.

Analysis.

We used cumulative logit models to examine associations between an index of overweight, neighborhood vegetation, and food retail environment.

Results.

After controlling for individual socio-demographics and neighborhood socioeconomic status, measures of vegetation and food retail significantly predicted overweight in children. Increased neighborhood vegetation was associated with decreased risk for overweight, but only for subjects residing in higher population density regions. Increased distance between a subject's residence and the nearest large brand name supermarkets was associated with increased risk of overweight, but only for subjects residing in lower population density regions.

Conclusions.

This research suggests that aspects of the built environment are determinants of child weight status, ostensibly by influencing physical activity and dietary behaviors.

Spatial analysis of childhood cancer: a case/control study

Background

Childhood cancer was the leading cause of death among children aged 1-14 years for 2012 in Spain. Leukemia has the highest incidence, followed by tumors of the central nervous system (CNS) and lymphomas (Hodgkin lymphoma, HL, and Non-Hodgkin’s lymphoma, NHL). Spatial distribution of childhood cancer cases has been under concern with the aim of identifying potential risk factors.

Objective

The two objectives are to study overall spatial clustering and cluster detection of cases of the three main childhood cancer causes, looking to increase etiological knowledge.

Methods

We ran a case-control study. The cases were children aged 0 to 14 diagnosed with leukemia, lymphomas (HL and NHL) or CNS neoplasm in five Spanish regions for the period 1996-2011. As a control group, we used a sample from the Birth Registry matching every case by year of birth, autonomous region of residence and sex with six controls. We geocoded and validated the address of the cases and controls. For our two objectives we used two different methodologies. For the first, for overall spatial clustering detection, we used the differences of K functions from the spatial point patterns perspective proposed by Diggle and Chetwynd and the second, for cluster detection, we used the spatial scan statistic proposed by Kulldorff with a level for statistical significance of 0.05.

Results

We had 1062 cases of leukemia, 714 cases of CNS, 92 of HL and 246 of NHL. Accordingly we had 6 times the number of controls, 6372 controls for leukemia, 4284 controls for CNS, 552 controls for HL and 1476 controls for NHL. We found variations in the estimated empirical D(s) for the different regions and cancers, including some overall spatial clustering for specific regions and distances. We did not find statistically significant clusters.

Conclusions

The variations in the estimated empirical D(s) for the different regions and cancers could be partially explained by the differences in the spatial distribution of the population; however, according to the literature, we cannot discard environmental hazards or infections agents in the etiology of these cancers.

Association between perceived urban built environment attributes and leisure-time physical activity among adults in Hangzhou, China

BACKGROUND

Neighborhood built environment may influence residents' physical activity, which in turn, affects their health. This study aimed to determine the associations between perceived built environment and leisure-time physical activity in Hangzhou, China.

METHODS

1440 participants aged 25-59 were randomly selected from 30 neighborhoods in three types of administrative planning units in Hangzhou. International Physical Activity Questionnaire long form and NEWS-A were used to obtain individual-level data. The China Urban Built Environment Scan Tool was used to objectively assess the neighborhood-level built environment. Multi-level regression was used to explore the relationship between perceived built environment variables and leisure-time physical activities. Data was collected in Hangzhou from June to December in 2012, and was analyzed in May 2013.

RESULTS

Significant difference between neighborhood random variations in physical activity was identified (P=0.0134); neighborhood-level differences accounted for 3.0% of the variability in leisure-time physical activity. Male residents who perceived higher scores on access to physical activity destinations reported more involvement in leisure-time physical activity. Higher scores on perception of esthetic quality, and lower on residential density were associated with more time in leisure-time walking in women.

CONCLUSIONS

The present study demonstrated that perceived urban built environment attributes significantly correlate with leisure-time physical activity in Hangzhou, China.

Associations of residential density with adolescents' physical activity in a rapidly urbanizing area of Mainland China

In the context of recent social and economic transitions in China, lack of physical activity among adolescents is an emerging health risk, particularly so in rapidly expanding urban areas. Evidence from Western countries suggests that built environment attributes can influence the physical activity participation of young people, but whether or not this is the case for China is unknown. We recruited high school students from ten urban districts in Nanjing, Mainland China (n = 2,375; mean age = 13.9 +/- 1.0 years old; 46% boys; survey response rate = 89%). The outcome variable was self-reported recreational physical activity time; the primary explanatory variable was the residential density of the urban districts. Analysis was conducted using mixed-effects logistic regression models. After adjustment for potential confounding variables, including sedentary behavior and green space, there was a consistent and graduated association between residential density and physical activity; residential density was significantly negatively associated with recreational physical activity time for students from the higher tertile of residential density (OR; 95% CI = 0.64; 0.42 to 0.97) compared to those from the lower tertile. The direction and magnitude of the negative association between residential density and physical activity was similar for boys and girls. It should be a public health priority to identify the particular urban environment attributes that can encourage and support young people's participation in physical activity.

Environmental factors and childhood acute leukemias and lymphomas

This review considers recent studies regarding the role of environmental factors in the etiology of childhood leukemia and lymphoma. Potential environmental risk factors identified for childhood leukemia include exposure to magnetic fields of more than 0.4 micro Tessla, exposure to pesticides, solvents, benzene and other hydrocarbons, maternal alcohol consumption (but only for certain genotypes), contaminated drinking water, infections, and high birth weight. The finding of space-time clustering and seasonal variation also supports a role for infections. There is little evidence linking childhood leukemia with lifetime exposure to ionizing radiation although fetal exposures to X-rays are associated with increased risk. Breast-feeding, consumption of fresh fruit and vegetables and having allergies all appear to be protective. Burkitt lymphoma (BL) is confined to areas of the world where malaria is endemic, with the additional involvement of the Epstein-Barr virus (EBV) as a co-factor. Environmental risk factors suggested for other types of non-Hodgkin lymphoma (NHL) include exposure to ionizing radiation (both lifetime and antenatal), pesticides, and, in utero exposure to cigarette smoke, benzene and nitrogen dioxide (via the mother). Hodgkin lymphoma (HL) is especially associated with higher levels of socioeconomic deprivation, but breast-feeding seems to confer lower risk. This is consistent with an infection or immune-response mediated etiology for HL.

Spatial clustering of childhood cancer in Great Britain during the period 1969-1993

The aetiology of childhood cancer is poorly understood. Both genetic and environmental factors are likely to be involved. The presence of spatial clustering is indicative of a very localized environmental component to aetiology. Spatial clustering is present when there are a small number of areas with greatly increased incidence or a large number of areas with moderately increased incidence. To determine whether localized environmental factors may play a part in childhood cancer aetiology, we analyzed for spatial clustering using a large set of national population-based data from Great Britain diagnosed 1969-1993. The Potthoff-Whittinghill method was used to test for extra-Poisson variation (EPV). Thirty-two thousand three hundred and twenty-three cases were allocated to 10,444 wards using diagnosis addresses. Analyses showed statistically significant evidence of clustering for acute lymphoblastic leukaemia (ALL) over the whole age range (estimate of EPV = 0.05, p = 0.002) and for ages 1-4 years (estimate of EPV = 0.03, p = 0.015). Soft-tissue sarcoma (estimate of EPV = 0.03, p = 0.04) and Wilms tumours (estimate of EPV = 0.04, p = 0.007) also showed significant clustering. Clustering tended to persist across different time periods for cases of ALL (estimate of between-time period EPV = 0.04, p =0.003). In conclusion, we observed low level spatial clustering that is attributable to a limited number of cases. This suggests that environmental factors, which in some locations display localized clustering, may be important aetiological agents in these diseases. For ALL and soft tissue sarcoma, but not Wilms tumour, common infectious agents may be likely candidates.

Specific viruses were not detected in Guthrie cards from children who later developed leukemia

There are hypotheses concerning infectious mechanism in the development of acute lymphoblastic leukemia (ALL). The first genetic event often happens in utero, based on studies from Guthrie cards. The authors have summarized the results from their studies concerning infectious mechanism. Presence of human polyomaviruses, parvovirus, HHV-6, EBV, and CMV were investigated by PCR from Guthrie cards from children who later developed ALL and healthy controls. Neither of these viruses were detected from patients nor from controls. The results do not support that these viruses have contributed to the development of a substantial part of the ALL cases in Swedish children.

Infectious etiologies of childhood leukemia: plausibility and challenges to proof

Infections as well as environmental exposures are proposed determinants of childhood acute lymphoblastic leukemia (ALL), particularly common precursor B-cell ALL (cALL). Lines of investigation test hypotheses that cALL is a rarer result of common infection, that it results from uncommon infection, or that it ensues from abnormal immune development; perhaps it requires a preceding prenatal or early childhood insult. Ideally, studies should document that particular infections precede leukemiA and induce malignant transformation. However, limited detection studies have not directly linked specific human or nonhuman infectious agents with ALL or cALL. Primarily based on surrogate markers of infectious exposure, indirect evidence from ecologic and epidemiologic studies varies widely, but some suggest that infancy or early childhood infectious exposures might protect against childhood ALL or cALL. Several others suggest that maternal infection during pregnancy might increase risk or that certain breast-feeding practices decrease risk. To date, evidence cannot confirm or refute whether at least one infection induces or is a major co-factor for developing ALL or cALL, or perhaps actually protects against disease. Differences in methodology and populations studied may explain some inconsistencies. Other challenges to proof include the likely time lag between infection and diagnosis, the ubiquity of many infections, the influence of age at infection, and the limitations in laboratory assays; small numbers of cases, inaccurate background leukemia rates, and difficulty tracking mobile populations further affect duster investigations. Nevertheless, existing evidence partially supports plausibility and warrants further investigation into potential infectious determinants of ALL and cALL, particularly in the context of multifactorial or complex systems.

Methods for detecting disease clustering, with consideration of childhood leukaemia

In trying to interpret reports of disease clusters in specific localities, it is valuable to know whether the disease in question has a general tendency to cluster spatially. Methods for investigating localized disease clustering were the subject of a comparative study organized by the International Agency for Research on Cancer some years ago. This paper addresses some further aspects of one of the methods used in this exercise, namely the Potthoff-Whittinghill (P-W) test. Particular consideration is given to methodology for estimating the magnitude of overdispersion and for detecting whether one area, in particular, has an undue influence on the evidence for overdispersion using the P-W test, the extent to which is possible to detect clustering over regions of differing sizes using a components-of-variance approach and how adjustment for overdispersion might affect tests for raised disease rates in specific locations. These points are illustrated using data on childhood leukaemia incidence and reference is made to other analyses of the geographical distribution of childhood leukaemia that are based on this approach.

Spatial and space-time clustering of childhood acute leukaemia in France from 1990 to 2000: a nationwide study

This study aimed to investigate the spatial and space–time distributions of cases of childhood acute leukaemia (CL) during 1990–2000 over the whole French territory. A global spatial heterogeneity and a spatial autocorrelation were first considered using the methods proposed by Potthoff and Whittinghill, Moran and Rogerson methods. The presence of space–time interaction between the places of residence and the dates of diagnosis was investigated with the Knox's test. Finally, the Kulldorff's statistic permitted to scan the whole territory in search for localised clusters. Two time periods were considered (1990–1994, 1995–2000). Overall, a statistically significant spatial heterogeneity of a very small magnitude was observed in the incidence of CL over 1990–1994, but neither over 1995–2000 nor over the whole time period. Moreover, a significant overdispersion of 5.5% was evidenced for 0–4 year children living in isolated areas with more than 50 inhabitants per km². Cases older than 10 years living in the same area at diagnosis also tended to cluster within 6 months.

Occurrences of Leukemia Subtypes by Socioeconomic and Occupational Groups in Sweden

OBJECTIVE

The objective of this study was to examine the associations between socioeconomic/occupational factors and histologic subtypes of leukemia.

METHODS

The Swedish Family-Cancer Database was used to calculate standardized incidence ratios for different social classes and occupational groups.

RESULTS

The overall standardized incidence ratio was close to unity between different socioeconomic groups, except for female manual workers with a significantly decreased risk. Among male occupations, increased risks were noted for sales agents, seamen, and chemical process workers. For female occupations, increased risks were observed among mechanics, iron and metalware workers, hairdressers, and launderers and dry cleaners.

CONCLUSIONS

The present study suggests that socioeconomic/occupational factors have a minor effect on the risk of leukemia. Occupational groups with possible exposure to organic solvents and other chemicals such as chemical process workers, mechanics, iron and metalware workers, and launderers and dry cleaners may entail true risk for leukemia.

Detecting small-area similarities in the epidemiology of childhood acute lymphoblastic leukemia and diabetes mellitus, type 1: a Bayesian approach

Childhood acute lymphoblastic leukemia and diabetes mellitus, type 1, have common epidemiologic and etiologic features, including correlated international incidence and associations with infections. The authors examined whether the diseases' similar large-scale distributions are reflected in small geographic areas while also examining the influence of sociodemographic characteristics. Details of 299 children (0-14 years) with acute lymphoblastic leukemia and 1,551 children with diabetes diagnosed between 1986 and 1998 were extracted from two registers in Yorkshire, United Kingdom. Standardized incidence ratios across 532 electoral wards were compared using Poisson regression, confirming significant associations between population mixing and the geographic heterogeneity of both conditions. Bayesian methods analysis of spatial correlation between diseases by modeling a bivariate outcome based on their standardized incidence ratios was applied; spatial and heterogeneity components were included within a hierarchical random effects model. A positive correlation between diseases of 0.33 (95% credible interval: -0.20, 0.74) was observed, and this was reduced after control for population mixing (r = 0.18), population density (r = 0.14), and deprivation (r = 0.06). The Bayesian approach showed a modest but nonsignificant joint spatial correlation between diseases, only partially suggesting that the risk of both was associated within some electoral wards. With Bayesian methodology, population mixing remained significantly associated with both diseases. The links between diabetes and acute lymphoblastic leukemia observed for large regions are weaker for small areas. More powerful replications are needed for confirmation of these findings.

An infectious aetiology for childhood acute leukaemia: a review of the evidence

There are three current hypotheses concerning infectious mechanisms in the aetiology of childhood leukaemia: exposure in utero or around the time of birth, delayed exposure beyond the first year of life to common infections and unusual population mixing. No specific virus has been definitively linked with childhood leukaemia and there is no evidence to date of viral genomic inclusions within leukaemic cells. The case-control and cohort studies have revealed equivocal results. Maternal infection during pregnancy has been linked with increased risk whilst breast feeding and day care attendance in the first year of life appear to be protective. There is inconclusive evidence from studies on early childhood infectious exposures, vaccination and social mixing. Some supportive evidence for an infectious aetiology is provided by the findings of space-time clustering and seasonal variation. Spatial clustering suggests that higher incidence is confined to specific areas with increased levels of population mixing, particularly in previously isolated populations. Ecological studies have also shown excess incidence with higher population mixing. The marked childhood peak in resource-rich countries and an increased incidence of the childhood peak in acute lymphoblastic leukaemia (ALL) (occurring at ages 2-6 years predominantly with precursor B-cell ALL) is supportive of the concept that reduced early infection may play a role. Genetically determined individual response to infection may be critical in the proliferation of preleukaemic clones as evidenced by the human leucocyte antigen class II polymorphic variant association with precursor B-cell and T-cell ALL.

Infections and immune factors in cancer: the role of epidemiology

An infective, mostly viral, basis has been found in an increasing number of different human cancers. In all cases, the neoplasm is a rare response to the relevant infection, which is usually present in persistent form, and requiring specific cofactors for malignancy to develop. In some cases, epidemiological evidence of infectivity preceded and promoted identification of the specific infection involved and even the discovery of the microbe itself, as in Burkitt's lymphoma and cervix cancer. In other cases, the discovery of the agent came first as in stomach and nasopharynx cancers, and epidemiology has been concerned mainly with confirming the relationship, measuring the size of the risk and identifying cofactors. Infection-linked cancers include some of the commonest malignancies in certain large world regions, amounting to over 20% of all cancer in the developing countries. In addition to these cancers are others such as childhood leukaemia that show features indicative of an infective basis though no underlying agent has been identified. Advances in this field invite speculation about possible future discoveries and how these might be promoted. However, in that majority of cancers that are unrelated to sexual behaviour, there will be nothing even at the population level to suggest an infective basis because what is transmitted from one individual to another is not the neoplasm itself, but the underlying, often silent, infection to which the malignancy is an uncommon response. The increasing prevalence of immune impairment in human populations, as a result of the use of immunosuppressive drugs with organ transplants and the spread of HIV infection, has produced marked effects on cancer incidence in the affected groups including increases, of skin cancers, non-Hodgkin's lymphoma and Kaposi's sarcoma and to a lesser extent of many other cancers, in some cases at least due to the release from immunological control of incipient infection-based malignancies.

Childhood leukaemia incidence and the population mixing hypothesis in US SEER data

We evaluated the infectious aetiology hypothesis of childhood leukaemia that rapid population influx into rural areas is associated with increased risk. Using data from the US SEER program, we found that in changes in rural county population sizes from 1980 to 1989 were associated with incidence rates for childhood acute lymphocytic leukaemia (ALL). The observed associations were strongest among children 0-4 years of age, born in the same state as diagnosis, in extremely rural counties, and when counties adjacent to nonrural counties were excluded. Similar analyses for brain and central nervous system (CNS) cancer in children, a disease less linked to this infectious hypothesis, provide evidence against methodologic bias. Similar evaluations for other decades were not meaningful due to limited sample sizes and, perhaps, increased population mobility.

Environmental exposure to PCBs and cancer incidence in eastern Slovakia

In a population-based cross-sectional study, we compared serum levels of 15 polychlorinated biphenyl (PCB) congeners and three organochlorine pesticides in residents of two districts in eastern Slovakia, one with extensive environmental contamination from a former PCB production site (Michalovce) and the other matched on geography but with low (background) levels (Svidnik). The age-adjusted geometric means for sum of 15 measured PCB congeners were statistically significantly higher in subjects from the Michalovce district for both sexes: 3327.6 versus 1331.4 ng/g of lipid in males, 2751.8 versus 992.2 ng/g of lipid in females. Levels of DDE and DDT were also significantly higher, although the absolute differences were less pronounced. There was no substantial difference in HCB levels between the districts. We also conducted an ecologic study to compare cancer incidence occurring in these same two districts from 1985 through 1994. We calculated standardized incidence ratios (SIRs) and 95% confidence intervals for each district using indirect standardization and rates from eastern Slovakia. Among males from Michalovce (exposed), but not Svidnik (unexposed), there was an excess of cancer of the tongue (SIR=1.46; 1.06-1.96), stomach (SIR=1.15; 1.00-1.32), lung (SIR=1.14; 1.04-1.24), testis (SIR=1.40; 0.97-1.97), and kidney (SIR=1.23; 0.98-1.52), and lower than expected incidence of prostate cancer (SIR=0.83; 0.69-0.97); in contrast, there was an excess of peritoneal (SIR=3.05; 1.11-6.63) and laryngeal cancer (SIR=1.43; 0.99-1.98) in Svidnik not observed Michalovce. Among females from Michalovce, but not Svidnik, there was an excess of cancer of the lip (SIR=2.54; 1.53-3.96), stomach (SIR=1.22; 1.02-1.44), and lung (SIR=1.17; 0.94-1.45); in contrast, there was an excess of kidney (SIR=1.61; 1.03-2.40) and thyroid (SIR=1.97; 1.12-3.20) cancer in Svidnik not observed in Michalovce. Taken together, these results raise the possibility that high environmental exposure to organochlorines in the Michalovce district may be associated with higher rates of certain cancers, particularly stomach and lung cancer.

Geographical and ecological analyses of childhood acute leukaemias and lymphomas in north-west England

Childhood leukaemias and lymphomas have been associated with exposure to environmental factors, including infections, which show geographical variation. This study examined the geographical distribution of the incidence of acute leukaemia and lymphoma using Manchester Children's Tumour Registry (MCTR) data 1976-2000. A total of 910 children were included, all of whom had histologically and/or cytologically verified leukaemia or lymphoma. At the time of their diagnoses, all the children were aged 0-14 years and were resident in the counties of Greater Manchester or Lancashire. Standardized morbidity ratios were calculated. Poisson regression was used to examine the relationship between incidence rates and small-area (census ward) population density, ethnic composition and deprivation index. There was a monotonic relationship between acute lymphoblastic leukaemia (ALL) incidence and population density (P = 0.05). Higher rates were seen in more densely populated areas. There was evidence for a monotonic relationship between the incidence of the mixed cellularity subtype of Hodgkin's disease (HD) and the Townsend deprivation score (P = 0.001). Markedly higher incidence was associated with greater levels of unemployment and household overcrowding. The results for ALL and mixed cellularity HD support the involvement of environmental factors, such as infections, in disease aetiology.

Increased frequency of mannose-binding lectin insufficiency among children with acute lymphoblastic leukemia

Epidemiological data indicate that acute lymphoblastic leukemia (ALL) could be induced by interactions between the immune system and early childhood infections. Mannose-binding lectin (MBL) plays a critical role in the immune response in early childhood before specific immune protection develops. We investigated whether there may be an association between childhood ALL and low-producing MBL genotypes. Serum MBL levels depend on normal (A) or defective (O) alleles, and on normal (Y) or reduced (X) promoter activities. For this study, 137 noninfants with ALL and 250 controls were classified into 3 MBL genotype groups according to their influence on the serum level of functional MBL: group I, YA/YA and YA/XA (higher levels); group II, XA/XA and YA/O (intermediate levels); and group III, MBL insufficiency with XA/O or O/O (MBL-deficient) genotypes. Compared with controls, cases more often had low-level genotypes (I/II/III: 63 [46%]/44 [32%]/30 [22%] vs 145 [58%]/65 [26%]/40 [16%]; P =.02) and MBL deficiency (8.8% vs 2.8%; P =.009). Thus, the ALL odds ratio for MBL-deficient versus nondeficient individuals was 3.3 (95% CI, 1.3-8.7), whereas the ALL odds ratio for group I versus group II/III genotypes was 0.62 (95% CI, 0.41-0.94). MBL group III patients were significantly younger at diagnosis than patients in group I/II (median, 3.9 vs 5.2 years; P =.04). The study shows that the presence of low-level MBL genotypes is associated with an increased risk of childhood ALL, particularly with early age at onset.

Population mixing, childhood leukaemia, CNS tumours and other childhood cancers in Yorkshire

We tested the hypothesis that variation in population mixing attributable to the diversity of migrants moving to an area is associated with the incidence of childhood leukaemia and other childhood cancers. An ecological analysis was performed on 954 children (<15 years) diagnosed with a malignancy between 1986 and 1996 in 532 electoral wards in Yorkshire, UK. Incidence rate ratios (IRR) were calculated for all childhood leukaemias (n=325), acute lymphoblastic leukaemia (ALL) (n=248), central nervous system (CNS) tumours (n=236) and other solid tumours (n=393) Incidence of all childhood leukaemias was significantly lower in areas of high (top decile) population mixing (IRR 0.72, 95% Confidence Interval (CI) 0.54-0.97) and higher in areas of low (bottom decile) population mixing (IRR 1.56, 95% CI 0.73-3.34), but similar patterns of incidence were not observed for central nervous system or other solid tumours. Population mixing may be a proxy for the range of infections circulating in a community and these results are consistent with the hypothesis that greater exposure to infections reduces the risk of developing childhood leukaemia by conferring efficient modulation of the immune system.

Population mixing and leukaemia in young people around the La Hague nuclear waste reprocessing plant

In order to investigate for an association between population mixing and the occurrence of leukaemia in young people (less than 25 years), a geographical study was conducted, for the years 1979 to 1998, in Nord Cotentin (France). This area experienced between the years 1978 and 1992 a major influx of workers for the construction of a nuclear power station and a new nuclear waste reprocessing unit. A population mixing index was defined on the basis of the number of workers born outside the French department of 'La Manche' and living in each 'commune', the basic geographical unit under study. The analyses were done with indirect standardisation and Poisson regression model allowing or not for extra-Poisson variation. Urban 'communes' were considered as the reference population. The Incidence Rate Ratio was 2.7 in rural 'communes' belonging to the highest tertile of population mixing (95% Bayesian credible interval, 95%BCI=1.2-5.9). A positive trend was observed among rural strata with increasing population mixing index (IRR for trend=1.4, 95%BCI=1.1-1.8). The risk became stronger for Acute Lymphoblastic Leukaemia in children 1-6 years old in the highest tertile of population mixing (IRR=5.5, 95%BCI=1.4-23.3). These findings provide further support for a possible infective basis of childhood leukaemia.

Is the timing of exposure to infection a major determinant of acute lymphoblastic leukaemia in Hong Kong?

The hypothesis that protection of infants from exposure to infectious agents with delayed first exposure to one or more specific agents together contribute to the aetiology of childhood leukaemia, especially common acute lymphoblastic leukaemia (cALL), has substantial indirect support from descriptive epidemiology and case-control studies in developed Western countries. A case-control study of childhood leukaemia diagnosed at ages 2-14 years has now been conducted in Hong Kong. Cases (n=98) formed a consecutive series of Chinese children diagnosed with acute leukaemia; controls (n=228) were identified following a survey using random digit dialling and required to attend for medical examination by a paediatrician. Interviews with mothers were conducted in hospital by one trained interviewer using a structured questionnaire. Odds ratios (OR) and 95% confidence intervals (CI) are reported for exposure variables capable of serving as proxies for exposure to infection in two critical time periods: first year of life, year before reference date (diagnosis for cases, corresponding date for controls). Analyses used logistic regression with adjustment for appropriate confounders. Change of area of residence reduced risk if during the first time period (OR = 0.47 [95% CI 0.23, 0.98]) and increased risk if during the second (OR=3.92, [95% CI 1.47, 10.46]). Reported roseola and/or fever and rash in the first year of life reduced risk (OR=0.33 [95% CI 0.16, 0.68]) whereas tonsillitis in the period 3-12 months before reference date increased risk (OR=2.56 [95% CI 1.22, 5.38]). Some other proxies for exposure to infection at the critical times were associated with predicted patterns of risk but day-care attendance failed to show predicted associations. These results provide support for the delayed exposure hypothesis in an affluent geographical setting in which population exposure to infectious agents is quite distinct from the settings of previous case-control studies.

Leukemia in childhood and adolescence and exposure to ionizing radiation in homes built from uranium-containing alum shale concrete

Concerns in Sweden about indoor radon around 1980 prompted measurements of gamma-radiation from the facades of houses to identify those constructed of uranium-containing alum shale concrete, with potentially high radon concentrations. To evaluate any possible risk of acute lymphocytic leukemia from exposure to elevated gamma-radiation in these homes, we identified the acute lymphocytic leukemia cases less than 20 years of age in Sweden during 1980-1989 as well as eight controls per case from the population registry, matching on age, gender, and county. Using the existing measurements, exposure was assessable for 312 cases and 1,418 controls from 151 properly measured municipalities. A conditional logistic odds ratio of 1.4 (95% confidence interval = 1.0-1.9) was obtained for those ever having lived in alum shale concrete houses, with the average exposure exceeding 0.10 microsieverts per hour. Comparing those who ever lived in alum shale concrete houses (divided by higher and lower annual average exposure) with those who never lived in such houses, we found a weak dose-response relation. The results suggest some risk of acute lymphocytic leukemia from indoor ionizing radiation among children and young adults.

Space-time clustering of childhood lymphatic leukaemias and non-Hodgkin's lymphomas in Sweden

BACKGROUND

The discussion concerning clusters of childhood leukaemia has mainly been focused on their relation to the time and place of diagnosis. Recently some studies have indicated clustering not only at diagnosis, but also around time and place of birth. Space-time clustering at time of birth could be of special interest if the aetiological agent is of infectious origin and the induction of leukaemia either occurs pre- or perinatally or an infection at that time favours a poor subsequent immune response to the agent.

METHODS

To identify possible space-time clustering we have used the close-pair method of Knox. One-thousand-twenty recorded cases (0-14 years) of childhood acute lymphatic leukaemia and 293 cases (0-14 years) of malignant non-Hodgkin's lymphoma from Sweden between 1973-1996 were analysed. The records include date of birth and of diagnosis as well as addresses at birth and at diagnosis.

RESULTS

A significant excess of case-pairs (25 observed, 14.9 expected, p = 0.01) was observed close in date and place of birth in the 4-14 year age group with acute lymphatic leukaemia (ALL). However there was no statistically significant clustering found around time of diagnosis. When the cases of leukaemia and the non-Hodgkin's lymphomas were combined no statistically significant clustering was obtained neither at birth nor at diagnosis.

CONCLUSIONS

This study strengthens the evidence of space-time clustering around the birth date in children whom later developed ALL. This observation is in support of the hypothesis that pre- or perinatal infections can induce a process leading to ALL.

Occupation and leukemia: a population-based case-control study in Iowa and Minnesota

BACKGROUND

Studies have suggested that risk of leukemia may be associated with occupational or industrial exposures and risk may vary by the histological type of the disease.

METHODS

A population-based case-control study was conducted in Iowa and Minnesota to evaluate the association between various occupations, industries, and occupational exposures and leukemia risk. A total of 513 cases and 1,087 controls was included in the study. A lifetime occupational history and other risk factor information were collected through in-person interviews, and a job-exposure matrix was used to assess possible risks associated with specific exposures.

RESULTS

A significantly increased risk of leukemia was observed among agricultural service industries and among nursing and healthcare workers. Janitors, cleaners, and light truck drivers also experienced increased risk. Those employed in plumbing, heating and air conditioning industries, and sales of nondurable goods (such as paints and varnishes) had an increased risk. Printers, painters, and workers in the food and metal industries had a nonsignificantly increased risk of leukemia. Analyses by specific exposures and histology of leukemia showed that risk of leukemia associated with occupational or industrial exposures may vary by histological type of the disease.

CONCLUSIONS

An increased risk of leukemia among workers employed in agricultural industries, nursing and healthcare workers, and in a few occupations with possible exposure to solvents is consistent with earlier studies. Associations of risk with occupations not observed previously deserve further assessment. Published 2001 Wiley-Liss, Inc.