Urbanization and childhood leukaemia in Taiwan

Maternal medically diagnosed infection and antibiotic prescription during pregnancy and risk of childhood cancer: A population-based cohort study in Taiwan, 2004 to 2015

While associations between maternal infections during pregnancy and childhood leukemia in offspring have been extensively studied, the evidence for other types of childhood cancers is limited. Additionally, antibiotic exposure during pregnancy could potentially increase the risk of childhood cancers. Our study investigates associations between maternal infections and antibiotic prescriptions during pregnancy and the risk of childhood cancer in Taiwan. We conducted a population-based cohort study using the Taiwan Maternal and Child Health Database (TMCHD), linked with national health and cancer registries. The study included 2 267 186 mother-child pairs, and the median follow-up time was 7.96 years. Cox proportional hazard models were utilized to estimate effects. Maternal infections during pregnancy were associated with a moderate increase in the risk of childhood hepatoblastoma (adjusted hazard ratio [HR] = 1.34; 95% confidence interval [CI]: 0.90-1.98) and a weaker increase in the risk of childhood acute lymphoblastic leukemia (ALL) (adjusted HR = 1.15; 95% CI: 0.99-1.35). Antibiotic prescriptions during pregnancy were also associated with an elevated risk of childhood ALL (adjusted HR = 1.30; 95% CI: 1.04-1.63), particularly with tetracyclines (adjusted HR = 2.15; 95% CI: 1.34-3.45). Several specific antibiotics were also associated with an increased risk of hepatoblastoma and medulloblastoma. Children exposed in utero to antibiotic prescription or both infections and antibiotics during pregnancy were at higher risk of developing ALL. Our findings suggest that there are associations between maternal infections, antibiotic use during pregnancy and the risk of several childhood cancers in addition to ALL and highlight the importance of further research in this area.

Assisted Reproductive Technology and Risk of Childhood Cancers

IMPORTANCE

The number of children born through the use of assisted reproductive technology (ART) has been increasing. These children may have higher risks for epigenetic alteration and adverse perinatal outcomes, which may be associated with childhood cancers.

OBJECTIVE

To determine the associations between different modes of conception and childhood cancers and potential mediation by preterm birth and low birth weight.

DESIGN, SETTING, AND PARTICIPANTS

This nationwide, population-based cohort study included registry data from 2 308 016 eligible parents-child triads in Taiwan from January 1, 2004, to December 31, 2017. A total of 1880 children with incident childhood cancer were identified. Data were analyzed between September 1, 2020, and June 30, 2022.

EXPOSURE

Mode of conception, defined as (1) natural conception, (2) subfertility and non-ART (ie, infertility diagnosis but no ART-facilitated conception), or (3) ART (ie, infertility diagnosis and ART-facilitated conception).

MAIN OUTCOMES AND MEASURES

Diagnosis of childhood cancer according to the International Classification of Childhood Cancers, Third Edition.

RESULTS

The mean (SD) paternal and maternal ages were 33.28 (5.07) and 30.83 (4.56) years, respectively. Of the 2 308 016 children, 52.06% were boys, 8.16% were born preterm, and 7.38% had low birth weight. During 14.9 million person-years of follow-up (median, 6 years [IQR, 3-10 years]), ART conception was associated with an increased risk of any type of childhood cancers compared with natural conception (hazard ratio, 1.58; 95% CI, 1.17-2.12) and subfertility with non-ART conception (hazard ratio, 1.42; 95% CI, 1.04-1.95). The increased cancer risk of children conceived with ART was mainly owing to leukemia and hepatic tumor. The increased cancer risk associated with ART conception was not mediated by preterm birth or low birth weight.

CONCLUSIONS AND RELEVANCE

In this cohort study, children conceived via ART had a higher risk of childhood cancers than those conceived naturally and those born to parents with an infertility diagnosis did not use ART. The increased risk could not be explained by preterm birth or low birth weight.

Global, Regional, and National Burden of Cancer in Children Younger Than 5 Years, 1990-2019: Analysis of the Global Burden of Disease Study 2019

OBJECTIVES

To quantify the burden and variation trends of cancers in children under 5 years at the global, regional, and national levels from 1990 to 2019.

METHODS

Epidemiological data for children under 5 years who were diagnosed with any one childhood cancer were obtained from the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) from 1990 to 2019. The outcomes were the absolute numbers and rates of incidence, prevalence, mortality, and disability-adjusted life-years (DALYs) for different types of cancer.

RESULTS

In 2019, 8,774,979.1 incident cases (95% uncertainty interval [UI]: 6,243,599.2 to11,737,568.5) and 8,956,583.8 (6,446,323.9 to 12,364,520.8) prevalent cases of cancer in children under 5 years were identified worldwide; these cancers resulted in 44,451.6 (36,198.7 to 53,905.9) deaths and 3,918,014.8 (3,196,454.9 to 4,751,304.2) DALYs. From 1990 to 2019, although the numbers of incident and prevalent cases only decreased by -4.6% (-7.0 to -2.2) and -8.3% (-12.6 to -3.4), respectively, the numbers of deaths and DALYs clearly declined by -47.8% (-60.7 to -26.4) and -47.7% (-60.7 to -26.2), respectively. In 2019, the middle sociodemographic index (SDI) regions had the highest incidence and prevalence, whereas the low SDI regions had the most mortality and DALYs. Although all of the SDI regions displayed a steady drop in deaths and DALYs between 1990 and 2019, the low-middle and low SDI regions showed increasing trends of incidence and prevalence. Leukemia remained the most common cancer globally in 2019. From 1990 to 2019, the burdens of leukemia, liver cancer, and Hodgkin's lymphoma declined, whereas the incidence and prevalence of other cancers grew, particularly testicular cancer.

CONCLUSIONS

The global childhood cancer burden in young children has been steadily decreasing over the past three decades. However, the burdens and other characteristics have varied across different regions and types of cancers. This highlights the need to reorient current treatment strategies and establish effective prevention methods to reduce the global burden of childhood cancer.

Associations of Physician Characteristics with Sex Difference in Ischemic Heart Disease Incidence among Patients Living with Type 2 Diabetes in Taiwan

(1) Background: Certain non-biological factors are suspected to explain the reduced sex difference in cardiovascular risk after diabetes. This study aimed to assess whether physician characteristics may account for such reduced sex difference. (2) Methods: Totally 10,105 type 2 diabetes patients (including 4962 men and 5143 women) were selected from Taiwan’s National Health Insurance claim data. The three-year period following the first day of clinical visit for type 2 diabetes in 2000 was set as the baseline period. The follow-up was made from the first day after baseline period to date of ischemic heart disease (IHD) incidence or censoring. Cox regression model was used to estimate hazard ratios (HRs) of IHD in relation to physician’s characteristics. (3) Results: The incidence of IHD for men and women was estimated at 17.47 and 15.96 per 1000 person-years, respectively. After controlling for socio-demographic variables and co-morbidity, male patients experienced a significantly higher HR than females for IHD (1.16, 95% Confidence Interval (CI) 1.04 to 1.29). Further adjustment for treatment adherence/continuity and physician characteristics resulted in essentially the same results. (4) Conclusions: Our study provides little support for the notation that physician characteristics may contribute to the reduced sex difference in IHD incidence in patients with type 2 diabetes.

Association between trajectory of severe hypoglycemia and dementia in patients with type 2 diabetes: A population-based study

Background

We aimed to investigate associations between exposure to various trajectories of severe hypoglycemic events and risk of dementia in patients with type 2 diabetes.

Methods

In 2002–2003, 677,618 patients in Taiwan were newly diagnosed as having type 2 diabetes. Among them, 35,720 (5.3%) experienced severe hypoglycemic events during the 3-year baseline period following diagnosis. All patients were followed from the first day after baseline period to the date of dementia diagnosis, death, or the end of 2011. A group-based trajectory model was used to classify individuals with severe hypoglycemic events during the baseline period. Cox proportional hazard models with the competing risk method were used to relate dementia risk to various severe hypoglycemia trajectories.

Results

After a median follow-up 6.70 and 6.10 years for patients with and without severe hypoglycemia at baseline, respectively, 1,952 (5.5%) individuals with severe hypoglycemia and 23,492 (3.7%) without developed dementia during follow-up, for incidence rates of 109.80 and 61.88 per 10,000 person-years, respectively. Four groups of severe hypoglycemia trajectory were identified with a proportion of 18.06%, 33.19%, 43.25%, and 5.50%, respectively, for Groups 1 to 4. Groups 3 (early manifestation but with later decrease) and 4 (early and sustained manifestation) were associated with a significantly increased risk of dementia diagnosis, with a covariate-adjusted subdistribution hazard ratio of 1.22 (95% confidence interval, 1.14–1.31) and 1.25 (95% confidence interval, 1.02–1.54), respectively.

Conclusion

Our analysis highlighted that early manifestation of severe hypoglycemic events may contribute more than does late manifestation to the risk of dementia among individuals newly diagnosed as having type 2 diabetes.

Assessment of Predictive Scoring System for 90-Day Mortality Among Patients With Locally Advanced Head and Neck Squamous Cell Carcinoma Who Have Completed Concurrent Chemoradiotherapy

IMPORTANCE

There is currently no system to predict 90-day morality among patients with locally advanced head and neck squamous cell carcinoma (HNSCC) after the completion of concurrent chemoradiotherapy (CCRT).

OBJECTIVE

To validate the accuracy of a predictive scoring system for 90-day mortality among patients with locally advanced HNSCC who have completed CCRT.

DESIGN, SETTING, AND PARTICIPANTS

This prognostic study included 16 029 patients with HNSCC who completed CCRT between January 2006 and December 2015. Data were extracted from the Taiwan Cancer Registry Database. A risk scoring system was developed based on significant risk factors and corresponding risk coefficients. Data analysis was conducted from June 2018 to February 2019.

EXPOSURES

Mortality within 90 days of completion of definitive CCRT.

MAIN OUTCOMES AND MEASURES

The 90-day mortality rate after completion of CCRT and the accuracy of the scoring system, based on a comparison of mortality rates between training and test data sets.

RESULTS

Among 16 029 patients with locally advanced HNSCC, 1068 (6.66%; 1016 [95.1%] men; mean [SD] age, 55.11 [11.45] years) died before reaching the 90-day threshold, and 14 961 (93.4%; 14 080 [94.1%] men; mean [SD] age, 52.07 [9.99] years) survived. Multivariable analysis revealed that being aged 50 years or older (adjusted hazard ratio [aHR], 1.263; 95% CI, 1.104-1.445; P < .001), being aged 70 years or older (aHR, 2.183; 95% CI, 1.801-2.645; P < .001), having pneumonia (aHR, 1.946; 95% CI, 1.636-2.314; P < .001), having sepsis (aHR, 3.005; 95% CI, 2.503-3.607; P < .001), having hemiplegia (aHR, 1.430; 95% CI, 1.085-1.884; P = .01), having moderate or severe renal disease (aHR, 2.054; 95% CI, 1.643-2.568; P < .001), having leukemia (aHR, 4.541; 95% CI, 1.132-8.207; P = .03), and having non-HNSCC metastatic solid cancers (aHR, 1.457; 95% CI, 1.292-1.644; P < .001) were significant risk factors for 90-day mortality. Risk scores were categorized as very low risk (score of 0), low risk (score 1-3), moderate risk (score 4-6), and high risk (score ≥7), with 90-day mortality rates of 3.37%, 5.00% to 10.98%, 16.15% to 29.13%, and 33.93% to 37.50%, respectively. Mortality rates for patients with the same risk score in the training and test data sets were similar (score of 0, 3.27% vs 3.66%; score of 6, 27.42% vs 25.00%).

CONCLUSIONS AND RELEVANCE

In this prognostic study, a 90-day mortality scoring system accurately predicted 90-day mortality among patients with locally advanced HNSCC who completed CCRT.

Long-Term Outcomes of Pediatric Enterovirus Infection in Taiwan: A Population-Based Cohort Study

Introduction: The major burden of diseases in childhood has shifted from infectious diseases to chronic health conditions in recent decades. Although the rates of infectious diseases have decreased, the incidence of chronic diseases stemming from infectious agents continues to grow. Enterovirus is a major infectious disease of childhood and has been linked to numerous chronic diseases. We analyzed population-based data from Taiwan's National Health Insurance Research Database (NHIRD) to investigate the correlations between enterovirus infection and major chronic health conditions in children. Method: Children diagnosed with enterovirus (EV) infection during 1999-2003 were identified from the Longitudinal Health Insurance Database 2000 (LHID 2000), a subdataset of Taiwan's National Health Insurance Research Database (NHIRD). A total of 14,168 patients were selected after excluding patients with existing chronic diseases and missing data. Another 14,168 children matched by age and sex were selected as the control group. Five primary outcomes, including attention deficit and hyperactivity disorder (ADHD), epilepsy, asthma, allergic rhinitis, and atopic dermatitis, were recorded. Results: The risks of ADHD, asthma, allergic rhinitis, and epilepsy were significantly increased in the EV group compared with the control group. The risk of atopic dermatitis was significantly increased in the crude model. However, there were no significant differences in the adjusted model. The risks of ADHD, asthma, allergic rhinitis, and epilepsy were also significantly increased in patients with severe EV infection compared with patients with non-severe EV infection. Conclusion: Chronic diseases, such as ADHD, epilepsy, asthma, allergic rhinitis, and atopic dermatitis were shown to be associated with enterovirus infection during childhood. EV infection during early childhood might have long-term public health implications and thus prevention strategies should be implemented.

Geographic Variation in Cancer Incidence among Children and Adolescents in Taiwan (1995-2009)

BACKGROUND

Evidence from our recent study suggested that the overall trend for cancer incidence in children and adolescents has been increasing in Taiwan.

METHODS

To analyze geographic variations in this trend, cancer frequencies and incidence rates of disease groups were quantified according to geographic areas among 12,633 patients aged <20 years during 1995-2009 by using the population-based Taiwan Cancer Registry. Three geographic levels were defined, namely county or city, region (Northern, Central, Southern, and Eastern Taiwan), and local administrative area (special municipality, provincial city, county-administered city, township, and aboriginal area).

RESULTS

Of the regions, Northern Taiwan had the highest incidence rate at 139.6 per million person-years, followed by Central (132.8), Southern (131.8), and Eastern (128.4) Taiwan. Significantly higher standardized rate ratios (SRRs) were observed in Northern Taiwan (SRR = 1.06, 95% confidence interval [CI] = 1.02-1.10) and at the township level (SRR = 1.07, 95% CI = 1.03-1.11). Of the cities or counties, New Taipei City yielded the highest SRR (1.08), followed by Taipei City (SRR = 1.07). A comparison of the rates in the four regions and the remainder of Taiwan according to cancer type revealed that only the rate of neuroblastomas in Eastern Taiwan was significantly low. Trend analysis showed that the most significant increase in incidence rate was observed at the township level, with an annual percent change of 1.8% during the 15-year study period.

CONCLUSIONS

The high rate of childhood cancer in Northern Taiwan and at the township level deserves further attention. The potential impacts of environmental factors on the upward trend of childhood cancer incidence rate in townships warrant further investigation.

Perinatal and childhood risk factors for early-onset type 1 diabetes: a population-based case-control study in Taiwan

BACKGROUND

Certain factors originating from the perinatal and childhood periods are suspected of contributing to the recent increasing trend of childhood type 1 diabetes (T1D) incidence. This study sought to investigate the relationships between various perinatal and childhood risk factors and T1D incidence in young children (<10 years).

METHODS

We used a nested case-control design based on 1,478,573 live births born in 2000-05 in Taiwan. Cases were 632 incident cases of T1D between 2000 and 2008. Ten matched controls for each case were randomly selected. Information on various perinatal risk factors was also identified from claim data. Multiple conditional logistic regression was employed to estimate odds ratio (OR) and 95 confidence interval (CI) of T1D.

RESULTS

Childhood infection was significantly associated with an increased risk of T1D (OR = 1.46, 95% CI = 1.23-1.73). Increased risk of T1D was also noted in children born to younger mothers (<25 years) (OR = 1.94, 95% CI = 1.34-2.81), older fathers (>30 years) (OR = 1.56 (95% CI = 1.16-2.10) to 1.57 (95% CI = 1.19-2.05), mothers with Caesarean section (CS) (OR = 2.35, 95% CI = 1.52-3.64), and mothers with gestational diabetes mellitus (OR = 4.36, 95% CI = 2.76-7.77). Fathers with T1D (OR = 7.36, 95% CI = 1.02-57.21) or type 2 diabetes (OR = 1.54, 95% CI = 1.04-2.26) were observed to substantially increase the risk of offspring T1D.

CONCLUSIONS

Certain modifiable perinatal factors such as infection and CS may predispose incidence of T1D in young children.

Sociodemographic and meteorological correlates of sudden infant death in Taiwan

BACKGROUND

This study was designed, using three national datasets including the Taiwan Death Registry, Taiwan Birth Registry, and National Meteorological Dataset, to examine the sociodemographic, geographic and meteorological correlates of sudden infant death syndrome (SIDS).

METHODS

One thousand, six hundred and seventy-one cases of SIDS occurring between 1994 and 2003, and 8355 matched controls were included in this nested case-control study.

RESULTS

Over the study period, the annual rate of SIDS declined only slightly, with an average annual rate of 57.9/10(5) . Male infants (adjusted odds ratio [AOR], 1.19; 95% confidence interval [CI]: 1.06-1.33), preterm births (AOR, 1.69; 95%CI: 1.33-2.13), low birthweight (AOR, 2.87; 95%CI: 2.30-3.59), and birth order ≥3 (AOR, 1.62; 95%CI: 1.37-1.92) were the demographic risk factors for SIDS. Additionally, paternal age <25 years (AOR, 1.37; 95%CI: 1.09-1.71), urbanization (AOR, 1.46; 95%CI: 1.20-1.78), lower paternal education (elementary and less; AOR, 1.28; 95%CI: 1.01-1.64), and parental age difference >10 years (AOR, 1.72; 95%CI: 1.24-2.39) were also associated with increased risk of SIDS. It was also noted that daily average temperature ranging from 9.2°C to 14.2°C (AOR, 2.10; 95%CI: 1.67-2.64) was associated with the most increased risk, while temperature ≥26.4°C (AOR 0.60, 0.61) was significantly associated with the most reduced risk.

CONCLUSION

Sociodemographic, geographic and meteorological data can be used to identify families in greater need of early guidance and to promote various prevention measures to avoid the occurrence of SIDS.

A population-based case-control study of radiofrequency exposure in relation to childhood neoplasm

This population-based case-control study in Taiwan considered incident cases aged 15 years or less and admitted in 2003 to 2007 for all neoplasm (ICD-9-CM: 140-239) (n=2606), including 939 leukemia and 394 brain neoplasm cases. Controls were randomly selected, with a case/control ratio of 1:30 and matched on year of birth, from all non-neoplasm children insured in the same year when the index case was admitted. Annual summarized power (ASP, watt-year) was calculated for each of the 71,185 mobile phone base stations (MPBS) in service between 1998 and 2007. Then, the annual power density (APD, watt-year/km(2)) of each township (n=367) was computed as a ratio of the total ASP of all MPBS in a township to the area of that particular township. Exposure of each study subject to radio frequency (RF) was indicated by the averaged APD within 5 years prior to the neoplasm diagnosis (cases) or July 1st of the year when the index case was admitted (controls) in the township where the subject lived. Unconditional logistic regression model with generalized estimation equation was employed to calculate the covariate-adjusted odds ratio [AOR] of childhood neoplasm in relation to RF exposure. A higher than median averaged APD (approximately 168 WYs/km(2)) was significantly associated with an increased AOR for all neoplasms (1.13; 1.01 to 1.28), but not for leukemia (1.23; 0.99 to 1.52) or brain neoplasm (1.14, 0.83 to 1.55). This study noted a significantly increased risk of all neoplasms in children with higher-than-median RF exposure to MPBS. The slightly elevated risk was seen for leukemia and brain neoplasm, but was not statistically significant. These results may occur due to several methodological limitations.

An examination, with a meta-analysis, of studies of childhood leukaemia in relation to population mixing

Background:

Marked influxes of people into rural areas, termed rural population mixing (PM), have been associated with excesses of childhood leukaemia (CL), consistent with mini-epidemics of a mainly immunising, subclinical infection to which CL is a rare response. For such situations of rural PM would promote contacts between infected and susceptible individuals, the latter tending to have a higher than average prevalence in rural or isolated areas. Confusion has arisen from some workers applying the term PM to non-rural situations lacking known recent change.

Methods:

Available PM studies using the original definition of influxes were examined, a meta-analysis carried out of studies of CL in relation to exposure to high levels of rural PM, and also a detailed analysis by age group.

Results:

The meta-analysis of 17 studies shows a significant CL excess in association with rural PM: overall relative risk (RR) at ages 0–14: 1.57; 95% confidence interval 1.44–1.72; at 0–4 years 1.72 (1.54–1.91). This contrasts with the absence of an excess of CL in similarly exposed urban areas (RR 1.00; 0.93–1.07), pointing to a high level of immunity there. The mixed results of studies using other definitions of PM were summarised. The excess associated with rural PM below age 2 years (RR 1.51; 1.17, 1.92) was not appreciably different from that at later childhood ages.

Conclusion:

Much of the inconsistency among studies ostensibly about CL and PM reflects the use of definitions other than that originally proposed. The broad similarity of the CL excess below age 2 with that at older childhood ages is inconsistent with the Greaves’ delayed infection hypothesis, since any infection underlying the former is difficult to consider as delayed.

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.

Childhood leukemia and traffic air pollution in Taiwan: petrol station density as an indicator

To investigate the relationship between traffic air pollution exposure and development of childhood leukemia (14 yr of age or younger), a matched case-control study was conducted using childhood deaths that occurred in Taiwan from 1996 through 2006. Data on all eligible childhood leukemia deaths were obtained from the Bureau of Vital Statistics of the Taiwan Provincial Department of Health. The control group consisted of children who died from causes other than neoplasms or diseases that were not associated with respiratory complications. The controls were pair matched to the cancer cases by gender, year of birth, and year of death. Each matched control was selected randomly from the set of possible controls for each case. Data on the number of petrol stations in study municipalities were collected from the two major petroleum supply companies, Chinese Petroleum Corporation (CPC) and Formosa Petrochemical Corporation (FPCC). The petrol station density (per square kilometer) (PSD) for study municipalities was used as an indicator of a subject's exposure to benzene and other hydrocarbons present in evaporative losses of petrol or to air emissions from motor vehicles. The subjects were divided into tertiles according to PSD in their residential municipality. The results showed that there was a significant exposure-response relationship between PSD and the risk of leukemia development in young children after controlling for possible confounders. The findings of this study warrant further investigation of the role of traffic air pollution exposure in the etiology of childhood leukemia.

Does population mixing measure infectious exposure in children at the community level?

Epidemiological studies focusing on the etiology of childhood chronic diseases have used population mixing as a proxy for the level of infection circulating in a community. We compared different measures of population mixing (based on residential migration and commuting) and other demographic variables, derived from the United Kingdom Census, with hospital inpatient data on infections from two Government Office Regions in England (Eastern and the West Midlands) to inform the development of an infectious disease proxy for future epidemiological studies. The association between rates of infection and the population mixing measures was assessed, using incidence rate ratios across census areas, from negative binomial regression. Commuting distance demonstrated the most consistent association with admissions for infections across the two regions; areas with a higher median distance travelled by commuters leaving the area having a lower rate of hospital admissions for infections. Deprived areas and densely populated areas had a raised rate of admissions for infections. Assuming hospital admissions are a reliable indicator of common infection rates, the results from this study suggest that commuting distance is a consistent measure of population mixing in relation to infectious disease and deprivation and population density are reliable demographic proxies for infectious exposure. Areas that exhibit high levels of population mixing do not necessarily possess raised rates of hospital admissions for infectious disease.

What do epidemiologists mean by 'population mixing'?

There is growing evidence that some chronic diseases are caused, or promoted, by infectious disease. 'Population mixing' has been used as a proxy for the range and dose of infectious agents circulating in a community. Given the speculation over the role of population mixing in many chronic diseases, we review the various methods used for measuring population mixing, and provide a classification of these. We recommend that authors fulfill two criteria in publications: measures are demonstrably associated with the putative risk factors for which population-mixing is acting as a proxy and fundamental characteristics of the chosen measures are clearly defined.

Association of childhood leukemia with residential exposure to petrochemical air pollution in taiwan

To investigate the relationship between petrochemical air pollution and childhood leukemia (19 yr of age or younger), the authors conducted a matched case-control study using childhood deaths that occurred in Taiwan from 1995 through 2005. Data on all eligible childhood leukemia deaths were obtained from the Bureau of Vital Statistics of the Taiwan Provincial Department of Health. The control group consisted of children who died from causes other than neoplasms or diseases that were not associated with respiratory problems. The controls were pair matched to the cases by sex, year of birth, and year of death. Each matched control was selected randomly from the set of possible controls for each case. The proportion of a municipality's total population employed in the petrochemical industry in a municipality was used as an indicator of a resident's exposure to air emissions from the petrochemical industry. The subjects were divided into three levels (< or =25th percentile; 25th-75th percentile; > 75th percentile) according to the levels of the index just described. After controlling for possible confounders, results showed that children who lived in the group of municipalities characterized by the highest levels of petrochemical air pollution had a statistically significant higher risk of developing leukemia than the group that lived in municipalities with the lowest petrochemical air pollution levels. The results of this study shed important light on the relationship between the Taiwan petrochemical industry and human health risks.

Socio-economic inequalities in low-birth weight, full-term babies from singleton pregnancies in Taiwan

OBJECTIVES

This study investigated the chronological trend of low-birth weight in full-term babies (TLBW) in Taiwan in the 1980s and 1990s when the nation experienced a rapid economic advancement, and assessed the association between TLBW and parental education and marital status.

DESIGN

Data from liveborn singletons from Taiwan's birth registry, born between 1978 and 1997, were used to calculate overall and socio-economic factor-specific rates of TLBW for every 2-year interval in this 20-year period.

METHODS

Logistic regression models were used to assess the trend of TLBW rates, and the interaction between secular time, selected demographic factors and other predictors.

RESULTS

Among 6,159,070 full-term, liveborn singletons, 208,729 were TLBW. The average annual rate of TLBW was 3.39% in the study period. The period-specific TLBW declined monotonically from 4.41% in 1978-1979 to 2.49% in 1996-1997, representing a 43% deduction. Multiple logistic regression demonstrated persistent declining trends irrespective of the educational level or marital status of the parents. However, the decline was slower for populations of lower socio-economic status, such as less-educated parents and unmarried mothers, which enhanced the inequalities of TLBW risk across populations. The TLBW risk ratios of the least-educated mothers to the most-educated mothers increased from 1.43 in 1978-1979 to 2.05 in 1996-1997. Unmarried status was an independent predictor of elevated risk of TLBW.

CONCLUSIONS

The association between socio-economic inequality and the risk of TLBW infants was sustained over the 1980s and 1990s in Taiwan. Interventions are necessary to promote antenatal care and educational attainment, particularly for lower socio-economic and socially deprived populations in Taiwan.

Population mixing, socioeconomic status and incidence of childhood acute lymphoblastic leukaemia in England and Wales: analysis by census ward

In this population-based study of acute lymphoblastic leukaemia (ALL) diagnosed among children aged under 15 years in England and Wales during 1986-1995, we analysed incidence at census ward level in relation to a range of variables from the 1991 census, which could be relevant to theories of infectious aetiology. 'Population-mixing' measures, used as surrogates for quantity and diversity of infections entering the community, were calculated from census data on the origins and destinations of migrants in the year before the census. Incidence at ages 1-4 years tended independently to be higher in rural wards, to increase with the diversity of origin wards from which in-migrants had moved during the year before the census, and to be lower in the most deprived areas as categorised by the Carstairs index. This last association was much weaker when urban/rural status and in-migrants' diversity were allowed for. There was no evidence of association with population mixing or deprivation for ALL diagnosed at ages 0 or 5-14 years. The apparent specificity to the young childhood age group suggests that these associations are particularly marked for precursor B-cell ALL, with the disease more likely to occur when delayed exposure to infection leads to increased immunological stress, as predicted by Greaves. The association with diversity of incomers, especially in rural areas, is also consistent with the higher incidence of leukaemia predicted by Kinlen, where population mixing results in below average herd immunity to an infectious agent.

Childhood leukemia development and correlation with traffic air pollution in Taiwan using nitrogen dioxide as an air pollutant marker

To investigate the relationship between traffic air pollution and development of childhood leukemia (14 yr of age or younger), studies were conducted on a matched cancer case-control cohort using childhood deaths that occurred in Taiwan from 1995 through 2005. Data on all eligible childhood leukemia deaths were obtained from the Bureau of Vital Statistics of the Taiwan Provincial Department of Health. The control group consisted of children who died from causes other than neoplasms or from diseases that were not associated with respiratory complications. The controls were pair matched to the cases by gender, year of birth, and year of death. Each matched control was selected randomly from the set of possible controls for each case. Air quality data for recorded concentrations of nitrogen dioxide (NO2) from study municipalities for 1995-2005 were obtained as an indicator of a subject's exposure to air emissions from motor vehicles. The subjects were divided into tertiles according to the levels of NO2 in their residential municipality. The results showed that there was a significant exposure-response relationship between exposure to traffic exhaust pollutants and the risk of leukemia among young children after controlling for possible confounders. The findings of this study warrant further investigation of the role of traffic air pollution in the etiology of childhood leukemia.

Association of brain cancer with residential exposure to petrochemical air pollution in Taiwan

To investigate the relationship between petrochemical air pollution and brain cancer (29 yr of age or younger), the authors conducted a matched case-control study using deaths that occurred in Taiwan from 1995 through 2005. Data on all eligible brain cancer deaths were obtained from the Bureau of Vital Statistics of the Taiwan Provincial Department of Health. The control group consisted of subjects who died from causes other than neoplasms or diseases that were not associated with respiratory problems. The controls were pair matched to the cases by sex, year of birth, and year of death. Each matched control was selected randomly from the set of possible controls for each case. The proportion of a municipality's total population employed in the petrochemical industry in a municipality was used as an indicator of a resident's exposure to air emissions from the petrochemical industry. The subjects were divided into tertiles according to the levels of the index just described. Subjects who lived in the group of municipalities characterized by the highest levels of petrochemical air pollution had a statistically significant higher risk of developing brain cancer than the group that lived in municipalities with the lowest petrochemical air pollution levels after controlling for possible confounders (OR = 1.65, 95% CI = 1.00-2.73). The findings of this study warrant further investigation of the role of petrochemical air pollution in the etiology of brain cancer.

Residential mobility and risk of childhood acute lymphoblastic leukaemia: an ecological study

We conducted an ecological analysis of childhood acute lymphoblastic leukaemia-incidence data from children ⩽5 years old during 1992–1998 from the Surveillance, Epidemiology, and End Results Program in 200 counties and Hawaii. The response variable was the count of cases in each county race–sex stratum, examined in relation to data from the United States Census and the United States Department of Agriculture. The final models for both sexes included race, proportion moved during 1985–1990, and proportion of households with income ⩾$5000 as potential predictors. Incidence was lower among black boys (rate ratio (RR)=0.5) and black girls (RR=0.4) than among other children of the same sex; no other significant racial differences were detected. Incidence was elevated among males (but not females) residing in counties where ⩾50% of the population relocated (RR=1.5) and among females (but not males) residing in counties where <6% of the households had incomes <$5000 (RR=1.5). These sex differences in risk factors were unexpected.

Socioeconomic status and childhood leukaemia: a review

BACKGROUND

A long-held view links higher socioeconomic status (SES) to higher rates of childhood leukaemia. Some recent studies exhibit associations in the opposite direction.

METHODS

We reviewed journal literature through August 2002 for associations between childhood leukaemia and socioeconomic measures. We determined the direction of each association and its P-value. We described the results with regard to study design, calendar period, geographic locale, and level of the socioeconomic measures (individual or ecological). For measures with sufficient number of results, we computed summary P-values across studies.

RESULTS

Case-control studies conducted in North America since 1980 have involved subject interviews or self-administered questionnaires and have consistently reported inverse (negative) associations of childhood leukaemia with individual-level measures of family income, mother's education, and father's education. In contrast, associations have been consistently positive with father's occupational class in record-based case-control studies and with average occupational class in ecological studies.

CONCLUSIONS

Connections of SES measures to childhood leukaemia are likely to vary with place and time. Validation studies are needed to estimate SES-related selection and participation in case-control studies. Because different socioeconomic measures (such as income and education) and individual-level and ecological-level measures may represent different risk factors, we advise researchers to report these measures separately rather than in summary indices of social class.

Urbanisation and incidence of acute lymphocytic leukaemia among United States children aged 0-4

Acute lymphocytic leukaemia (ALL) incidence among children under 5 years of age was examined, utilising data from 24 United States cancer registries. County-based incidence rates among white children were compared across four levels of urbanisation: large and small metropolitan counties, and adjacent and nonadjacent rural counties. In metropolitan areas, the incidence of ALL was lower among blacks (rate ratio (RR)=0.38, confidence interval (CI)=0.33–0.44) and among Asians/Pacific Islanders (RR=0.78, CI=0.63–0.97) than among whites. Among white children, the incidence of ALL decreased across the four strata of urbanisation, from 67 to 62 to 65 to 54 cases per million person-years at-risk (two-sided trend P=0.009), such that rates were significantly lower in the most remote rural counties than in the most populous metropolitan counties (RR=0.80, 95% CI=0.70–0.91).

Allergy and infectious disease histories and the risk of childhood acute lymphoblastic leukaemia

Infectious disease histories were evaluated in a population-based case-control study of childhood acute lymphoblastic leukaemia (ALL) as it has been hypothesised that delays in early infections are associated with an increased risk of disease. Allergy histories were also assessed as part of a broader evaluation of the role of immune factors in ALL. Cases (n = 255) were diagnosed between 1980 and 1991 at one of four referral centres in a 31-county area of New York State; controls (n = 760) were a random sample of live births from the same region, frequency matched to cases by sex, race and birth year. Data were collected by mailed questionnaire, completed by case and control parents in 1995. Allergy and infectious histories before the age at leukaemia diagnosis for cases and an equivalent age for controls were evaluated. The adjusted odds ratio and 95% confidence interval [CI] associated with a positive history of any allergy was 0.58 [95% CI 0.38, 0.88] compared with a negative allergy history. The occurrence of several common childhood illnesses before 25 months of age and ALL were assessed, with both weak positive and weak inverse associations observed. Overall, these analyses provide little support for the hypothesis that infection delay in early life is associated with an increased risk of ALL. Children with positive allergy histories reported significantly more infections than those with negative histories; however, effect modification of the infection-ALL associations by child allergy history was not observed. Nonetheless, these observations suggest the importance of assessing both allergy and infectious histories and their possible interactions when evaluating the association between these immune factors and childhood ALL.

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.

Probability estimates for the unique childhood leukemia cluster in Fallon, Nevada, and risks near other U.S. Military aviation facilities

A unique cluster of childhood leukemia has recently occurred around the city of Fallon in Churchill County, Nevada. From 1999 to 2001, 11 cases were diagnosed in this county of 23,982 people. Exposures related to a nearby naval air station such as jet fuel or an infectious agent carried by naval aviators have been hypothesized as potential causes. The possibility that the cluster could be attributed to chance was also considered. We used data from the Surveillance, Epidemiology, and End Results Program (SEER) to examine the likelihood that chance could explain this cluster. We also used SEER and California Cancer Registry data to evaluate rates of childhood leukemia in other U.S. counties with military aviation facilities. The age-standardized rate ratio (RR) in Churchill County was 12.0 [95% confidence interval (CI), 6.0-21.4; p = 4.3 times symbol 10(-9)]. A cluster of this magnitude would be expected to occur in the United States by chance about once every 22,000 years. The age-standardized RR for the five cases diagnosed after the cluster was first reported was 11.2 (95% CI, 3.6-26.3). In contrast, the incidence rate was not increased in all other U.S. counties with military aviation bases (RR = 1.04; 95% CI, 0.97-1.12) or in the subset of rural counties with military aviation bases (RR = 0.72; 95% CI, 0.48-1.08). These findings suggest that the Churchill County cluster was unlikely due to chance, but no general increase in childhood leukemia was found in other U.S. counties with military aviation bases.

Perinatal exposure to infection and risk of childhood leukemia

BACKGROUND

A population-based case-control study was conducted to investigate the association between childhood leukemia and infectious exposures during pregnancy and early neonatal period.

PROCEDURE

Children born and diagnosed with leukemia between 1973 and 1989 in Sweden (578 lymphatic, 74 myeloid) were selected as cases. One control was randomly selected for each case and individually matched by sex, month, and year of birth. Children with Down's syndrome were excluded. Exposure data were blindly abstracted from antenatal, obstetric, and other standardized medical records. Odds ratios (OR) and 95% confidence intervals (CI) were calculated by conditional logistic regression.

RESULTS

A history of maternal infection was not significantly associated with childhood leukemia, OR = 1.25 (95% CI 0.95-1.65). Maternal lower genital tract infection significantly increased the risk of childhood leukemia, OR = 1.78 (95% CI 1.17-2.72), and especially for children over 4 years of age at diagnosis, OR = 2.01 (95% CI 1.12-3.80). Neonatal infection was not associated with the risk of leukemia. The results remained unaltered after adjustment for potential confounders, and separate analyses for myeloid and lymphoid leukemia.

CONCLUSIONS

We could document an association between exposure to maternal lower genital tract infection in utero, and a subsequent risk for childhood leukemia, which indicate the importance of an early exposure.

Early child-care and preschool experiences and the risk of childhood acute lymphoblastic leukemia

An infectious etiology for childhood acute lymphoblastic leukemia (ALL) has been suggested, yet few studies have focused on the role of early child care. Day-care histories were examined in a case-control study of ALL in New York State. Cases (n = 255) were diagnosed at one of four referral centers between 1980 and 1991; controls (n = 760) were randomly selected from livebirths in the 31 counties served by the referral centers. Self-administered questionnaires were mailed to the parents of cases and controls in 1995. Day-care histories were censored at the age of diagnosis for cases and at an equivalent date for controls. The odds ratio for children who stayed at home compared with those who attended day care for >36 months was 1.32 (95% confidence interval (CI): 0.70, 2.52); the odds ratios for 1-18 and 19-36 months of day care were 1.74 (95% CI: 0.89, 3.42) and 1.32 (95% CI: 0.64, 2.71), respectively. Elimination of cases with T-cell ALL enhanced the risk. Starting care at an earlier age was not associated with a decreased risk of ALL. These findings do not support the hypothesis that infrequent contact with peers during early childhood could delay exposure to infectious diseases and increase the risk of ALL.