A Simulation Study of Relative Efficiency and Bias in the Nested Case-Control Study Design

PURPOSE

The nested case-control study design, in which a fixed number of controls are matched to each case, is often used to analyze exposure-response associations within a cohort. It has become common practice to sample four or five controls per case; however, previous research has shown that in certain instances, significant gains in relative efficiency can be realized when more controls are matched to each case. This study expanded upon this and investigated the effect of (i) the number of cases, (ii) the strength of the exposure-response, and (iii) the skewness of the exposure distribution on the bias and relative efficiency of the conditional likelihood estimator from a nested case-control study.

METHODS

Cohorts were simulated and analyzed using conditional logistic regression.

RESULTS

The relative efficiency decreased and bias away from the null increased, as the true exposure-response parameter increased and the skewness of the exposure distribution of the risk-sets increased. This became more pronounced when the number of cases in the cohort was small.

CONCLUSIONS

Gains in relative efficiency and a reduction in bias can be realized by sampling more than four or five controls per case generally used, especially when there are few cases, a strong exposure-response relation, and a skewed exposure variable.

Abstract 1153: TGFβR1 germline variant Int7G24A but not TGFβR1*6 increases risk for colon cancer

Transforming growth factor beta (TGF-β) regulates many processes associated with tumor initiation and progression including proliferation, differentiation, migration, cell survival, angiogenesis, and immunosurveillance. The TGF-β signal is transduced by a membrane-bound serine-threonine kinase receptor complex including TGF-β type I and type II receptors. Germline variations in the gene for transforming growth factor beta receptor 1(TGFβR1), a G-to-A single nucleotide polymorphism within intron 7 of the TGFβR1 gene called Int7G24A, and TGFβR1*6A, a nine base pair deletion that occurs in the coding region in exon 1 of the TGFβR1 gene, have been associated with progression and/or initiation of cancers of the kidney and bladder, lung, and breast; however, the association of TGFβR1*6A and Int7G24A with colon cancer is controversial. Approximately 141,000 new cases of colorectal cancer (CRC) will be diagnosed in the US during 2012 and there will be more than 69,000 CRC related deaths. Detection of CRC at early stages is the key to survival, hence we sought to determine a possible association of TGFβR1*6A and Int7G24A with CRC risk. These two germline variants in TGFβR1 were analyzed by capillary electrophoresis in DNA extracted from FFPE archived specimens of normal tissues from 253 patients with colorectal neoplasms and 219 patients who never developed any form of cancer. We found that 46.5% of patients with CIS (stage 0), 46.7% of patients with invasive CRC (Stages I & II) and 46.7% of patients with metastatic CRC (Stages III & IV) were carriers of Int7G24A, compared to 24.7% of patients without any cancer, and this difference was highly significant (p < 0.0001). In contrast the prevalence of Int7G24A in people with benign adenomas who never developed cancer (13.3%) did not differ significantly from non-cancer controls. TGFβR1*6A, was not associated with CRC at any stage compared to non-cancer controls (p = 0.2163). Importantly, the prevalence of TGFβR1*6A in benign adenoma patients that did not develop cancer was significantly higher (33.3%) than in patients with CIS (9.3%, p = 0.02) or metastatic CRC (12.0%, p = 0.03), a finding that is consistent with recent studies of human CRC reporting that tumors with TGFβR1*6A have a lower degree of genetic instability. Neither variant was associated significantly with reduced survival; however, nearly 75% of patients with TGFβR1*6A survived compared to 50% with Int7G24A. We conclude that Int7G24A is associated with increased risk for all stages of CRC whereas TGFβR1*6A is not. These results suggest that Int7G24A may be a biomarker to aid in identification of people at a higher risk for developing CRC thereby promoting CRC detection at early stages and increased CRC survival.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1153. doi:1538-7445.AM2012-1153

Abstract A237: Elevated Mnk kinase activity is associated with malignant progression and reduced patient survival in human prostate cancer and can be therapeutically inhibited in human prostate cancer cells by the novel, orally bioavailable Mnk inhibitor cercosporamide

In a wide variety of malignancies, progressive disease and reduced patient survival have been linked to increased function of eukaryotic translation initiation factor 4E (eIF4E), which selectively enhances the translation of potent growth and survival factors and oncoproteins (e.g. c-myc, VEGF, cyclin D1, Mcl-1, MMP-9, etc.). Recent published reports have shown that the oncogenic activity of eIF4E is critically dependent on the activity of the MNK kinases (Map kinase interacting kinase 1 and 2), which phosphorylate eIF4E at S209 (p4ES209). Increased p4ES209 has been linked to a variety of advanced cancers, notably head and neck and non-small cell lung cancers. Herein, we report that p4ES209 is significantly elevated in human prostate cancer (CaP) tissues (n=133) and associated with reduced patient survival. p4ES209 is elevated In both low grade (Gleason score ≤ 6) and high grade (Gleason score ≥ 7) CaP vs. adjacent normal prostate tissue (BPH) (p < 0.02 and p < 0.0001, respectively). Elevated p4ES209 in invasive CaP is related to significantly reduced patient survival (p = 0.0216) and increased risk of death from CaP (hazard ratio = 2.729). Moreover, p4ES209 is evident in the LNCaP, LNAI, CWR22Rv1 CaP cell lines, with levels being highest in the castrate-resistant cells (LNAI and CWR22Rv1). shRNA-mediated knock-down of MNK 1 and 2 reduced p4ES209 levels and specifically triggered apoptosis. Similarly, treatment of these cell lines with the novel, orally-bioavailable MNK inhibitor, cercosporamide, reduced p4ES209 in a dose-dependent manner and induced apoptosis coincident with reduced expression of key translationally controlled proteins (e.g. Mcl-1). Further, oral administration of this inhibitor can suppress p4ES209 in normal mouse tissues and in xenografted human cancers within 30 minutes, lasting at least 4 hours in tumor tissue. These data demonstrate the utility of cercosporamide in probing MNK function in vitro and in vivo and highlight the potential utility of targeting MNK for prostate cancer therapy.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr A237.

Infrastructure for quality transformation: measurement and reporting in veterans administration intensive care units

BACKGROUND Veterans Health Administration (VA) intensive care units (ICUs) develop an infrastructure for quality improvement using information technology and recruiting leadership. METHODS Setting Participation by the 183 ICUs in the quality improvement program is required. Infrastructure includes measurement (electronic data extraction, analysis), quarterly web-based reporting and implementation support of evidence-based practices. Leaders prioritise measures based on quality improvement objectives. The electronic extraction is validated manually against the medical record, selecting hospitals whose data elements and measures fall at the extremes (10th, 90th percentile). results are depicted in graphic, narrative and tabular reports benchmarked by type and complexity of ICU. RESULTS The VA admits 103 689±1156 ICU patients/year. Variation in electronic business practices, data location and normal range of some laboratory tests affects data quality. A data management website captures data elements important to ICU performance and not available electronically. A dashboard manages the data overload (quarterly reports ranged 106-299 pages). More than 85% of ICU directors and nurse managers review their reports. Leadership interest is sustained by including ICU targets in executive performance contracts, identification of local improvement opportunities with analytic software, and focused reviews. CONCLUSION Lessons relevant to non-VA institutions include the: (1) need for ongoing data validation, (2) essential involvement of leadership at multiple levels, (3) supplementation of electronic data when key elements are absent, (4) utility of a good but not perfect electronic indicator to move practice while improving data elements and (5) value of a dashboard.

An epidemiological appraisal instrument - a tool for evaluation of epidemiological studies

In recent years, ergonomics practices have increasingly relied upon the knowledge derived from epidemiological studies. In this regard, there is limited research devoted to the exclusive evaluation of the methodological qualities of ergonomics epidemiological studies. The aim of this study was to develop and test a general purpose 'epidemiological appraisal instrument' (EAI) for evaluating the methodological quality of existing or new ergonomic epidemiological studies using a critical appraisal system rooted in epidemiological principles. A pilot EAI version was developed and tested by a team of epidemiologists/physicians/biostatisticians, with the team leader being both epidemiologist and ergonomist. The pilot version was further tested with regard to other raters with/without a background in epidemiology, biostatistics and ergonomics. A revised version was evaluated for criterion validity and reliability. An assessor with a basic background in epidemiology and biostatistics would be able to correctly respond on four out of five questions, provided that subject matter expertise is obtained on specific items. This may improve with the article's quality. Training may have an effect upon assessors with virtually no background in epidemiology/biostatistics, but with a background in ergonomics. In this latter case, the inter-rater degree of agreement is largely above 90% and assessors can resolve their differences in a subsequent round. The EAI proved to be a valid and reliable appraisal instrument that may be used in various applications, such as systematic reviews and meta-analyses.

Cancer risk among firefighters: a review and meta-analysis of 32 studies

OBJECTIVE

The objective of this study was to review 32 studies on firefighters and to quantitatively and qualitatively determine the cancer risk using a meta-analysis.

METHODS

A comprehensive search of computerized databases and bibliographies from identified articles was performed. Three criteria used to assess the probable, possible, or unlikely risk for 21 cancers included pattern of meta-relative risks, study type, and heterogeneity testing.

RESULTS

The findings indicated that firefighters had a probable cancer risk for multiple myeloma with a summary risk estimate (SRE) of 1.53 and 95% confidence interval (CI) of 1.21-1.94, non-Hodgkin lymphoma (SRE = 1.51, 95% CI = 1.31-1.73), and prostate (SRE = 1.28; 95% CI = 1.15-1.43). Testicular cancer was upgraded to probable because it had the highest summary risk estimate (SRE = 2.02; 95% CI = 1.30-3.13). Eight additional cancers were listed as having a "possible" association with firefighting.

CONCLUSIONS

Our results confirm previous findings of an elevated metarelative risk for multiple myeloma among firefighters. In addition, a probable association with non-Hodgkin lymphoma, prostate, and testicular cancer was demonstrated.

Variation in outcomes in Veterans Affairs intensive care units with a computerized severity measure*

OBJECTIVE

To quantify the variability in risk-adjusted mortality and length of stay of Veterans Affairs intensive care units using a computer-based severity of illness measure.

DESIGN

Retrospective cohort study.

SETTING

A stratified random sample of 34 intensive care units in 17 Veterans Affairs hospitals.

PARTICIPANTS

A consecutive sample of 29,377 first intensive care unit admissions from February 1996 through July 1997.

INTERVENTIONS

Standardized mortality ratio (observed/expected deaths) and observed minus expected length of stay (OMELOS) with 95% confidence intervals were estimated for each unit using a hierarchical logistic (standardized mortality ratio) or linear (OMELOS) regression model with Markov Chain Monte Carlo simulation. We adjusted for patient characteristics including age, admission diagnosis, comorbid disease, physiology at admission (from laboratory data), and transfer status.

MEASUREMENTS AND MAIN RESULTS

Mortality across the intensive care units for the 12,088 surgical and 17,289 medical cases averaged 11% (range, 2-30%). Length of stay in the intensive care units averaged 4.0 days (range, mean unit length of stay 3.0-5.9). Standardized mortality ratio of the intensive care units varied from 0.62 to 1.27; the standardized mortality ratio and 95% confidence interval were <1 for four intensive care units and >1.0 for seven intensive care units. OMELOS of the intensive care units ranged from -0.89 to 1.34 days. In a random slope hierarchical model, variation in standardized mortality ratio among intensive care units was similar across the range of severity, whereas variation in length of stay increased with severity. Standardized mortality ratio was not associated with OMELOS (Pearson's r = .13).

CONCLUSIONS

We identified intensive care units whose indicators for mortality and length of stay differ substantially using a conservative statistical approach with a severity adjustment model based on data available in computerized clinical databases. Computerized risk adjustment employing routinely available data may facilitate research on the utility of intensive care unit profiling and analysis of natural experiments to understand process and outcome links and quality efforts.

Lower back disorders among forklift operators: an emerging occupational health problem?

BACKGROUND

Most studies focusing on the occupational hazards associated with forklift operation have examined risks of fatalities and traumatic injuries. Few studies have examined the magnitude of risk of musculoskeletal disorders (MSDs). We review and critically appraise the epidemiological studies conducted on forklift operators in relation to MSDs, such as lower back pain and neck problems.

METHODS

A comprehensive search of databases resulted in the identification of seven epidemiological studies that addressed MSDs. A critical appraisal of these studies was conducted using epidemiological principles and a meta-analysis approach that involved the use of the confidence limit method to determine an overall "meta-odds ratio."

RESULTS

The methodological quality of these studies ranged from "marginal" to "average" with the exception of one study, which was considered "good." The meta-odds ratio for lower back pain among forklift operators was 2.13 (95% CI: 1.57, 2.87).

CONCLUSIONS

Our results suggest that forklift operators are at increased risk of lower back pain. Additional high quality epidemiological studies are needed in the US, however, to determine the magnitude of risk for MSDs. In this regard, studies should address not only lower back pain among forklifts operators, but also neck pain. A full exposure assessment of physical and non-physical factors in these studies is needed.

The relationship between protective and risk characteristics of acting and experienced workload, and musculoskeletal disorder cases among nurses

PROBLEMS

Limited research is available on the acting (work characteristics) and experienced (perceived stress) workload of nurses. The relationship between risk and protective characteristics of work-related factors and the prevalence of musculoskletal symptoms in different body regions is also unclear.

METHODS

The study was a cross-sectional design with 97 female registered nurses working in a hospital setting. Two surveys were used to document the workload exposure of the nurses. One survey consisted of 148 items aimed to measure the acting workload variables from the environment; the other survey included 33 items that were aimed to measure the nurses' experienced workload. The musculoskeletal outcomes were documented with a modified version of the Nordic Musculoskeletal Symptom Survey.

RESULTS

Factor analyses revealed three factors that accounted for 56% of the total variance. Factor 1 (i.e., integrated experienced energy replenishment/expenditure) represented the psychological effects of work characteristics, effort, perceived risk, and performance. Factor 2 (i.e., acting energy replenishment/expenditure) consisted of non-physical variables of the work characteristics, while Factor 3 (i.e., acting energy expenditure) included both acting and experienced workload. Logistic regression analyses indicated that Factor 3 was significantly associated with the musculoskeletal symptoms of lower and upper back, hands/wrists, and knees/lower legs (odds ratios > 1.0). Factor 2 was significantly associated with the musculoskeletal symptoms of the upper back and knees/lower legs (odds ratios < 1.0).

SUMMARY

Both the acting and experienced workloads exhibited associations with musculoskeletal outcomes in the lower back, upper back, hands/wrists, and knees/lower legs in terms of risk and protective effects.

An intronic variant of the TGFBR1 gene is associated with carcinomas of the kidney and bladder

TGF-beta signaling is frequently perturbed in many human cancers, including renal cell carcinomas (RCCs) and transitional cell carcinomas (TCCs) of the bladder. Genetic alterations of the TGF-beta type 1 receptor (TGFBR1) may contribute to these perturbations. We therefore examined variations in the TGFBR1 gene by PCR, SSCP and RFLP in carcinomas of the urinary system and in tissues from noncancer, age-matched controls. A G-->A variant 24 bp downstream of the exon/intron 7 boundary of the TGFBR1 gene (Int7G24A) was evident in patients with RCC (46.5%, n = 86) and bladder and upper urinary tract TCC (49.2%, n = 65) significantly more frequently than in age-matched controls (28.3%, n = 113, p < 0.002 by chi2 test). Moreover, 8 homozygous variant carriers were found in the cancer groups, whereas not a single homozygous variant carrier was found in the control group. The Int7G24A allele (both heterozygous G/A and homozygous A/A carriers) was associated with increased RCC incidence (OR = 2.20, 95% CI 1.22-3.96) and TCC incidence (OR = 2.45, 95% CI 1.89-3.16). One somatic mutation of serine to phenylalanine at codon 57 of the TGFBR1 gene was confirmed in an upper urinary tract TCC. In conclusion, the Int7G24A variant in the TGFBR1 gene is significantly more frequent in patients with RCC and TCC than normal age-matched controls, suggesting that it may represent a risk factor for the development of kidney and bladder carcinomas.

Mortality analyses in a cohort of 18 235 ethylene oxide exposed workers: follow up extended from 1987 to 1998

AIMS

To extend mortality follow up from 1987 to 1998 for cohort of 18 235 men and women exposed to ethylene oxide.

METHODS

Standard mortality follow up, life table and Cox regression analysis.

RESULTS

There were 2852 deaths, compared with 1177 in the earlier 1987 follow up. There was no overall excess of haematopoietic cancers combined or of non-Hodgkin's lymphoma. However, internal exposure-response analyses found positive trends for haematopoietic cancers which were limited to males (15 year lag). The trend in haematopoietic cancer was driven by lymphoid tumours (non-Hodgkin's lymphoma, myeloma, lymphocytic leukaemia), which also have a positive trend with cumulative exposure for males with a 15 year lag. Haematopoietic cancer trends were somewhat weaker in this analysis than trends in the earlier follow up, and analyses restricted to the post-1987 data did not show any significant positive trends (exposure levels dropped sharply in the early 1980s). Breast cancer did not show any overall excess, although there was an excess in the highest cumulative exposure quartile using a 20 year lag. Internal exposure-response analyses found positive trend for breast cancer using the log of cumulative exposure with a 20 year lag.

CONCLUSIONS

There was little evidence of any excess cancer mortality for the cohort as a whole, with the exception of bone cancer based on small numbers. Positive exposure-response trends for lymphoid tumours were found for males only. Reasons for the sex specificity of this effect are not known. There was also some evidence of a positive exposure-response for breast cancer mortality.

A participatory approach to the study of lifting demands and musculoskeletal symptoms among Hong Kong workers

AIMS

To investigate the use of a worker based methodology to assess the physical stresses of lifting tasks on effort expended, and to associate this loading with musculoskeletal outcomes (MO).

METHODS

A cross sectional study was conducted on 217 male manual handling workers from the Hong Kong area. The effects of four lifting variables (weight of load, horizontal distance, twisting angle, and vertical travel distance) on effort were examined using a linguistic approach (that is, characterising variables in descriptors such as "heavy" for weight of load). The numerical interpretations of linguistic descriptors were established. In addition, the associations between on the job effort and MO were investigated for 10 body regions including the spine, and both upper and lower extremities.

RESULTS

MO were prevalent in multiple body regions (range 12-58%); effort was significantly associated with MO in 8 of 10 body regions (odds ratios with age adjusted ranged from 1.31 for low back to 1.71 for elbows and forearm). The lifting task variables had significant effects on effort, with the weight of load having twice the effect of other variables; each linguistic descriptor was better described by a range of numerical values rather than a single numerical value.

CONCLUSIONS

The participatory worker based approach on musculoskeletal outcomes is a promising methodology. Further testing of this approach is recommended.

Workers' assessments of manual lifting tasks: cognitive strategies and validation with respect to objective indices and musculoskeletal symptoms

OBJECTIVES

To determine the different cognitive strategies adopted by workers in assessing the effects of lifting-task parameters on effort, and to validate workers' assessments.

METHODS

Questionnaires were administered to 217 male workers with varied levels of experience in manual handling. Workers were asked to assess the effects of lifting on perceived effort, using linguistic descriptors (e.g., light, heavy), and to determine the physical meaning of such descriptors. In addition, each worker assessed on-the-job effort, perceived risk of injury and work dissatisfaction, and musculoskeletal outcomes in a cross-sectional design.

RESULTS

Perceived physical effort was significantly associated with lifting variables. Results indicated that the three-cluster strategy is the best performer. Weight of load emerged as the most influential factor that impacted on effort in the most dominant cluster (close to 50% of the observations). The second cluster (25% of the observations) demonstrated that weight, horizontal distance, and twisting angle, contributed equally to effort, and the third cluster had weight and vertical travel distance as the most important variables (with travel distance being more important). Perceived effort was significantly associated with objective indices (i.e., biomechanical lifting equivalent and NIOSH lifting index), and musculoskeletal symptoms in eight body parts.

CONCLUSIONS

Cognitive reasoning of experienced workers may be used as an active device for the evaluation of strenuous physical activities such as lifting tasks. Lifting activities are significantly associated with musculoskeletal symptoms, not only in the lower-back region, but also in seven other body parts; and effort may integrate the effects of both physical (lifting tasks) and non-physical (i.e., work dissatisfaction) factors, as well as perception of risk.

Ethylene oxide and breast cancer incidence in a cohort study of 7576 women (United States)

BACKGROUND

Ethylene oxide (ETO) is a sterilant gas considered to be a human carcinogen, due primarily to excess hematopoietic cancer in exposed cohorts. ETO causes mammary tumors in mice, and has been associated with breast cancer incidence in one small epidemiologic study.

METHODS

We have studied breast cancer incidence in a cohort of 7576 women employed for at least one year and exposed for an average 10.7 years while working in commercial sterilization facilities. Breast cancer incidence (n = 319) was ascertained via interview, death certificates, cancer registries, and medical records. Interviews were obtained for 68% of the cohort.

RESULTS

The standardized incidence ratio (SIR) for incident breast cancer in the whole cohort using external referent rates (SEER) was 0.87 (0.77-0.97). The SIR for those in the top quintile of cumulative exposure, with a 15 year lag, was 1.27 (0.94-1.69), with a positive trend of increasing SIR with increasing exposure (p = 0.002). SIRs are underestimated because breast cancer incidence in the whole cohort was under-ascertained, due to incomplete response and lack of complete coverage by state cancer registries. In internal nested case-control analyses of those with interviews (complete cancer ascertainment), controlling for reproductive risk factors, a positive exposure-response was found with the log of cumulative exposure with a 15-year lag (p = 0.0005). The odds ratio by quintile of cumulative exposure were 1.00 (0 exposure due to 15 year lag), 1.06, 0.99, 1.24, 1.42, and 1.87.

CONCLUSIONS

Our data suggest that ETO is associated with breast cancer, but a causal interpretation is weakened due to some inconsistencies in exposure-response trends and possible biases due to non-response and incomplete cancer ascertainment.

Dioxin: exposure-response analyses and risk assessment

Low-levels of dioxin cause cancer in animals. In 1997 dioxin was found to be a human carcinogen by the International Agency for Research on Cancer, based largely on four studies of industrial workers exposed to high levels. Recently there has been interest in estimating human cancer risk at low level environmental exposures. Here we review quantitative exposure-response analyses and risk assessment for low environmental levels based on the largest existing cohort of workers exposed to dioxin (the U.S. NIOSH cohort). We estimate that doubling background levels of exposure, which may occur for example by eating a lot of fish which have accumulated dioxin, will increase lifetime risk of cancer death by 0.1 to 1.0%. In the US the background risk of cancer death by age 75 is 12%, so doubling background levels of dioxin exposure would increase this lifetime risk to somewhere between 12.1 and 13.0%. Our results agree broadly with results from a German cohort, which is the only other cohort for which a quantitative risk assessment has been conducted.

What is a demanding lifting job for manual handling workers in Hong Kong?

Although lifting tasks are traditionally evaluated by researchers, through the use of methods which depend on one or more approaches (i.e., psychophysical, biomechanical and physiological methods), none of these approaches makes use of expert workers in the evaluation of lifting activities. Given that 97% of lower back symptoms are aches, pains and discomfort and rely on self-reports, it is intuitive to use expert workers in evaluating the stressfulness of lifting activities. In this investigation, 217 workers from three industries in the Hong Kong area were surveyed to determine what constitutes a demanding lifting job from a worker standpoint. This was achieved by asking workers to map, in numerical terms, the level of lifting task parameter described in linguistic values. For example, the weight of load was described in three linguistic descriptors, namely, 'light', 'moderate' and 'heavy'. Then, each worker was asked to assess the meaning of these linguistic descriptors in numerical terms, based on their perception and experience with manual handling work. In this study, workers were asked to map the physical analogue of linguistic descriptors for seven lifting task parameters which are utilized in the NIOSH lifting equation, that is, weight of load, horizontal distance, vertical travel distance, vertical origin of lift, angle of asymmetry, frequency of handling and task duration. The data obtained from the workers were then subjected to validity testing in relation to norms and values reported in the published literature. On a preliminary basis, it appears that workers' assessments are logical and valid. The results suggest that the worker-based methodology is a promising approach and that it is worthwhile to pursue this approach further in the evaluation of industrial lifting activities.

Prevalence of musculoskeletal symptoms in single and multiple body regions and effects of perceived risk of injury among manual handling workers

STUDY DESIGN

A cross-sectional study was conducted to investigate 217 male workers from the Hong Kong with varied levels of manual lifting experience.

OBJECTIVES

To determine whether musculoskeletal symptoms are prevalent in different and multiple body regions among manual handling workers, and to determine whether a simple index (i.e., perceived risk of lifting injury) evaluated by the worker is significantly associated with musculoskeletal outcomes in single and multiple body regions.

SUMMARY OF BACKGROUND DATA

Little research has been conducted to investigate the effect of manual lifting tasks on musculoskeletal symptoms in different and multiple body regions.

METHODS

A structured interview that followed a set of standardized questionnaires was administered to each worker by the same investigator. The workers were asked to detail their demographic characteristics, physical fitness level, years of experience in manual lifting, current working condition, and musculoskeletal symptom survey.

RESULTS

Lower back symptoms were the most frequent among manual handling workers, followed by the shoulders, then the upper back, hips-upper legs, and neck. Finger symptoms had the lowest prevalence values. Musculoskeletal symptoms for multiple body parts (two or more) were more prevalent (64% of all workers) than those for single body regions (19%). Approximately 85% of lower back symptoms were associated with disorders in other body regions. Multivariate analyses indicated that the effects of perceived risk were significant for eight body regions, and that age was significant for three of them. Perceived risk of lifting injury also was significant for multiple body regions.

CONCLUSIONS

Musculoskeletal symptoms are prevalent in single and multiple body regions among manual handling workers. The perceived risk of injury is significantly associated with musculoskeletal symptoms in eight body regions.

Risk assessment for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) based on an epidemiologic study

The International Agency for Research on Cancer (Lyon, France) recently concluded that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is a human carcinogen. There have been few human studies and risk assessments with quantitative exposure data. The authors previously conducted exposure-response analyses based on estimated external TCDD exposure for 3,538 US male chemical workers and found a positive trend for all cancer with increasing cumulative exposure. In the present study, 1988 data from 170 workers with both estimated external exposure and known serum TCDD levels were used to derive the relation between the two. This derived relation was used to estimate serum TCDD levels over time for all 3,538 workers, and new dose-response analyses were conducted by using cumulative serum level. A positive trend (p = 0.003) was found between estimated log cumulative TCDD serum level and cancer mortality. For males, the excess lifetime (75 years) risk of dying of cancer given a TCDD intake of 1.0 pg/kg of body weight per day, twice the background intake, was an estimated 0.05-0.9% above a background lifetime risk of cancer death of 12.4%. Data from this cohort are consistent with another epidemiologic risk assessment from Germany and support recent conclusions by the US Environmental Protection Agency.

Risk assessment for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) based on an epidemiologic study

The International Agency for Research on Cancer (Lyon, France) recently concluded that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is a human carcinogen. There have been few human studies and risk assessments with quantitative exposure data. The authors previously conducted exposure-response analyses based on estimated external TCDD exposure for 3,538 US male chemical workers and found a positive trend for all cancer with increasing cumulative exposure. In the present study, 1988 data from 170 workers with both estimated external exposure and known serum TCDD levels were used to derive the relation between the two. This derived relation was used to estimate serum TCDD levels over time for all 3,538 workers, and new dose-response analyses were conducted by using cumulative serum level. A positive trend (p = 0.003) was found between estimated log cumulative TCDD serum level and cancer mortality. For males, the excess lifetime (75 years) risk of dying of cancer given a TCDD intake of 1.0 pg/kg of body weight per day, twice the background intake, was an estimated 0.05-0.9% above a background lifetime risk of cancer death of 12.4%. Data from this cohort are consistent with another epidemiologic risk assessment from Germany and support recent conclusions by the US Environmental Protection Agency.

Cancer, heart disease, and diabetes in workers exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin

BACKGROUND

In 1997, the International Agency for Research on Cancer classified 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) as a group 1 human carcinogen, based largely on four highly exposed industrial cohorts that showed an excess of all cancers combined. In this study, we extended the follow-up period for the largest of these cohorts by 6 years and developed a job-exposure matrix.

METHODS

We did cohort mortality analyses involving 5132 chemical workers at 12 U.S. plants by use of life table techniques (U.S. population referent) and Cox regression (internal referent). We conducted exposure-response analyses for 69% of the cohort with adequate work history data and adequate plant data on TCDD contamination. All P values are two-sided.

RESULTS

The standardized mortality ratio (SMR) for all cancers combined was 1.13 (95% confidence interval = 1.02-1.25). We found statistically significant positive linear trends in SMRs with increasing exposure for all cancers combined and for lung cancer. The SMR for all cancers combined for the highest exposure group was 1.60 (95% confidence interval = 1.15-1.82). SMRs for heart disease showed a weak increasing trend with higher exposure (P = .14). Diabetes (any mention on the death certificate) showed a negative exposure-response trend. Internal analyses with Cox regression found statistically significant trends for cancer (15-year lag time) and heart disease (no lag).

CONCLUSIONS

Our analyses suggest that high TCDD exposure results in an excess of all cancers combined, without any marked specificity. However, excess cancer was limited to the highest exposed workers, with exposures that were likely to have been 100-1000 times higher than those experienced by the general population and similar to the TCDD levels used in animal studies.

Evaluation of diabetes mellitus, serum glucose, and thyroid function among United States workers exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin

OBJECTIVE

Some studies suggest that exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) may affect glucose metabolism and thyroid function. To further assess the relation between exposure to TCDD and endocrine function, data from the largest morbidity study of industrial workers exposed to TCDD were examined.

METHODS

A cross sectional study of workers employed > 15 years earlier in the manufacture of 2,4,5-trichlorophenol or one of its derivatives at two United States chemical plants was conducted. The referent group consisted of people with no occupational exposure to phenoxy herbicides and were recruited from the neighbourhoods where the workers lived.

RESULTS

A total of 281 workers and 260 unexposed referents participated. The mean current serum lipid adjusted TCDD concentration among workers was 220 pg/g lipid, and among referents was 7 pg/g lipid (p < 0.05). The half life extrapolated TCDD concentrations (the estimated TCDD concentration when occupational exposure to TCDD stopped) among workers averaged 1900 pg/g lipid (range: not detected--30,000 pg/g lipid). Overall, the prevalence of diabetes mellitus was not significantly different between the workers and referents. Also, there was not a significant positive trend between prevalence of diabetes and increasing serum TCDD concentration. However, diabetes was found in six of 10 (60%) workers with current serum TCDD concentrations > 1500 pg/g lipid. After excluding subjects being treated for diabetes, workers in the group with the highest half life extrapolated TCDD concentrations had a significantly increased adjusted mean serum glucose concentration compared with referents (p = 0.03). Workers were also found to have a significantly higher adjusted mean free thyroxine index compared with referents (p = 0.02), especially among workers in the group with the highest half life extrapolated TCDD concentrations. However, no evidence was found that workers exposed to TCDD were at increased risk of thyroid disease.

CONCLUSIONS

These findings provide modest evidence that exposure to TCDD may affect thyroid function and glucose metabolism.

Effect of age and height on vibrotactile threshold among 1,663 U.S. workers

Assessment of vibrotactile threshold has gained application in studies of neuropathies induced by toxic substances, compression, and vibration. The effect of age and height on vibrotactile threshold is of interest for its own sake and for the purpose of confounder control. We have studied the relation between finger and toe vibrotactile thresholds and age and height in five studies carried out by the National Institute for Occupational Safety and Health with vibrometry data (N = 1,663). A unique property of the merged data set was its wide age range from 14 to 82 years (mean 42 years). We demonstrate a J-shaped increase in finger threshold value (expressed on a log scale) with age, with no increase up to age 35 and a linear increase thereafter. For finger threshold, height was not an important predictor. The data were sparser (n = 541) for toe threshold but suggested a linear increase with both age and height. While consistent with prior data, this study provides a better understanding of the relation between vibrotactile threshold and age and height than has been available before. The greater effect of age and height on toe rather than finger threshold is consistent with the hypothesis that the length of the nerve increases susceptibility to peripheral neuropathy.

Diesel exhaust and lung cancer in the trucking industry: exposure-response analyses and risk assessment

BACKGROUND

Diesel exhaust is considered a probable human carcinogen by the International Agency for Research on Cancer (IARC). The epidemiologic evidence rests on studies of lung cancer among truck drivers, bus drivers, shipyard workers, and railroad workers. The general public is exposed to diesel exhaust in ambient air. Two regulatory agencies are now considering regulating levels of diesel exhaust: the California EPA (ambient levels) and the Mine Safety Health Administration (MSHA) (occupational levels). To date, there have been few quantitative exposure-response analyses of diesel and lung cancer based on human data.

METHODS

We conducted exposure-response analyses among workers in the trucking industry, adjusted for smoking. Diesel exhaust exposure was estimated based on a 1990 industrial hygiene survey. Past exposures were estimated assuming that they were a function of 1) the number of heavy duty trucks on the road, 2) the particulate emissions (grams/mile) of diesel engines over time, and 3) leaks from trucks' exhaust systems for long-haul drivers.

RESULTS

Regardless of assumptions about past exposure, all analyses resulted in significant positive trends in lung cancer risk with increasing cumulative exposure. A male truck driver exposed to 5 micrograms/m3 of elemental carbon (a typical exposure in 1990, approximately five times urban background levels) would have a lifetime excess risk of lung cancer of 1-2% above a background risk of 5%.

CONCLUSIONS

We found a lifetime excess risk ten times higher than the 1 per 1,000 excess risk allowed by OSHA in setting regulations. There are about 2.8 million truck drivers in the U.S. Our results depend on estimates about unknown past exposures, and should be viewed as exploratory. They conform reasonably well to recent estimates for diesel-exposed railroad workers done by the California EPA, although those results themselves have been disputed.

Prevalence proportion ratios: estimation and hypothesis testing

BACKGROUND

Recent communications have argued that often it may not be appropriate to analyse cross-sectional studies of prevalent outcomes with logistic regression models. The purpose of this communication is to compare three methods that have been proposed for application to cross sectional studies: (1) a multiplicative generalized linear model, which we will call the log-binomial model, (2) a method based on logistic regression and robust estimation of standard errors, which we will call the GEE-logistic model, and (3) a Cox regression model.

METHODS

Five sets of simulations representing fourteen separate simulation conditions were used to test the performance of the methods.

RESULTS

All three models produced point estimates close to the true parameter, i.e. the estimators of the parameter associated with exposure had negligible bias. The Cox regression produced standard errors that were too large, especially when the prevalence of the disease was high, whereas the log-binomial model and the GEE-logistic model had the correct type I error probabilities. It was shown by example that the GEE-logistic model could produce prevalences greater than one, whereas it was proven that this could not happen with the log-binomial model. The log-binomial model should be preferred.

Stressors and adverse outcomes for female construction workers

The authors examined the impact of a number of job stressors, including sexual harassment and gender-based discrimination, on female construction workers' level of job satisfaction and psychological and physical health. Results from a telephone survey with 211 female laborers indicated that having responsibility for others' safety and having support from supervisors and male coworkers was related to greater job satisfaction. Increased reported psychological symptoms were also related to increased responsibility, as well as skill underutilization, experiencing sexual harassment and gender-based discrimination from supervisors and coworkers, and having to overcompensate at work. Perceptions of overcompensation at work and job uncertainty were positively associated with self-reports of insomnia. Finally, sexual harassment and gender discrimination were positively related to reports of increased nausea and headaches.

Thyroid hormones and cytogenetic outcomes in backpack sprayers using ethylenebis(dithiocarbamate) (EBDC) fungicides in Mexico

Ethylenebis(dithiocarbamate) (EBDC) fungicides are used heavily in the United States. EBDCs (e.g., mancozeb, maneb) are metabolized to ethylene thiourea (ETU). The EPA classifies ETU as a carcinogen, based on thyroid and other cancers in rodents, and has restricted the use of EBDCs, while requiring workers to use protective equipment. There are no data on the potential carcinogenicity of EBDCs in humans, and there is only one study on human genotoxicity. ETU is known to cause decreases of thyroxine (T4) and increases in thyroid-stimulating hormone (TSH) in rodents. We have studied cytogenetic outcomes and serum thyroid hormone levels among 49 heavily exposed workers without protective equipment spraying EBDC on tomatoes in Mexico. We also studied 14 lightly exposed landowners and 31 nonexposed controls. Urinary ETU was used to compare exposure between groups. We found an increase in TSH (p = 0.05) among applicators compared to controls, but no decrease in thyroid hormone (T4). We found increases in sister chromatid exchange (p = 0.03) and in chromosome translocations (chromosome aberrations that persist through cell division) for applicators compared to controls (p = 0.05). However, the subset of reciprocal translocations showed a lesser increase (p = 0.24). Our data suggest that EBDCs affect the thyroid gland and the lymphocyte genome among heavily exposed workers. However, our data are limited to subclinical outcomes, are of borderline statistical significance, and should be interpreted with caution.

Epidemiologic study of Down syndrome in a racially diverse California population, 1989-1991

The prevalence of Down syndrome was studied among all live births occurring between 1989 and 1991 in the California counties monitored by the California Birth Defects Monitoring Program. Objectives of this study were: 1) to calculate adjusted prevalence rates and quinquennial maternal age-specific risk rates of Down syndrome after adjusting for elective abortion of prenatally diagnosed fetuses; 2) to estimate the impact of prenatal diagnosis and subsequent elective abortion of affected fetuses on the observed prevalence of Down syndrome; and 3) to examine sex ratios among liveborn infants and fetuses with Down syndrome. The racial/ethnic diversity and large size of the population allowed the data to be stratified into five racial categories-Hispanics, whites, Asians, blacks, and others. For the period 1989-1991, the observed prevalence of Down syndrome was 1.13 per 1,000 live births, and the adjusted total prevalence, which took into account the termination of affected pregnancies following prenatal diagnosis, was 1.53 per 1,000 live births. In a comparison of quinquennial maternal age-specific risk rates of Down syndrome by race, Hispanics and whites were the only groups with rates that differed significantly from each other, with Hispanics exhibiting higher rates at maternal ages under 40 years. The overall reduction in live births with Down syndrome in 1989-1991 that could be attributed to prenatal diagnosis and elective abortion of affected fetuses was 25.8%, with a 49.1% reduction being observed at maternal ages > or = 35 years. In 1990-1991, Hispanics had the lowest overall reduction (10.0%), while whites had the highest reduction (46.3%). The male: female ratios among liveborns with Down syndrome were significantly higher than those among all live births, and race had a significant association with sex ratios in both cases and controls. These findings indicate that prenatal diagnosis and elective termination of affected pregnancies has had a substantial impact in reducing the number of liveborns with Down syndrome in the monitored California counties. The effect was greatest for whites and least for Hispanics, with results indicating considerable variation in the use of prenatal diagnostic services among racial/ethnic groups. Estimates of adjusted total prevalence and reduction in live births with Down syndrome in this study should be considered minimal because of some underascertainment of prenatally diagnosed cases.

Negative bias in exposure-response trends in occupational studies: modeling the healthy workers survivor effect

Many occupational studies analyze trends between cumulative exposure and mortality. The authors show that such trends are, in general, negatively confounded by employment status. Mortality rates for workers who leave work ("inactive" workers) are higher than for active workers because some workers leave because they are ill. The percentage of inactive relative to active person-time is higher in low categories of cumulative exposure, causing employment status to act as a negative confounder of exposure-response trends (the opposite occurs for time-since-hire). We illustrate these phenomena using 10 "negative" mortality studies, in which adjustment for employment status removes false trends. However, adjustment for employment status will lead to biased estimates when it acts as an intermediate variable between cumulative exposure and death, as occurs directly when exposure causes a disabling disease that, in turn, causes death or indirectly when exposure causes workers to leave work. The authors illustrate this problem using simulated follow-up data for leaving, disease incidence, and mortality. In the null case in which cumulative exposure affects neither disease incidence (or mortality) nor leaving rates, employment status indeed acts as a negative confounder of exposure-response trends, and traditional adjustment eliminates this confounding. However, when cumulative exposure affects disease incidence or rates of leaving, adjustment for employment status will not be adequate. Employment status falls under the general rubric of variables that are simultaneously confounders and intermediate variables.

Modifiers of exposure-response estimates for lung cancer among miners exposed to radon progeny

The association between lung cancer and exposure to radon decay products has been well established. Despite agreement on this point, there is still some degree of uncertainty regarding characteristics of the exposure-response relationship. The use of studies of underground miners to estimate lung cancer risks due to residential radon exposure depends upon a better understanding of factors potentially modifying the exposure-response relationship. Given the diversity in study populations regarding smoking status, mining conditions, risk analysis methodology, and referent populations, the risk estimates across studies are quite similar. However, several factors partially contributing to differences in risk estimates are modified by attained age, time since last exposure, exposure rate, and cigarette smoking patterns. There is growing agreement across studies that relative risk decreases with attained age and time since last exposure. Several studies have also found an inverse exposure-rate effect, i.e., low exposure rates for protracted duration of exposure are more hazardous than equivalent cumulative exposures received at higher rates for shorter periods of time. Additionally, the interaction between radon exposure and cigarette smoking appears to be intermediate between additive and multiplicative in a growing number of studies. Quantitative estimates of these modifying factors are given using a new analysis of data from the latest update of the Colorado Plateau uranium miners cohort.

Determinants of emergency psychiatric admission for adolescents and adults

The authors compared correlates of admission for 100 patients older than 18 years and 100 patients younger than 18 evaluated in a psychiatric emergency service. Stepwise linear logistic regression analysis identified a combination of variables that best predicted the odds of hospitalization for each group. For adolescents, these variables, in order of importance, were suicidal tendencies, physical abuse, a primary diagnosis of schizophrenia, age, and number of suicide attempts. For adults, the variables were delusions, aggressive behavior, suicidal tendencies, and a primary diagnosis of schizophrenia or affective disorder. The authors discuss the implications of these findings for acute psychiatric treatment of adolescents.

A low protein-high linoleate diet increases glomerular PGE2 and protects renal function in rats with reduced renal mass

Renal function deteriorates progressively in partially nephrectomized rats. This deterioration of renal function may be ameliorated by a diet either low in protein or high in linoleic acid. In the present experiment, partially nephrectomized rats were pair fed diets low in protein, high in linoleic acid or both low in protein and high in linoleic acid. Survival of renal function was most prolonged in rats fed a diet with both a low protein and high linoleic acid content; glomeruli from these animals demonstrated increased glomerular PGE2 production. This additive effect may be mediated by increased production of the vasodilatory PGE2 by glomeruli.

Dietary fat in experimental nephrotic syndrome: beneficial effects of fish oil on serum lipids and, indirectly, on the kidney

Three isocaloric diets with different fat composition were fed to rats for seven weeks after the production of nephrotic syndrome by adriamycin. The effects of feeding 3% and 14% fish oil were compared with those of feeding beef fat. At the fourth week of feeding the levels of triglycerides and cholesterol were lower in both fish oil fed groups. At the seventh week these levels, and the LDL cholesterol, were lower only in the 14% fish oil group. In rats fed beef fat, but not in those fed fish oil, there was a striking positive correlation of the four-week serum triglycerides and cholesterol with the seven-week serum creatinine level and with the degree of glomerular hyalinosis and endothelial swelling. The favorable effects of fish oil feeding on serum lipids may have a protective effect on the development of glomerular damage.