Guidelines to evaluate human observational studies for quantitative risk assessment

Occupational exposure to endotoxins and small cell lung cancer: a systematic review with meta-analysis

The relationship of occupational exposure to endotoxins with different histologic subtypes of lung cancer has not been established. Our objective was to conduct a systematic review with meta-analysis to assess the effect of exposure to endotoxins on the development of small cell lung cancer (SCLC). A bibliographic search was conducted using MEDLINE, Embase, CENTRAL, and Web of Science databases until December 2022, including all cohort and/or case-control studies that examined occupational exposure to endotoxins and SCLC. Risk of bias was assessed using the U.S. Office of Health Assessment and Translation tool. A random effects model was applied, publication bias were assessed, and a sensitivity analysis was conducted. Four papers were selected for meta-analysis purposes. A total of 144 incident cases of SCLC and 897 population or hospital controls were included. Occupational exposure to endotoxins was considered for textile/leather industry and agricultural sector workers exposed to endotoxins originating from wool, cotton, or leather dust. Except for one study, all investigations were classified as having a low probability of risk of biases. The results of the meta-analysis were not statistically significant (pooled OR: 0.86; 95% CI:0.69-1.08). In addition, neither between-study heterogeneity (I2=0%;p=0.92) nor publication bias was observed (p=0.49). The results of the sensitivity analysis, after including five studies that assessed the risk of SCLC among textile industry and crop/livestock farm workers (not specifically exposed to endotoxins), showed a negative statistically non-significant association and low between-study heterogeneity (pooled OR: 0.90; 95% CI:0.79-1.02; I2=22%;p=0.23). Subjects exposed to occupational exposure to endotoxins seem to exhibit a negative association with the development of SCLC, although the results are not conclusive.

Water, Water Everywhere, but Every Drop Unique: Challenges in the Science to Understand the Role of Contaminants of Emerging Concern in the Management of Drinking Water Supplies

The protection and management of water resources continues to be challenged by multiple and ongoing factors such as shifts in demographic, social, economic, and public health requirements. Physical limitations placed on access to potable supplies include natural and human-caused factors such as aquifer depletion, aging infrastructure, saltwater intrusion, floods, and drought. These factors, although varying in magnitude, spatial extent, and timing, can exacerbate the potential for contaminants of concern (CECs) to be present in sources of drinking water, infrastructure, premise plumbing and associated tap water. This monograph examines how current and emerging scientific efforts and technologies increase our understanding of the range of CECs and drinking water issues facing current and future populations. It is not intended to be read in one sitting, but is instead a starting point for scientists wanting to learn more about the issues surrounding CECs. This text discusses the topical evolution CECs over time (Section 1), improvements in measuring chemical and microbial CECs, through both analysis of concentration and toxicity (Section 2) and modeling CEC exposure and fate (Section 3), forms of treatment effective at removing chemical and microbial CECs (Section 4), and potential for human health impacts from exposure to CECs (Section 5). The paper concludes with how changes to water quantity, both scarcity and surpluses, could affect water quality (Section 6). Taken together, these sections document the past 25 years of CEC research and the regulatory response to these contaminants, the current work to identify and monitor CECs and mitigate exposure, and the challenges facing the future.

Key event-informed risk models for benzene-induced acute myeloid leukaemia

Occupational exposure to benzene at levels of 10 ppm or more has been associated with increased risk of acute myeloid leukaemia (AML). The mode of action (MOA) for AML development leading to mortality is anticipated to include multiple earlier key events, which can be observed in hematotoxicity and genetic toxicity in peripheral blood of exposed workers. Prevention of these early events would lead to prevention of the apical, adverse outcomes, the morbidity and mortality caused by the myelodysplastic syndromes (MDS) and AML. Incorporation of key event information should modify the risk model, but few modification approaches have been suggested. To that end, two approaches to risk model modification are described that use sub-linear and segmented linear increases in risk below key events, while maintaining a linear increase in AML mortality risk beginning at 2 ppm, the lowest observed adverse effect concentration (LOAEC) identified for hemato- and geno- toxicity in high quality studies of human occupational exposure. Below 2 ppm two different modification approaches to quantitative risk models were applied: a continuously decreasing slope model and a segmented modification in slope. These two approaches provide greater flexibility to incorporate MOA information in risk model development and selection.

Derivation of an occupational exposure limit for benzene using epidemiological study quality assessment tools

This paper derives an occupational exposure limit for benzene using quality assessed data. Seventy-seven genotoxicity and 36 haematotoxicity studies in workers were scored for study quality with an adapted tool based on that of Vlaanderen et al., 2008 (Environ Health. Perspect. 116 1700-5). These endpoints were selected as they are the most sensitive and relevant to the proposed mode of action (MOA) and protecting against these will protect against benzene carcinogenicity. Lowest and No- Adverse Effect Concentrations (LOAECs and NOAECs) were derived from the highest quality studies (i.e. those ranked in the top tertile or top half) and further assessed as being "more certain" or "less certain". Several sensitivity analyses were conducted to assess whether alternative "high quality" constructs affected conclusions. The lowest haematotoxicity LOAECs showed effects near 2 ppm (8 h TWA), and no effects at 0.59 ppm. For genotoxicity, studies also showed effects near 2 ppm and showed no effects at about 0.69 ppm. Several sensitivity analyses supported these observations. These data define a benzene LOAEC of 2 ppm (8 h TWA) and a NOAEC of 0.5 ppm (8 h TWA). Allowing for possible subclinical effects in bone marrow not apparent in studies of peripheral blood endpoints, an OEL of 0.25 ppm (8 h TWA) is proposed.

Estimated burden of disease from arsenic in drinking water supplied by domestic wells in the United States

Well water around the world can be contaminated with arsenic, a naturally occurring geological element that has been associated with myriad adverse health effects. Persons obtaining their drinking water from private wells are often responsible for well testing and water treatment. High levels of arsenic have been reported in well water-supplied areas of the United States. We quantified - in cases and dollars - the potential burden of disease associated with the ingestion of arsenic through private well drinking water supplies in the United States. To estimate cancer and cardiovascular disease burden, we developed a Monte Carlo model integrating three input streams: (1) regional concentrations of arsenic in drinking water wells across the United States; (2) dose-response relationships in the form of cancer slope factors and hazard ratios; and (3) economic cost estimates developed for morbidity endpoints using 'cost-of-illness' methods and for mortality using 'value per statistical life' estimates. Exposure to arsenic in drinking water from U.S. domestic wells is modeled to contribute 500 annual premature deaths from ischemic heart disease and 1,000 annual cancer cases (half of them fatal), monetized at $10.9 billion (2017 USD) annually. These considerable public health burden estimates can be compared with the burdens of other priority public health issues to assist in decision-making.

Estimation of the Leukemia Risk in Human Populations Exposed to Benzene from Tobacco Smoke Using Epidemiological Data

Several epidemiological studies have demonstrated an association between occupational benzene exposure and increased leukemia risk, in particular acute myeloid leukemia (AML). However, there is still uncertainty as to the risk to the general population from exposure to lower environmental levels of benzene. To estimate the excess risk of leukemia from low-dose benzene exposure, various methods for incorporating epidemiological data in quantitative risk assessment were utilized. Tobacco smoke was identified as one of the main potential sources of benzene exposure and was the focus of this exposure assessment, allowing further investigation of the role of benzene in smoking-induced leukemia. Potency estimates for benzene were generated from individual occupational studies and meta-analysis data, and an exposure assessment for two smoking subgroups (light and heavy smokers) carried out. Subsequently, various techniques, including life-table analysis, were then used to evaluate both the excess lifetime risk and the contribution of benzene to smoking-induced leukemia and AML. The excess lifetime risk for smokers was estimated at between two and six additional leukemia deaths in 10,000 and one to three additional AML deaths in 10,000. The contribution of benzene to smoking-induced leukemia was estimated at between 9% and 24% (Upper CL 14-31%). For AML this contribution was estimated as 11-30% (Upper CL 22-60%). From the assessments carried out here, it appears there is an increased risk of leukemia from low-level exposure to benzene and that benzene may contribute up to a third of smoking-induced leukemia. Comparable results from using methods with varying degrees of complexity were generated.

Low-level arsenic exposure and developmental neurotoxicity in children: A systematic review and risk assessment

Risk assessments of arsenic have focused on skin, bladder, and lung cancers and skin lesions as the sensitive cancer and non-cancer health endpoints, respectively; however, an increasing number of epidemiologic studies that can inform risk assessment have examined neurodevelopmental effects in children. We conducted a systematic review and risk assessment based on the epidemiologic literature on possible neurodevelopmental effects at lower arsenic exposures. Twenty-four cross-sectional, case-control, and cohort studies were identified that report on the association between low-level arsenic exposure (i.e., largely <100 μg/L of arsenic in drinking water) and neurological outcomes in children. Although the overall evidence does not consistently show a causal dose-response relationship at low doses, the most rigorously conducted studies from Bangladesh indicate possible inverse associations with cognitive function, predominantly involving concurrent arsenic exposure as measured by biomarkers (i.e., arsenic in urine or blood) and raw verbal test scores at ages 5-11 years. Issues such as non-comparability of outcome measures across studies; inaccuracies of biomarkers and other measures of inorganic arsenic exposure; potential effect modification by cultural practices; insufficient adjustment for nutritional deficiencies, maternal IQ, and other important confounders; and presence of other neurotoxicants in foreign populations limit generalizability to U.S.

POPULATIONS

Of the few U.S. studies available, the most rigorously conducted study did not find a consistent dose-response relationship between arsenic concentrations in tap water or toenails and decrements in IQ scores. Assuming that the strongest dose-response relationship from the most rigorous evidence from Bangladesh is generalizable to U.S. populations, possible reference doses were estimated in the range of 0.0004-0.001 mg/kg-day. These doses are higher than the U.S. Environmental Protection Agency reference dose for chronic lifetime exposure, thus indicating protectiveness of the existing value for potential neurotoxicity in children. This reference dose is undergoing revision as EPA considers various health endpoints in the reassessment of inorganic arsenic health risks.

Bias and power in group-based epidemiologic studies of low-back pain exposure and outcome--effects of study size and exposure measurement efforts

OBJECTIVES

Exposure-outcome studies, for instance on work-related low-back pain (LBP), often classify workers into groups for which exposures are estimated from measurements on a sample of workers within or outside the specific study. The present study investigated the influence on bias and power in exposure-outcome associations of the sizes of the total study population and the sample used to estimate exposures.

METHODS

At baseline, lifting, trunk flexion, and trunk rotation were observed for 371 of 1131 workers allocated to 19 a-priori defined occupational groups. LBP (dichotomous) was reported by all workers during 3 years of follow-up. All three exposures were associated with LBP in this parent study (P < 0.01). All 21 combinations of n = 10, 20, 30 workers per group with an outcome, and k = 1, 2, 3, 5, 10, 15, 20 workers actually being observed were investigated using bootstrapping, repeating each combination 10000 times. Odds ratios (OR) with P values were determined for each of these virtual studies. Average OR and statistical power (P < 0.05 and P < 0.01) was determined from the bootstrap distributions at each (n, k) combination.

RESULTS

For lifting and flexed trunk, studies including n ≥ 20 workers, with k ≥ 5 observed, led to an almost unbiased OR and a power >0.80 (P level = 0.05). A similar performance required n ≥ 30 workers for rotated trunk. Small numbers of observed workers (k) resulted in biased OR, while power was, in general, more sensitive to the total number of workers (n).

CONCLUSIONS

In epidemiologic studies using a group-based exposure assessment strategy, statistical performance may be sufficient if outcome is obtained from a reasonably large number of workers, even if exposure is estimated from only few workers per group.

A comparison of posterior lumbar interbody fusion and transforaminal lumbar interbody fusion: a literature review and meta-analysis

Background

We compared the perioperative results and complications associated with PLIF and TLIF, and collected evidence for choosing the better fusion method.

Methods

A literature survey of the MEDLINE and EMBASE databases identified 7 comparative observational studies that met our inclusion criteria. Checklists by Cowley were used to evaluate the risk of bias of the included studies. A database including patient demographic information, perioperative results, and complications was established. The summary odds ratio and weighed mean difference with 95% confidence interval were calculated with a random-effects model.

Results

We found that PLIF had a higher complication rate (P <0.00001), and TLIF reduced the rate of durotomy (P = 0.01). No statistical difference was found between the two groups with regard to clinical satisfaction (P = 0.54), blood loss (P = 0.14), vertebral root injury (P = 0.08), graft malposition (P = 0.06), infection (P = 0.36), or rate of radiographic fusion (P = 0.27). The evidence indicated that PLIF required longer operative time (P = 0.03).

Conclusions

The evidence indicated that TLIF could reduce the complication rate and durotomy. Neither TLIP nor PLIF was found superior in terms of clinical satisfaction or radiographic fusion rate. PLIF might result in longer time in surgery.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2474-15-367) contains supplementary material, which is available to authorized users.

Evaluating uncertainty to strengthen epidemiologic data for use in human health risk assessments

BACKGROUND

There is a recognized need to improve the application of epidemiologic data in human health risk assessment especially for understanding and characterizing risks from environmental and occupational exposures. Although there is uncertainty associated with the results of most epidemiologic studies, techniques exist to characterize uncertainty that can be applied to improve weight-of-evidence evaluations and risk characterization efforts.

METHODS

This report derives from a Health and Environmental Sciences Institute (HESI) workshop held in Research Triangle Park, North Carolina, to discuss the utility of using epidemiologic data in risk assessments, including the use of advanced analytic methods to address sources of uncertainty. Epidemiologists, toxicologists, and risk assessors from academia, government, and industry convened to discuss uncertainty, exposure assessment, and application of analytic methods to address these challenges.

SYNTHESIS

Several recommendations emerged to help improve the utility of epidemiologic data in risk assessment. For example, improved characterization of uncertainty is needed to allow risk assessors to quantitatively assess potential sources of bias. Data are needed to facilitate this quantitative analysis, and interdisciplinary approaches will help ensure that sufficient information is collected for a thorough uncertainty evaluation. Advanced analytic methods and tools such as directed acyclic graphs (DAGs) and Bayesian statistical techniques can provide important insights and support interpretation of epidemiologic data.

CONCLUSIONS

The discussions and recommendations from this workshop demonstrate that there are practical steps that the scientific community can adopt to strengthen epidemiologic data for decision making.

What is the optimum fusion technique for adult spondylolisthesis-PLIF or PLF or PLIF plus PLF? A meta-analysis from 17 comparative studies

STUDY DESIGN

A meta-analysis and systemic review.

OBJECTIVE

To pool scientific evidence for the optimum selection in the treatment of lumbar spondylolisthesis by comparing the clinical effect of posterolateral fusion (PLF), posterior lumbar interbody fusion (PLIF), and PLIF plus PLF.

SUMMARY OF BACKGROUND DATA

Clinical effect of the 3 fusion techniques has been reported in many studies. However, which is the best method is in dispute.

METHODS

A systematic search was conducted in MEDLINE, EMBASE, and the Cochrane Collaboration Library from January 1950 through May 2013. Comparative studies were performed according to eligibility criteria. Weighted mean differences and risk differences were calculated for common outcomes. The final strength of evidence was expressed as different level recommended by the Grading of Recommendations Assessment, Development, and Evaluation Working Group.

RESULTS

Four randomized controlled trials and 13 observational studies were eligible. PLIF was more effective than PLF in the improvement of clinical satisfaction (odds ratio [OR], 0.52; 95% confidence interval (CI), 0.31-0.89; P=0.02). No significant differences in the primary outcomes were seen between PLIF plus PLF and PLF (OR, 0.88; 95% CI, 0.47-1.64; P=0.69). For the complication rate, the differences were not significant between PLIF and PLF, and between PLIF plus PLF and PLF (OR, 2.27; 95% CI, 0.95-5.42; P=0.07; OR, 0.74; 95% CI, 0.22-2.44; P=0.62, respectively). In the secondary outcomes, PLIF was more effective than PLF in the improvement of fusion rate (P=0.0007) and reoperation rate (P=0.004). However, PLIF plus PLF failed to reveal more superiority than PLF (P>0.05).

CONCLUSION

PLIF plus PLF did not show more superiority than PLF alone. PLIF alone improved clinical satisfaction and decreased complication rate compared with PLF. PLIF maybe be better than the other 2 fusion methods in the treatment of lumbar spondylolisthesis. However, conclusions need to be treated with caution because of lack of high quality of evidence.

LEVEL OF EVIDENCE

1.

Tetrachloroethylene exposure and bladder cancer risk: a meta-analysis of dry-cleaning-worker studies

BACKGROUND

In 2012, the International Agency for Research on Cancer classified tetrachloroethylene, used in the production of chemicals and the primary solvent used in dry cleaning, as "probably carcinogenic to humans" based on limited evidence of an increased risk of bladder cancer in dry cleaners.

OBJECTIVES

We assessed the epidemiological evidence for the association between tetrachloroethylene exposure and bladder cancer from published studies estimating occupational exposure to tetrachloroethylene or in workers in the dry-cleaning industry.

METHODS

Random-effects meta-analyses were carried out separately for occupational exposure to tetrachloroethylene and employment as a dry cleaner. We qualitatively summarized exposure-response data because of the limited number of studies available.

RESULTS

The meta-relative risk (mRR) among tetrachloroethylene-exposed workers was 1.08 (95% CI: 0.82, 1.42; three studies; 463 exposed cases). For employment as a dry cleaner, the overall mRR was 1.47 (95% CI: 1.16, 1.85; seven studies; 139 exposed cases), and for smoking-adjusted studies, the mRR was 1.50 (95% CI: 0.80, 2.84; 4 case-control studies).

CONCLUSIONS

Our meta-analysis demonstrates an increased risk of bladder cancer in dry cleaners, reported in both cohort and case-control studies, and some evidence for an exposure-response relationship. Although dry cleaners incur mixed exposures, tetrachloroethylene could be responsible for the excess risk of bladder cancer because it is the primary solvent used and it is the only chemical commonly used by dry cleaners that is currently identified as a potential bladder carcinogen. Relatively crude approaches in exposure assessment in the studies of "tetrachloroethylene-exposed workers" may have attenuated the relative risks.

Association of low-level arsenic exposure in drinking water with cardiovascular disease: a systematic review and risk assessment

The U.S. Environmental Protection Agency (EPA) is developing an integrated assessment of non-cancer and cancer risk assessment of inorganic arsenic (iAs). Cardiovascular disease (CVD) in association with iAs exposure has been examined in a number of studies and provides a basis for evaluating a reference dose (RfD) for assessing potential non-cancer health risks of arsenic exposure. In this systematic review of low-level iAs exposure (i.e., <100-150μg/L arsenic water concentration) and CVD in human populations, 13 cohort and case-control studies from the United States, Taiwan, Bangladesh, and China were identified and critically examined for evidence for derivation of a RfD. Eight cross-sectional and ecological studies from the United States were also examined for additional information. Prospective cohort data from Bangladesh provided the strongest evidence for determining the point of departure in establishing a candidate RfD based on a combined endpoint of mortality from "ischemic heart disease and other heart diseases." This study as well as the overall literature supported a no-observed-adverse-effect level of 100μg/L for arsenic in water, which was equivalent to an iAs dose of 0.009mg/kg-day (based on population-specific water consumption rates and dietary iAs intake). The study population was likely sensitive to arsenic toxicity because of nutritional deficiencies affecting arsenic methylation and one-carbon metabolism, as well as increasing CVD risk. Evidence is less clear on the interaction of CVD risk factors in the United States (e.g., diabetes, obesity, and hypertension) with arsenic at low doses. Potential uncertainty factors up to 3 resulted in a RfD for CVD in the range of 0.003-0.009mg/kg-day. Although caution should be exercised in extrapolating these results to the U.S. general population, these doses allow a margin of exposure that is 10-30 times the current RfD derived by EPA (based on skin lesions in Southwest Taiwan). These findings suggest that the current EPA RfD is protective of CVD.

A survey of frameworks for best practices in weight-of-evidence analyses

The National Academy of Sciences (NAS) Review of the Environmental Protection Agency's Draft IRIS Assessment of Formaldehyde proposed a "roadmap" for reform and improvement of the Agency's risk assessment process. Specifically, it called for development of a transparent and defensible methodology for weight-of-evidence (WoE) assessments. To facilitate development of an improved process, we developed a white paper that reviewed approximately 50 existing WoE frameworks, seeking insights from their variations and nominating best practices for WoE analyses of causation of chemical risks. Four phases of WoE analysis were identified and evaluated in each framework: (1) defining the causal question and developing criteria for study selection, (2) developing and applying criteria for review of individual studies, (3) evaluating and integrating evidence and (4) drawing conclusions based on inferences. We circulated the draft white paper to stakeholders and then held a facilitated, multi-disciplinary invited stakeholder workshop to broaden and deepen the discussion on methods, rationales, utility and limitations among the surveyed WoE frameworks. The workshop developed recommendations for improving the conduct of WoE evaluations. Based on the analysis of the 50 frameworks and discussions at the workshop, best practices in conducting WoE analyses were identified for each of the four phases. Many of these best practices noted from the analysis and workshop could be implemented immediately, while others may require additional refinement as part of the ongoing discussions for improving the scientific basis of chemical risk assessments.

Cardiovascular aspects of psoriasis: an updated review

Psoriasis, a systemic inflammatory disease, is associated with enhanced atherosclerosis and risk of cardiovascular (CV) disease, which may account for higher morbidity and mortality rates in psoriatic patients. It especially applies to younger psoriatic patients with more severe disease, reducing their life expectancy. The aim of the study was to review the literature on CV disease in psoriasis as well as the pathogenic mechanisms shared between psoriasis and atherosclerosis. Moreover, case-control and cohort studies published between 2006 and 2011 were selected for meta-analysis. The meta-analysis indicates elevated risk of cardiovascular events in psoriatic patients in relation to non-psoriatic controls (OR 1.28; 95% CI 1.18-1.38). It is suggested that the treatment of the inflammatory processes involved in the pathogenesis of both psoriasis and atherosclerosis may be beneficial in reducing the CV risk in psoriatic patients. Further in-depth investigations, including prospective studies, are needed to enable more effective management of psoriatic patients in the future.

A systematic review with meta-analysis of posterior interbody fusion versus posterolateral fusion in lumbar spondylolisthesis

PURPOSE

To compare the clinical effectiveness of posterior lumbar interbody fusion (PLIF) and posterolateral fusion (PLF) for lumbar spondylolisthesis and to collect scientific evidence for determining which fusion method is better.

METHODS

After systematic search, comparative studies were selected according to eligibility criteria. Checklists by Furlan and by Cowley were used to evaluate the risk of bias of the included randomized controlled trials (RCTs) and nonrandomized controlled studies, respectively. Weighed mean differences (WMDs) and risk differences were calculated for common outcomes. The final strength of evidence was expressed as different levels recommended by the GRADE Working Group.

RESULTS

Four RCTs and five comparative observational studies were identified. Moderate-quality evidence indicated that PLIF was more effective than PLF for clinical satisfaction [odds ratios (OR) 0.49, 95 % confidence limits (95 % CI): (0.28, 0.88, P = 0.02)]. Moderate-quality evidence showed that no significant difference was found for the complication rate [OR 2.28, 95 % CI (0.97, 5.35), P = 0.06]. In secondary outcomes, moderate-quality evidence indicated that PLIF improved fusion rate [OR 0.32, 95 % CI (0.17, 0.61), P = 0.0006]. Low-quality evidence showed that PLIF resulted in a lower reoperation rate than PLF [OR 5.30, 95 % CI (1.47, 19.11), P = 0.01]. No statistical difference was found between the two groups with regard to blood loss [WMD = 76.52, 95 % CI (-310.68, 463.73), P = 0.70] and operating time [WMD = -1.20, 95 % CI (-40.36, 37.97), P = 0.95].

CONCLUSIONS

Moderate-quality evidence indicates that PLIF can improve the clinical satisfaction and increase the fusion rate compared to PLF. No superiority was found between the two fusion methods in terms of complication rate, amount of blood loss, and operating time for the treatment of lumbar spondylolisthesis.

Occupational benzene exposure and the risk of chronic myeloid leukemia: a meta-analysis of cohort studies incorporating study quality dimensions

OBJECTIVE

We documented previously that if study quality is accounted for, evidence from occupational cohort studies on benzene supports a possible association with some lymphoma subtypes, in particular multiple myeloma, and acute and chronic lymphocytic leukemia. Here, we extend these analyses to chronic myeloid leukemia (CML).

METHODS

Three strategies to assess study quality (stratification by the year-of-start of follow-up, stratification by the strength of the reported acute myeloid leukemia (AML) association, and stratification by the quality of benzene exposure assessment) were employed in a meta-analysis of occupational benzene exposure and CML. We hypothesized that stratification by these study quality dimensions would identify a subgroup of occupational cohort studies that is most informative for the evaluation of the possible association between benzene and CML.

RESULTS

The overall meta-relative risk (mRR) was non-significantly elevated (1.23; 95% confidence interval (CI): 0.93-1.63). The mRRs increased with increasing study quality for all dimensions with a significant elevation for studies with start of follow-up after 1970 (1.67; 95% CI: 1.02-2.74). The highest study quality stratum for AML significance and exposure quality showed an elevated but non-significant increased mRR (1.40; 95% CI: 0.86-2.27, and 1.68; 95% CI: 0.74-3.84, respectively).

CONCLUSIONS

Although limited by low statistical power, the current meta-analysis provides support for a possible association of occupational exposure to benzene and the risk of CML.

Applying quality criteria to exposure in asbestos epidemiology increases the estimated risk

Mesothelioma deaths due to environmental exposure to asbestos in The Netherlands led to parliamentary concern that exposure guidelines were not strict enough. The Health Council of the Netherlands was asked for advice. Its report has recently been published. The question of quality of the exposure estimates was studied more systematically than in previous asbestos meta-analyses. Five criteria of quality of exposure information were applied, and cohort studies that failed to meet these were excluded. For lung cancer, this decreased the number of cohorts included from 19 to 3 and increased the risk estimate 3- to 6-fold, with the requirements for good historical data on exposure and job history having the largest effects. It also suggested that the apparent differences in lung cancer potency between amphiboles and chrysotile may be produced by lower quality studies. A similar pattern was seen for mesothelioma. As a result, the Health Council has proposed that the occupational exposure limit be reduced from 10 000 fibres m(-3) (all types) to 250 f m(-3) (amphiboles), 1300 f m(-3) (mixed fibres), and 2000 f m(-3) (chrysotile). The process illustrates the importance of evaluating quality of exposure in epidemiology since poor quality of exposure data will lead to underestimated risk.

A meta-analysis of asbestos and lung cancer: is better quality exposure assessment associated with steeper slopes of the exposure-response relationships?

BACKGROUND

Asbestos is a well-recognized cause of lung cancer, but there is considerable between-study heterogeneity in the slope of the exposure-response relationship.

OBJECTIVE

We considered the role of quality of the exposure assessment to potentially explain heterogeneity in exposure-response slope estimates.

DATA SOURCES

We searched PubMed MEDLINE (1950-2009) for studies with quantitative estimates of cumulative asbestos exposure and lung cancer mortality and identified 19 original epidemiological studies. One was a population-based case-control study, and the others were industry-based cohort studies.

DATA EXTRACTION

Cumulative exposure categories and corresponding risks were abstracted. Exposure-response slopes [KL (lung cancer potency factor of asbestos)] were calculated using linear relative risk regression models.

DATA SYNTHESIS

We assessed the quality of five exposure assessment aspects of each study and conducted random effects univariate and multivariate meta-regressions. Heterogeneity in exposure-response relationships was greater than expected by chance (I2 = 64%). Stratification by exposure assessment characteristics revealed that studies with well-documented exposure assessment, larger contrast in exposure, greater coverage of the exposure history by exposure measurement data, and more complete job histories had higher meta-KL values than did studies without these characteristics. The latter two covariates were most strongly associated with the KL value. Meta-KL values increased when we incrementally restricted analyses to higher-quality studies.

CONCLUSIONS

This meta-analysis indicates that studies with higher-quality asbestos exposure assessment yield higher meta-estimates of the lung cancer risk per unit of exposure. Potency differences for predominantly chrysotile versus amphibole asbestos-exposed cohorts become difficult to ascertain when meta-analyses are restricted to studies with fewer exposure assessment limitations.

Main dietary compounds and pancreatic cancer risk. The quantitative analysis of case-control and cohort studies

OBJECTIVE

Estimation of the role of main dietary compounds in the risk of developing pancreatic cancer.

RESEARCH METHODS AND PROCEDURES

Literature published till 2010 was reviewed and selected for further analysis. The used terms were: red meat, minced meat, ham, bacon, sausages, white meat, poultry, vegetables, fish, eggs, fruits, lifestyle, diet, pancreatic cancer and pancreatic neoplasm. The collected data were meta-analysed with calculation of combined relative risk and 95% confidence interval as well as studies heterogeneity.

RESULTS

A meta-analysis of 11 case-control studies indicates that red meat ingestion elevates pancreatic cancer risk by 48% (95% CI=1.25-1.76). The vegetables and fruit reduce the risk by 38% (95% CI=0.54-0.73) and 29% (95% CI=0.59-0.84), respectively. The pooled analyses of 10 cohort studies do not show significant relations between main dietary compound ingestion and pancreatic cancer risk.

CONCLUSION

The red meat intake is associated with elevated risk of pancreatic cancer in contrast to vegetables and fruit ingestion. The ingestion of red meat, vegetables and fruit in cohort studies was not influenced on pancreatic cancer risk. The role of fish, poultry and eggs was not significant in both case-control and cohort studies, thus further studies were needed.

The impact of saturable metabolism on exposure-response relations in 2 studies of benzene-induced leukemia

Enzymatic saturation of metabolic pathways is one factor that potentially contributes to the nonlinear exposure-response relations that are frequently reported in occupational epidemiologic studies. The authors propose an approach to explore the contribution of saturable metabolism to previously reported exposure-response relations by integrating predictive models of relevant biomarkers of exposure into the epidemiologic analysis. The approach is demonstrated with 2 studies of leukemia in benzene-exposed workers, one conducted in the Australian petroleum industry (1981-1999) and one conducted in a US rubber hydrochloride production factory in Ohio (1940-1996). The studies differed greatly in their magnitudes and durations of exposure. Substitution of biomarker levels for external estimates of benzene exposure reduced the fold difference of the log relative risk of leukemia per unit of cumulative exposure between the 2 studies by 11%-44%. Nevertheless, a considerable difference in the log relative risk per unit of cumulative exposure remained between the 2 studies, suggesting that exposure misclassification, differences in study design, and potential confounding factors also contributed to the heterogeneity in risk estimates.

State of the art in benefit-risk analysis: food and nutrition

Benefit-risk assessment in food and nutrition is relatively new. It weighs the beneficial and adverse effects that a food (component) may have, in order to facilitate more informed management decisions regarding public health issues. It is rooted in the recognition that good food and nutrition can improve health and that some risk may be acceptable if benefit is expected to outweigh it. This paper presents an overview of current concepts and practices in benefit-risk analysis for food and nutrition. It aims to facilitate scientists and policy makers in performing, interpreting and evaluating benefit-risk assessments. Historically, the assessments of risks and benefits have been separate processes. Risk assessment is mainly addressed by toxicology, as demanded by regulation. It traditionally assumes that a maximum safe dose can be determined from experimental studies (usually in animals) and that applying appropriate uncertainty factors then defines the 'safe' intake for human populations. There is a minor role for other research traditions in risk assessment, such as epidemiology, which quantifies associations between determinants and health effects in humans. These effects can be both adverse and beneficial. Benefit assessment is newly developing in regulatory terms, but has been the subject of research for a long time within nutrition and epidemiology. The exact scope is yet to be defined. Reductions in risk can be termed benefits, but also states rising above 'the average health' are explored as benefits. In nutrition, current interest is in 'optimal' intake; from a population perspective, but also from a more individualised perspective. In current approaches to combine benefit and risk assessment, benefit assessment mirrors the traditional risk assessment paradigm of hazard identification, hazard characterization, exposure assessment and risk characterization. Benefit-risk comparison can be qualitative and quantitative. In a quantitative comparison, benefits and risks are expressed in a common currency, for which the input may be deterministic or (increasingly more) probabilistic. A tiered approach is advocated, as this allows for transparency, an early stop in the analysis and interim interaction with the decision-maker. A general problem in the disciplines underlying benefit-risk assessment is that good dose-response data, i.e. at relevant intake levels and suitable for the target population, are scarce. It is concluded that, provided it is clearly explained, benefit-risk assessment is a valuable approach to systematically show current knowledge and its gaps and to transparently provide the best possible science-based answer to complicated questions with a large potential impact on public health.

Meta-analysis of instrumented posterior interbody fusion versus instrumented posterolateral fusion in the lumbar spine

OBJECT

The authors compared the effectiveness of instrumented posterior lumbar interbody fusion (iPLIF) and instrumented posterolateral fusion (iPLF) for the treatment of low-back pain (LBP) due to degenerative lumbar disease.

METHODS

Relevant randomized controlled trials (RCTs) and comparative observational studies through December 2009 were identified using a retrieval strategy of sensitive and specific searches. The study design, participant characteristics, interventions, follow-up rate and period, and outcomes were abstracted after the assessment of methodological quality of the trials. Analyses were performed following the method guidelines of the Cochrane Back Review Group.

RESULTS

Nine studies were identified-3 RCTs and 6 comparative observational studies. No significant difference was found between the 2 fusion procedures in the global assessment of clinical outcome (OR 1.51, 95% CI 0.71-3.22, p = 0.29) and complication rate (OR 0.55, 95% CI 0.16-1.86, p = 0.34). Both techniques were effective in reducing pain and improving functional disability, as well as restoring intervertebral disc height. Instrumented PLIF was more effective in achieving solid fusion (OR 2.60, 95% CI 1.35-5.00, p = 0.004), a lower reoperation rate (OR 0.20, 95% CI 0.03-1.29, p = 0.09), and better restoration of segmental angle and lumbar lordotic angle than iPLF. There were no significant differences between the fusion methods regarding blood loss (weighted mean difference -179.63, 95% CI -516.42 to 157.15, p = 0.30), and operating time (weighted mean difference 8.03, 95% CI -45.46 to 61.53, p = 0.77).

CONCLUSIONS

The authors' analysis provided moderate-quality evidence that iPLIF has the advantages of higher fusion rate and better restoration of spinal alignment over iPLF. No significant differences were identified between iPLIF and iPLF concerning clinical outcome, complication rate, operating time, and blood loss.

Occupational cancer in developed countries

Studies of occupational exposures have made major contributions to our understanding of human carcinogenesis. About one third of the factors identified as definite or probable human carcinogens were first investigated in the workplace and these exposures exact a considerable toll on working populations. There are many additional workplace exposures that are suspect carcinogens that require further evaluation to ensure a safe work environment. Information from occupational investigations is also relevant to the general population because many occupational exposures can be found outside the workplace. Much of our understanding about occupational cancer has been obtained from studies largely composed of white men in developed countries. The movement of industry from developed to developing countries underscores the need for future investigations to include more diverse populations.

Occupational benzene exposure and the risk of lymphoma subtypes: a meta-analysis of cohort studies incorporating three study quality dimensions

BACKGROUND

The use of occupational cohort studies to assess the association of benzene and lymphoma is complicated by problems with exposure misclassification, outcome classification, and low statistical power.

OBJECTIVE

We performed meta-analyses of occupational cohort studies for five different lymphoma categories: Hodgkin lymphoma (HL), non-Hodgkin lymphoma (NHL), multiple myeloma (MM), acute lymphocytic leukemia (ALL), and chronic lymphocytic leukemia (CLL).

DATA EXTRACTION

We assessed three study quality dimensions to evaluate the impact of study quality variations on meta-relative risks (mRRs): stratification by the year of start of follow-up, stratification by the strength of the reported acute myelogenous leukemia association, and stratification by the quality of benzene exposure assessment.

DATA SYNTHESIS

mRRs for MM, ALL, and CLL increased with increasing study quality, regardless of the study quality dimension. mRRs for NHL also increased with increasing study quality, although this effect was less pronounced. We observed no association between occupational benzene exposure and HL.

CONCLUSIONS

Our meta-analysis provides support for an association between occupational benzene exposure and risk of MM, ALL, and CLL. The evidence for an association with NHL is less clear, but this is likely complicated by the etiologic heterogeneity of this group of diseases. Further consideration of the association between benzene and NHL will require delineation of risks by NHL subtype.

Leveraging Epidemiology to Improve Risk Assessment

The field of environmental public health is at an important crossroad. Our current biomonitoring efforts document widespread exposure to a host of chemicals for which toxicity information is lacking. At the same time, advances in the fields of genomics, proteomics, metabolomics, genetics and epigenetics are yielding volumes of data at a rapid pace. Our ability to detect chemicals in biological and environmental media has far outpaced our ability to interpret their health relevance, and as a result, the environmental risk paradigm, in its current state, is antiquated and ill-equipped to make the best use of these new data. In light of new scientific developments and the pressing need to characterize the public health burdens of chemicals, it is imperative to reinvigorate the use of environmental epidemiology in chemical risk assessment. Two case studies of chemical assessments from the Environmental Protection Agency Integrated Risk Information System database are presented to illustrate opportunities where epidemiologic data could have been used in place of experimental animal data in dose-response assessment, or where different approaches, techniques, or studies could have been employed to better utilize existing epidemiologic evidence. Based on the case studies and what can be learned from recent scientific advances and improved approaches to utilizing human data for dose-response estimation, recommendations are provided for the disciplines of epidemiology and risk assessment for enhancing the role of epidemiologic data in hazard identification and dose-response assessment.

Guidelines in dermatology--quo vadis?: Facts and controversies

Since their introduction in 1980s, medical guidelines have become a milestone in the modern medical practice and science. Being a key feature of modern evidence-based medicine, guidelines offer the opportunity for unification and standardization of diagnostic procedures, their use guarantees the equal access of patients to medical service, and they represent a scaffold for inexperienced physicians. The implementation of guidelines also can serve as a basis in malpractice issues and can contribute to the formation of national and international health care policies. In past decades, the process of development, update, and practical application of clinical guidelines has been seriously improved; however, certain limitations still exist, namely cost-effectiveness issues, editorial independence, applicability, accessibility, and external validity. This contribution discusses the advantages and the drawbacks in the use and the development of medical guidelines, emphasizing future perspectives and challenges in the development of clinical guidelines.

Flexible meta-regression to assess the shape of the benzene-leukemia exposure-response curve

BACKGROUND

Previous evaluations of the shape of the benzene-leukemia exposure-response curve (ERC) were based on a single set or on small sets of human occupational studies. Integrating evidence from all available studies that are of sufficient quality combined with flexible meta-regression models is likely to provide better insight into the functional relation between benzene exposure and risk of leukemia.

OBJECTIVES

We used natural splines in a flexible meta-regression method to assess the shape of the benzene-leukemia ERC.

METHODS

We fitted meta-regression models to 30 aggregated risk estimates extracted from nine human observational studies and performed sensitivity analyses to assess the impact of a priori assessed study characteristics on the predicted ERC.

RESULTS

The natural spline showed a supralinear shape at cumulative exposures less than 100 ppm-years, although this model fitted the data only marginally better than a linear model (p = 0.06). Stratification based on study design and jackknifing indicated that the cohort studies had a considerable impact on the shape of the ERC at high exposure levels (> 100 ppm-years) but that predicted risks for the low exposure range (< 50 ppm-years) were robust.

CONCLUSIONS

Although limited by the small number of studies and the large heterogeneity between studies, the inclusion of all studies of sufficient quality combined with a flexible meta-regression method provides the most comprehensive evaluation of the benzene-leukemia ERC to date. The natural spline based on all data indicates a significantly increased risk of leukemia [relative risk (RR) = 1.14; 95% confidence interval (CI), 1.04-1.26] at an exposure level as low as 10 ppm-years.

Endotoxin exposure and lung cancer risk: a systematic review and meta-analysis of the published literature on agriculture and cotton textile workers

Objective

To examine the association between exposure to endotoxins and lung cancer risk by conducting a systematic review and meta-analysis of epidemiologic studies of workers in the cotton textile and agricultural industries; industries known for high exposure levels of endotoxins.

Methods

Risk estimates were extracted from studies published before 2009 that met predefined quality criteria, including 8 cohort, 1 case–cohort, and 2 case–control studies of cotton textile industry workers, and 15 cohort and 2 case–control studies of agricultural workers. Summary risk estimates were calculated using random effects meta-analyses. Potential sources of heterogeneity were explored through subgroup analyses.

Results

The summary risk of lung cancer was 0.72 (95% CI, 0.57–0.90) for textile workers and 0.62 (0.52–0.75) for agricultural workers. The relative risk of lung cancer was below 1.0 for most subgroups defined according to sex, study design, outcome, smoking adjustment, and geographic area. Two studies provided quantitative estimates of endotoxin exposure and both studies tended to support a dose–dependent protective effect of endotoxins on lung cancer risk.

Conclusion

Despite several limitations, this meta-analysis based on high-quality studies adds weight to the hypothesis that occupational exposure to endotoxin in cotton textile production and agriculture is protective against lung cancer.