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Logo of oenvmedOccupational and Environmental MedicineVisit this articleSubmit a manuscriptReceive email alertsContact usBMJ
Occup Environ Med. 2007 December; 64(12): e32.
PMCID: PMC2095387

Silica and beryllium

166 Is it worth doing research to develop awareness and information materials? A case study of silicosis elimination in South Africa

D. Rees. National Institute for Occupational Health

ObjectivesDust control is fundamental to the elimination of silicosis, but awareness and information are necessary to drive its implementation. Materials to inform and create awareness are common, but few are underpinned by research on the target groups and are thus not directed at issues important in overcoming barriers to improved practice. Hence this formative research commissioned by South Africa's Mine Health and Safety Council to develop materials for health and safety representatives (representatives), mine workers and mine management. This paper presents examples of research findings from representatives and mine workers and considers the value of doing the research.

MethodsA structured questionnaire was administered to 260 representatives in their preferred language on 10 gold mines from three major companies to explore knowledge and perceptions about dust diseases, and perceptions of representatives' role in promoting dust control. Fifteen focus groups were conducted with mine workers to determine knowledge and to identify barriers to behaviour change.

ResultsForty per cent of representatives had 7 or fewer years of formal education (a basic literacy index); 65% did not know the word silicosis (non‐specific terms were used); their advocacy role was not appreciated (only a small minority understood systems for reporting dust problems). Computer‐aided training was the method liked least by representatives. Mine workers' knowledge about most aspects of dust, silicosis control and diseases was at best vague with dangerous misconceptions. There was a lack of trust of management, unions, representatives and health services. Production bonuses or quotas were seen to be paramount; under these conditions, safety and health (dust control) was not seen as a priority.

ConclusionThe nature and content of materials and support activities to promote dust control were substantially influenced by research findings, for example, to build self‐efficacy and stress long‐term health benefits over short‐term financial gain. The formative research cost about US$200 000, a small investment relative to the cost of production and distribution of materials for an industry employing over 500 000 people. Occupational epidemiologists in poorer countries may need to consider using “cultural epidemiology” to promote occupational health.

Key wordsresearch value; awareness materials; silicosis

167 Meta‐analyses of published epidemiological studies (1979 and 2006) point to open causal questions in silica‐lung cancer research

T. C. Erren1, C. B. Glende1, P. Morfeld1, P. Cocco2, A. H. Smith3, C. Steinmaus3, C. Piekarski1. 1University of Cologne; 2University of Cagliari; 3University of California, Berkeley

ObjectivesHere we update meta‐analyses of silicosis and lung cancer, present the first detailed meta‐analysis of risks in individuals without silicosis and specify necessary future research. The topic is critical to public health decision making concerning silica, classified as an IARC group 1 carcinogen since 1997: if silicosis is required to increase lung cancer risks, then the goal should be to prevent silicosis; but if it is not required, then lung cancer risks may be increased at much lower doses of silica not known to cause detectable silicosis.

MethodsIn order to explore significant discrepancies between studies, and to ultimately decide which, if any, study results could be aggregated in meaningful summary estimates, we calculated fixed‐effects summaries and random‐effects summaries and their respective 95% confidence intervals and also adopted a regression approach.

ResultsIn silicotics, lung cancer risks were found to be doubled in 38 studies (fixed‐effects summaries (FES): RR 2.1, 95% CI 2.0 to 2.3; random‐effects summaries (RES): RR 2.1, 95% CI 1.9 to 2.3). In non‐silicotics, eight studies without smoking adjustment suggested marginally elevated risks but three studies which controlled for smoking showed null results (FES and RES: RR 1.0; 95% CI 0.8 to 1.3). Heterogeneity between studies was substantial but could be linked to study characteristics and second‐level data in meta‐regression.

ConclusionOverall, our meta‐analyses further substantiate the already ample evidence collected prior to 1997 of a strong association between silicosis and lung cancer but questions regarding lung cancer caused by silica alone remain: indeed, silicosis may be required for the development of silica‐associated cancer because of underlying lung alterations. Moreover, it could be a biomarker of relevant exposures and of susceptibility to lung carcinogens. We conclude that further studies are needed to fill our gaps of knowledge in silica‐silicosis‐lung cancer research. Ideally, future investigations should consider the entire exposure–response range between silica exposure, silicosis development and lung cancer occurrence, and analyse data in terms of processes taking intermediate confounding into account.

Key wordssilica; lung cancer; meta‐analyses

168 A simple diagnostic model for early detection of pneumoconiosis in natural stone and construction workers

E. Meijer. Institute for Risk Assessment Sciences, Utrecht University

ObjectivesTo detect silicosis in an early phase among workers exposed to silica‐containing dust, regular health monitoring is needed. Protocols exist but none specifies the sequential diagnostic work‐up. This will result in abundant unnecessary x rays. The aim of this study was to develop a diagnostic model from simple questionnaire items and spirometry that can be used as a screening instrument. The model should quantify the independent contribution of different predictors to detect chest x ray abnormalities indicative for pneumoconiosis.

MethodsThe study was performed using cross‐sectional data of 1291 Dutch natural stone and construction workers with potentially high quartz dust exposure. A multivariable logistic regression model was developed using chest x ray with ILO profusion category >1/1 as the reference standard. The diagnostic accuracy of the developed model was evaluated and a bootstrapping procedure was done to assess its internal validity. For clinical application, the diagnostic model was transformed into an easy‐to‐use score chart.

ResultsAge 40 years or older, current smoker, high exposed job title, working 15 years or longer in the construction industry, “feeling unhealthy”, and standardised residual FEV1 were to be independent predictors in the diagnostic model. The model showed good calibration and discriminative ability (area under receiver operating characteristic curve (AUC) 0.81, 95% CI 0.74 to 0.85). Internal validity was reasonable (correction factor of 0.82, optimism corrected AUC 0.76). By using a sum score with a high negative predictive value, the occupational physician could efficiently exclude a large fraction of workers with a low probability of having pneumoconiosis from unnecessary x ray investigations.

ConclusionOur diagnostic model proved to be an efficient and effective instrument to rule out pneumoconiosis among construction workers. Its use in health surveillance among these workers could minimise the number of redundant x ray investigations.

Key wordsdiagnostic model; silicosis; construction workers

169 Silica, radiographic silicosis, and lung cancer in Western Australian goldminers

N. H. de Klerk1, A. W. Musk2. 1University of Western Australia; 2Sir Charles Gairdner Hospital, Perth

ObjectivesPrevious mortality studies of gold miners from Kalgoorlie in Western Australia (WA) suggested that the excess risk of lung cancer occurred only among workers who had been compensated for silicosis. We aimed to determine whether radiographically diagnosed silicosis rather than clinically diagnosed silicosis also accounted for the excess lung cancer.

MethodsCumulative exposures to respirable silica were derived using a method to standardise over 550 dust particle counts taken from mines in WA during the 1950s with subjective dust exposure rankings for over 400 jobs. All x rays for all miners were sought from the Perth Chest Clinic and x ray packets, with between 1 and 41 x rays in each packet, were found for 1785 miners with complete work histories. These were scored according to the ILO classification of the pneumoconioses by three trained readers and the median score taken. Mortality and cancer incidence were assessed by linking to the WA Death and Cancer Registries, the National Death Index and the National Cancer Clearing House. The association of silica exposure with incidence of lung cancer was estimated using age and year matched conditional logistic regression analyses, before and after adjustment for both radiographic and clinical silicosis using propensity score matching for each of these intervening diseases.

Results156 cases of lung cancer occurred. 30% of miners with ILO category profusion of small opacities 1/0 or greater received no compensation and 30% of compensated workers did not have silicosis on their x ray. There was a strong and consistent effect of estimated exposure to respirable silica on incidence of silicosis, and a much lesser effect on lung cancer. The presence of silicosis was associated with increased lung cancer mortality whether diagnosed only on x ray or by the compensation board. After adjustment for silicosis, the effect of respirable silica on lung cancer was reduced to the same level as found in a large IARC pooled study.

ConclusionThis study agrees with previous findings of a small but important effect of exposure to silica on lung cancer, irrespective of a diagnosis of silicosis.

Key wordslung cancer; quartz; mining

170 Compensation for beryllium‐related conditions in Quebec between 1999 and 2002

F. P. Labreche, L. De Guire, S. Provencher. Institut National de Santé Publique du Québec

ObjectivesTo estimate the incidence of beryllium‐related conditions using workers' compensation files in the province of Québec and to describe characteristics, test results, signs and symptoms associated with the presence or absence of beryllium‐related conditions among these workers.

MethodsA chart review of all compensation claims filed between 1999 and 2002 for a beryllium‐related occupational disease was carried out. Data on socio‐demographic characteristics, diverse diagnostic tests, symptoms and work history were abstracted from administrative compensation charts.

ResultsDuring the time period under study, 68 workers filed a compensation claim: 23% were diagnosed with chronic beryllium disease (CBD), 18% with sub‐clinical beryllium disease (SBD) and 31% with beryllium sensitisation (BS); the health conditions of the remaining 28% were considered to be unrelated to beryllium exposure. Nine workers were evaluated more than once by occupational chest physicians during that 4‐year span: for two of them, the compensation decision was changed from no beryllium‐related condition to either sensitisation or SBD, and for one of the nine workers, a sensitisation became a SBD. Reported symptoms were mostly non‐specific; however, workers with CBD presented dyspnoea (31%), fatigue (25%), rales (19%) and wheezing (19%) more frequently than workers diagnosed with other beryllium‐related conditions; their medical imaging tests were more often abnormal, and so were their bronchoalveolar lavage fluid lymphocytosis compared to that of workers with SBD. These numbers correspond to a rough annual incidence rate estimate of 66 cases of berylliosis (CBD plus SBD) and of 49 cases of sensitisation per 100 000 exposed workers. Workers with a beryllium‐related disease had been exposed to the metal for an average of 18 years, compared to workers with health complaints unrelated to beryllium, who had been exposed for 12 years on average. For most compensated workers, beryllium exposure occurred in the primary metal manufacturing industry (63%) and in the construction and prime contracting industries (21%).

ConclusionThis analysis underlines the diversity of clinical presentations of beryllium‐related conditions. Although compensation files present limitations regarding exhaustiveness of workers coverage, their analysis can give valuable information on the natural history of the beryllium‐related diseases and their clinical investigation in relation to exposure in the workplace

Key wordschronic beryllium disease; lymphocyte proliferation test; surveillance

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