Silica, compensated silicosis, and lung cancer in Western Australian goldminers

OBJECTIVES

Silica has recently been reclassified as carcinogenic to humans based largely on the observed increase in rates of lung cancer in subjects with silicosis. Other recent reviews have arrived at different conclusions as to whether silicosis or silica itself is carcinogenic. This study aims to examine exposure-response relations between exposure to silica and subsequent silicosis and lung cancer in a cohort of goldminers.

METHODS

2,297 goldminers from Kalgoorlie in Western Australia were examined in 1961, 1974, and 1975. Data were collected on respiratory symptoms, smoking habits, and employment history. Subjects were followed up to the end of 1993. Survival analyses for lung cancer mortality and incidence of compensated silicosis were performed with age and year matched conditional logistic regression analyses.

RESULTS

89% of the cohort were traced to the end of 1993. 84% of the men had smoked at some time and 66% were current smokers. 1386 deaths occurred during the follow up period, 138 from lung cancer, and 631 subjects were compensated for silicosis. A strong effect of smoking on mortality from lung cancer, and a smaller effect on the incidence of compensated silicosis was found. There was a strong effect of duration and intensity of exposure on the incidence of silicosis. The risk of mortality from lung cancer increased after compensation for silicosis. Of all direct measures of exposure to silica, only log cumulative exposure was significantly related to incidence of lung cancer, but this effect disappeared once the onset of silicosis was taken into account.

CONCLUSIONS

The incidence of silicosis was clearly related to exposure to silica and the onset of silicosis conferred a significant increase in risk for subsequent lung cancer, but there was no evidence that exposure to silica caused lung cancer in the absence of silicosis.

Vitamin A and cancer prevention I: observations in workers previously exposed to asbestos at Wittenoom, Western Australia

Our aim was to describe a vitamin A-based cancer prevention program for former asbestos workers and to check for possible harmful effects by comparing rates of disease and death in study subjects with subjects who chose not to join. All subjects had been occupationally exposed to crocidolite at Wittenoom Gorge between 1943 and 1966; 1,677 subjects indicated interest in the program and 1,203 joined between June 1990 and May 1995. Comparison subjects consisted of 996 former workers known to be alive in Western Australia in 1990 who did not join the program. Program subjects were provided with annual supplies of vitamin A (either synthetic beta-carotene or retinol), help in quitting smoking and dietary advice. The comparison group received only mail contact. Both groups were followed up to December 1994 for vital status and cancer information, and rates of cancer and death from various causes were compared. Mortality in both groups was higher than expected (standardised mortality ratio 1.23 in program subjects and 1.67 in comparison subjects). After adjustment for age, smoking and asbestos exposure, the relative rates in participants compared with non-participants was below I for all examined cancers and causes of death. For mesothelioma and lung cancer, group differences increased with time from entry, whereas other differences dissipated with time. No significant side effects were reported. In conclusion, program participants had significantly lower mortality than non-participants, but the rates of the 2 groups converged with time.

Vitamin A and cancer prevention II: comparison of the effects of retinol and beta-carotene

Former blue asbestos workers known to be at high risk of asbestos-related diseases, particularly malignant mesothelioma and lung cancer, were enrolled in a chemo-prevention program using vitamin A. Our aims were to compare rates of disease and death in subjects randomly assigned to beta-carotene or retinol. Subjects were assigned randomly to take 30 mg/day beta-carotene (512 subjects) or 25,000 IU/day retinol (512 subjects) and followed up through death and cancer registries from the start of the study in June 1990 till May 1995. Comparison between groups was by Cox regression in both intention-to-treat analyses and efficacy analyses based on treatment actually taken. Median follow-up time was 232 weeks. Four cases of lung cancer and 3 cases of mesothelioma were observed in subjects randomised to retinol and 6 cases of lung cancer and 12 cases of mesothelioma in subjects randomised to beta-carotene. The relative rate of mesothelioma (the most common single cause of death in our study) for those on retinol compared with those on beta-carotene was 0.24 (95% CI 0.07-0.86). In the retinol group, there was also a significantly lower rate for death from all causes but a higher rate of ischaemic heart disease mortality. Similar results were found with efficacy analyses. Our results confirm other findings of a lack of any benefit from administration of large doses of synthetic beta-carotene. The finding of significantly lower rates of mesothelioma among subjects assigned to retinol requires further investigation.

A genome scan for loci influencing total serum immunoglobulin levels: possible linkage of IgA to the chromosome 13 atopy locus

Immunoglobulins play an essential part in the immune system, and immunoglobulin deficiencies can have profound medical consequences. The genetic control and regulation of the immunoglobulin response is therefore of interest. Previous investigations have identified a number of loci influencing total and specific IgE levels. In this study, 80 nuclear families have been examined for linkage of total serum IgA, IgG and IgM levels to a genome-wide panel of microsatellite markers. Potential quantitative trait loci influencing IgA levels have been identified on chromosomes 10 and 13, and possible loci influencing IgG levels were found on chromosomes 3 and 13. No significant linkages to IgM levels were found. The linkage of IgA on chromosome 13 was to a marker previously linked to IgE responses (atopy). Linkage to IgG was in the same region but to a more distal marker. None of the factors known to influence immunoglobulin expression map to the loci identified in the present study. These loci are therefore likely to contain previously unrecognized components of the immunoregulatory system.

Environmental exposure to crocidolite and mesothelioma: exposure-response relationships

This study aimed to estimate exposure-response relationships for mesothelioma and environmental exposure to crocidolite. All 4,659 former residents of Wittenoom, Western Australia (WA) who lived there between 1943 and 1993 for at least 1 mo and were not directly employed in the crocidolite industry, were followed-up through the WA death, cancer and mesothelioma registries, electoral rolls, and telephone books. In 1992, all subjects who should be traced were sent a questionnaire. Exposure levels were estimated from results of periodic environmental surveys and duration of residence. Incidence rates were standardized to the World Population and Cox Regression was used to estimate the effects of exposure on incidence. To the end of 1993, 27 cases of mesothelioma were diagnosed. Mesothelioma cases stayed longer at Wittenoom, had a higher average intensity of exposure, and a higher cumulative exposure to crocidolite than control subjects. The standardized incidence of mesothelioma was 260 per million person-years, and was similar for males and females. The rate increased significantly with time from first exposure, duration of exposure and cumulative exposure. At these levels of crocidolite exposure, there is a significantly increased risk of mesothelioma, which is dose-dependent.

Risk factors for the development of non-response to first-line treatment for tuberculosis in southern Vietnam

BACKGROUND

Acquired resistance to standard chemotherapy for tuberculosis (TB) is an increasing problem worldwide. Vietnam has one of the highest incidences of TB and also has a large population of potential migrants to other countries. Since 1979 the International Organisation for Migration (IOM) has been running a supervised programme of TB treatment for intending migrants from Vietnam where few facilities for bacteriological culture and sensitivity testing exist. This study aimed to assess the most important factors for predicting non-response to first-line treatment as treatment starts and whether any further indicators occur during the course of treatment which may enable more accurate prediction of non-response.

METHODS

In all, 130 subjects failing to respond to first-line therapy (cases) between 1990 and 1995 were compared with 673 subjects who responded to therapy (controls) on various demographic and clinical characteristics using logistic regression to create a prognostic index. Variables analysed included the patient history of past TB treatment, weight, age, sex and radiological and bacteriological findings. All subjects also tested negative for HIV status.

RESULTS

The chief markers of successful response were x-ray signs and degree of sputum smear positivity. These markers provided a prognostic index with an optimal cutoff providing about 70% sensitivity and 80% specificity. Incorporating further measures obtained through the first 3 months of treatment improved the sensitivity to 80%.

CONCLUSION

While this study enabled prediction of the majority of subjects failing to respond to first-line therapy, other factors need to be assessed before recommendations for altering treatment regimens can be made. The prognostic index could be useful in assessing subjects for closer supervision.

Fc epsilon R1-beta polymorphism and total serum IgE levels in endemically parasitized Australian aborigines

Endemic helminthic infection is a major public-health problem and affects a large proportion of the world's population. In Australia, helminthic infection is endemic in Aboriginal communities living in tropical northern regions of the continent. Such infection is associated with nonspecific (polyclonal) stimulation of IgE synthesis and highly elevated total serum IgE levels. There is evidence that worm-infection variance (i.e., human capacity of resistance) and total serum IgE levels may be related to the presence of a major codominant gene. The beta chain of the high-affinity IgE receptor, Fc epsilon R1-beta, has been previously identified as a candidate for the close genetic linkage of the 11q13 region to IgE responses in several populations. We show a biallelic RsaI polymorphism in Fc epsilon R1-beta to be associated with total serum IgE levels (P = .0001) in a tropical population of endemically parasitized Australian Aborigines (n = 234 subjects). The polymorphism explained 12.4% of the total residual variation in serum total IgE and showed a significant (P = .0000) additive relationship with total serum IgE levels, across the three genotypes. These associations were independent of familial correlations, age, gender, racial admixture, or smoking status. Alleles of a microsatellite repeat in intron 5 of the same gene showed similar associations. The results suggest that variation in Fc epsilon R1-beta may regulate IgE-mediated immune responses in this population.

Comparison of oral bambuterol and terbutaline in elderly patients with chronic reversible airflow obstruction

Bambuterol, a carbamate prodrug of terbutaline, is the first once-daily oral beta 2-agonist. The effect/side effect ratio of bambuterol oral solution was compared with terbutaline mixture in elderly patients with chronic reversible obstructive airways disease. The study was of a double-blind, crossover, randomized design and consisted of a 4-7-day run-in period followed by four consecutive treatment periods each of 2 weeks. The treatments were bambuterol solution 20 mg nocte (B20), 10 mg nocte (B10), terbutaline mixture 3 mg t.i.d., (T), and placebo solution (P). Patients measured daily peak expiratory flow rate (PEFR), asthma symptoms, use of inhaled beta 2-agonist, and tremor. Of 84 patients, 66 completed all periods. Mean age was 67 years (60-90), basal FEV1 1.49 L, and reversibility of FEV1 30%. Ninety-four percent of the patients used inhaled/oral steroids in constant dosage. All treatments were significantly more effective than placebo. B20 resulted in higher morning PEFR than T (306 +/- 2.9 L/min vs. 297 +/- 2.9 L/min), while B10 gave equivalent results to T. No differences were seen in the use of inhaled beta 2-agonist. Less shortness of breath was experienced during the night with B20 and during the day with B10 compared with placebo. Both B20 and T produced more tremor than B10 and P. In elderly patients with chronic reversible airways obstruction once-daily bambuterol (10-20 mg) has a better effect/side effect ratio than 3 mg terbutaline thrice daily.

Comparison of measures of exposure to asbestos in former crocidolite workers from Wittenoom Gorge, W. Australia

Determinations of exposure-response relationships between crocidolite and the major asbestos-related diseases in the Wittenoom cohort have previously depended on the validity of estimates of airborne exposure to asbestos. This work aims to validate the airborne exposure measurements by obtaining measurements of the concentrations of uncoated crocidolite fibers and asbestos bodies retained in the lungs of individual workers, and to estimate the half-life of crocidolite fibers in the lungs. Samples of lung tissue, excluding tumor, of all former Wittenoom workers known to have died in Western Australia (WA) were sought from teaching hospitals, pathology departments, and the Coroner's pathologist. The lung specimens were processed using Pooley's method with TEM for counts of fibers of all types and using Smith and Naylor's method with conventional light microscopy for asbestos bodies (AB). Multiple linear regression was utilized to examine the associations between crocidolite concentrations in the lung and duration of employment at Wittenoom, time since last employed at Wittenoom, nature of job, estimated average fiber concentration at the worksite, and estimated cumulative crocidolite exposure (CCE) in fiber-years/ml for each subject. Lung tissue from 90 cases was processed and there was good agreement between counts of crocidolite fibers, asbestos bodies, and CCE. Correlations were 0.77 for AB and fibers, 0.54 for AB and CCE, and 0.58 for CCE and fibers, after log transformation. The half-life of crocidolite fibers in the lung was estimated at 92 months (95% CI 55-277 months). Previous estimates of airborne exposure to Wittenoom crocidolite have been reasonably reliable. The relatively simple technique of light microscopy for counting ABs in lung tissue also provides a useful and reliable indication of the level of past occupational exposure to crocidolite in subjects whose exposure has been only to crocidolite. The half-life of crocidolite fibers in the lungs of former Wittenoom workers is about 7-8 years.

A genome-wide search for quantitative trait loci underlying asthma

Asthma now affects one child in seven in the United Kingdom. Most cases (95%) of childhood asthma are associated with atopy, the immunoglobulin E (IgE)-mediated familial syndrome of allergic asthma, eczema and rhinitis. Segregation analysis has consistently suggested the presence of major genes influencing atopy and IgE levels, with the expectation that these genes may be identified by positional cloning or the examination of candidate genes. Here we report the results of a genome-wide search for linkage to one qualitative and four quantitative traits associated with allergic (atopic) asthma. We have identified six potential linkages (P<0.001), five of which are to quantitative traits. Monte Carlo simulations show that 1.6 false-positive linkages at this level of significance would be expected from the data. One linkage, to chromosome 11q13, has been established previously. Three of the new loci show evidence of linkage to a second panel of families, in which maternal effects and pleiotropy of linked phenotypes are seen. The results demonstrate the extent and the complexity of the genetic predisposition to asthma.

Exposure to crocidolite and the incidence of different histological types of lung cancer

OBJECTIVES

To estimate the relations between exposure to both tobacco smoke and crocidolite and the incidence of various histological types of lung cancer.

METHODS

In 1979 all former workers from the Wittenoom asbestos industry who could be traced were sent a questionnaire on smoking history. Of 2928 questionnaires sent, satisfactory replies were received from 2400 men and 149 women. Of the men, 80% had smoked at some time and 50% still smoked. Occupational exposure to crocidolite was known from employment records and follow up was maintained through death and cancer registries in Australia with histological diagnoses obtained from the relevant State Cancer Registry. Conditional logistic regression was used to estimate the effects of tobacco and asbestos exposure on incidence of different cell types of lung cancer in a nested case-control design.

RESULTS

Between 1979 and 1990, 71 cases of lung cancer occurred among men in this cohort: 27% squamous cell carcinoma, 31% adenocarcinoma, 18% small cell carcinoma, 11% large cell carcinoma, and 13% unclassified or indeterminate. Two of the classified cases and one unclassified case had never smoked. The incidence of both squamous and adenocarcinoma types of lung cancer were greatest in ex-smokers and in those subjects with the highest levels of exposure to crocidolite. After adjustment for smoking habit, the increase in incidence of lung cancer with increasing exposure to crocidolite was greater for squamous cell carcinoma than for adenocarcinoma.

CONCLUSIONS

The results from this study have shown significant exposure-response effects for exposure to crocidolite, and both adenocarcinoma and squamous cell carcinoma of the lung. They also provide some further evidence against the theory that parenchymal fibrosis induced by asbestos is a necessary precursor to asbestos induced lung cancer.

Asbestos bodies in lung tissue following exposure to crocidolite

A series of 206 necropsies in Western Australia (WA) have had routine counts made of asbestos bodies in samples of lung tissue using conventional light microscopy. Thirty-two cases had worked in the asbestos industry at Wittenoom, WA and (log) counts of asbestos bodies in their lung tissue correlated well with estimates of their (log) cumulative airborne exposure to crocidolite fibers (r = 0.60). There was no association between the number of asbestos bodies and time since exposure to asbestos ceased. In subjects without known exposure to asbestos, there was a weak but nonsignificant increase in number of asbestos bodies with increasing age, with 26% of cases having no asbestos bodies present. It is concluded that the relatively simple technique of light microscopy for counting of asbestos bodies in lung tissue provides a reliable indication of the level of past occupational exposure to crocidolite in subjects whose exposure has been only to crocidolite. This could be extremely useful in follow-up studies of cohorts that lack reliable measures of airborne exposure to crocidolite asbestos.

Malignant mesothelioma in Pilbara Aborigines

Malignant mesothelioma occurred in a female Aborigine after environmental exposure to asbestos. All known cases of the disease in Aborigines in Western Australia were reviewed; all occurred in Pilbara residents. Most were exposed while involved in the transport of asbestos from the Wittenoom crocidolite operation. Based on recent estimates of the size of the Aboriginal population in the Pilbara region, their incidence of this disease (250 per million for ages 15 and over) is one of the highest population-based rates recorded.

Fc epsilon RI-beta polymorphism and risk of atopy in a general population sample

OBJECTIVE

To establish the prevalence of Fc epsilon RI-beta polymorphisms Leu181 and Leu181/Leu183 on chromosome 11q13 in the general population and to examine whether when maternally inherited they confer a risk of atopy.

DESIGN

A population based survey for measures of atopy (skin prick test reactions, specific IgE titres, total serum IgE concentration), bronchial hyperresponsiveness, and carriage of Fc epsilon RI-beta Leu181 and Leu181/Leu183.

SETTING

The rural coastal town of Busselton, Western Australia.

SUBJECTS

1004 members of 230 two generation families identified through adults aged under 55.

RESULTS

Fc epsilon RI-beta Leu181/Leu183 was identified in 45 subjects (4.5%). All 13 children who had inherited the variant maternally were atopic. Six had asthma and nine rhinitis. The odds ratio of a positive skin prick test reaction to house dust mite or grass pollen in these children compared with the other 523 children was 7.37 (95% confidence interval 1.62 to 33.60). The 95% confidence interval for the odds ratio of a positive specific IgE response (radio-allergosorbent test) was 3.00 to infinity, and the odds ratio for bronchial hyperresponsiveness was 3.70 (1.21 to 11.60). By contrast, the eight children who had derived the variant paternally had negative skin prick and radioallergosorbent test results and did not have increased bronchial responsiveness.

CONCLUSION

Fc epsilon RI"' beta Leu181/Leu183 when inherited maternally identifies a genetic risk factor for atopy and bronchial hyperresponsiveness.

Potential for interferon-alpha-based therapy in mesothelioma: assessment in a murine model

Malignant mesothelioma is an aggressive tumor, usually induced by asbestos exposure, that has a poor prognosis and is unresponsive to conventional therapy. The present study was aimed at assessing the potential for interferon-alpha (IFN-alpha)-based therapies in a murine model for malignant mesothelioma. The effect of recombinant human IFN-alpha B/D on tumor growth, alone and in combination with either of two immunomodulatory and antiproliferative agents beta-carotene or alpha-difluoromethylornithine (DFMO), was assessed. The data suggest that IFN-alpha treatment is most efficacious when commenced early in tumor development. Combination of IFN-alpha with either DFMO or dietary beta-carotene supplementation improved the effect of an otherwise suboptimal IFN-alpha therapy regimen. Both IFN-alpha and beta-carotene had in vivo stimulatory effects on immune cells, perhaps indirectly by inhibiting TGF-beta generation. The immunomodulatory effects may contribute, at least in part, to the positive antitumor and clinical activities of the treatments in this model.

Detection of a recessive major gene for high IgE levels acting independently of specific response to allergens

The genetic control of the total IgE, the immunoglobulins E involved in allergy, remains still unclear. Although high IgE levels were found to be determined by a recessive major gene in several studies, other modes of inheritance were also reported. Moreover, at least two different genetic mechanisms controlling the IgE regulation have been suggested: one involved in the specific IgE response and the other one in the nonspecific response. To better understand the genetic mechanisms controlling IgE variation, we performed segregation analysis of IgE levels by ignoring or taking into account the specific response to allergens (SRA). Analyses were conducted using the class D regressive model, in a sample of 234 Australian nuclear families randomly selected during the winter months, when IgE levels are the lowest (basal). SRA, when included as a covariate in the model, was defined by one of the three following criteria: (1) raised specific IgE level for one or more allergens, (2) positive skin test for one or more allergens, and (3) at least one of the (1) or (2) criteria. When the presence of SRA is ignored, the familial transmission of total IgE level is compatible with the segregation of a recessive major gene and residual familial correlations. When the presence of SRA is accounted for in the analysis, whether defined by criteria (1), (2), or (3), there is still evidence for a recessive major gene controlling IgE levels but residual familial correlations are no longer significant. In addition, no interaction between this major gene and SRA is shown here. Our results suggest that this gene, which accounts for 28% of the variation of the trait, may be involved in the control of basal IgE production, independently of specific response to allergens.

Genetic linkage of T-cell receptor alpha/delta complex to specific IgE responses

IgE responses to inhaled proteins underlie the clinical syndrome of allergic (atopic) asthma and rhinitis. We have investigated genetic linkage between specific IgE reactions to highly purified major allergens and the T-cell receptor (TCR) alpha and beta gene complexes on chromosome 14 and 7, respectively. Antigens tested included highly purified proteins from the housedust mite Dermatophagoides pteronyssinus, the domestic cat and dog, grass pollen, and the mould Alternaria alternata. Affected sibling-pair methods were used in two independent sets of families, one in the UK and one in Australia. No linkage of IgE serotypes to TCR-beta was detected, but significant linkage to TCR-alpha was seen in both family groups. For several of the IgE phenotypes investigated (positive responses to whole allergen sources or purified antigens or serum IgE above the 70th percentile in the population) the affected sibling-pairs showed significant sharing of TCR-alpha microsatellite alleles from both parents. The results show that a gene (or genes) in the TCR-alpha region modifies specific IgE responses.

Progress on smoking control in Western Australia

In 1990, 20 years of campaigning by the Western Australian branch of the Australian Council on Smoking and Health succeeded in getting tobacco advertising banned in Western Australia and a fund set up to replace the sponsorship of sport by tobacco companies. The council coordinated the activities of the mainly professional medical organisations that formed its members, ensuring that messages about the dangers of tobacco were consistently presented from different angles. The campaigners also ensured that medical data were reworked for presentation to decision makers and public, invaded the corporate world, and minimised opposition by enlisting the support of sportspeople opposed to tobacco sponsorship. The council hopes now that elimination of advertising will reduce the prevalence of smoking.

Interferon alpha and doxorubicin in malignant mesothelioma: a phase II study

BACKGROUND

Malignant mesothelioma is a tumour which is generally resistant to chemotherapy. While the addition of interferon to chemotherapy improves response rates in some other malignancies, such a combination has not been evaluated in the treatment of mesothelioma.

AIMS

To assess the anti-tumour effects and toxicity of interferon-alpha combined with doxorubicin in the treatment of pleural mesothelioma.

METHODS

Twenty five patients (mean age 54 +/- 11 years) were enrolled in a phase II study. All patients had a confirmed histological diagnosis, measurable tumour, a life expectancy of at least three months, and no prior chemotherapy or interferon. Interferon alpha-2a, 9 x 10(6) U sc daily, was administered together with doxorubicin 25 mg per m2 i.v. weekly, for 12 weeks. Response status was assessed by tumour measurements on clinical examination and thoracic CT scans before and after treatment.

RESULTS

A partial response was observed in four patients (16%; 90% CI, 8-30%), 11 remained stable, while six had progressive disease. Four patients withdrew within the first month because of toxicity. The median survival of all patients was 11 months (95% CI, 3-19). Dose modification as a result of toxicity was required in all patients. Lethargy, weight loss, leukopenia and vomiting were the most common side effects.

CONCLUSIONS

The combination of interferon-alpha and doxorubicin showed only modest activity and was associated with significant toxicity. It cannot be recommended in the treatment of malignant pleural mesothelioma.

Radiographic abnormalities and mortality in subjects with exposure to crocidolite

Plain chest radiographs from a one in six random sample of the workforce of the asbestos industry at Wittenoom, Western Australia between 1943 and 1966 have been classified for degree of profusion and pleural thickening by two independent observers according to the 1980 UICC-ILO Classification of Radiographs for the pneumoconioses to clarify the effect of degree of radiological abnormality on survival. A total of 1106 subjects were selected. Each subject's age, cumulative exposure to crocidolite, and time since first exposure were determined from employment records, the results of a survey of airborne concentrations of fibres > 5 mu in length conducted in 1966, and an exposure rating by an industrial hygienist and an ex-manager of the mine and mill at Wittenoom. By the end of 1986 193 subjects had died. Conditional logistic regression was used to model the relative risk of death in five separate case-control analyses in which the outcomes were deaths from: (1) all causes, (2) malignant mesothelioma, (3) lung cancer, (4) asbestosis, and (5) other causes excluding cancer and asbestosis. Up to 20 controls per case were randomly chosen from all men of the same age who were not known to have died before the date of death of the index case. After adjustment for exposure and time since first exposure, there were significant and independent effects of radiographic profusion and pleural thickening on all cause mortality. The effect of profusion was largely a result of the effect on mortality from malignant mesothelioma and asbestosis but not lung cancer. The effect of pleural thickening was greatest on mortality from other causes, mainly ischaemic heart disease. This study has shown that degree of radiographic abnormality has an independent effect on mortality from malignant mesothelioma, asbestosis, and all causes even after allowing for the effects of age, degree of exposure, and time since first exposure.

Malignant mesothelioma after environmental exposure to blue asbestos

To determine the magnitude of the population at risk from non-occupational exposure to crocidolite at Wittenoom, Western Australia (WA), a cohort of 4,890 residents who never worked for the mining company Australian Blue Asbestos (ABA) has been assembled from all 18,553 available records: the local school register, hospital attendances, the WA electoral roll, birth certificates, workers who answered a mailed questionnaire in 1979, participants in a cancer-prevention programme using vitamin-A dietary supplements, and other sources. The majority of subjects were relatives and friends of ABA employees, and nearly half the cohort were either born at Wittenoom or first went there as children under 10 years of age. As most residents were at Wittenoom when the mine and mill were in operation during the period 1943 to 1966, 82% were first exposed to crocidolite 20 or more years ago. The proportion of other workers (i.e., not employed by ABA) and their families increased once the mining operations ceased. To date, 24 cases of mesothelioma have been reported in this cohort: 9 males and 15 females. Time from first exposure to diagnosis ranged from 23 to 44 years and residence in Wittenoom ranged from 6 weeks to 11 years.

Variability of the plateau response to methacholine in subjects without respiratory symptoms

BACKGROUND

Interpretation of measurements of limited maximal airway narrowing, or plateau response, requires knowledge of its variability within subjects and between methods.

METHODS

The repeatability of the plateau response to inhaled methacholine with a dosimeter (D) method (maximal dose 210 mumol) and a tidal breathing (T) method (730 mumol), and the agreement of the two methods, were measured in 16 subjects with mild or no asthma. Two tests by each method (D1,D2,T1,T2) were performed in random order over four consecutive days, with a third dosimeter (D3) test one week later. The dose producing a decrease in forced expiratory volume in one second (FEV1) of 10% (PD10) and the plateau were calculated from each dose-response curve.

RESULTS

A plateau was reached in all five tests in 12 subjects and in all tests except D3 in 14 subjects. PD10 was inversely related to the plateau (r = -0.95 for D, r = -0.77 for T). The 95% ranges for differences between two determinations of the plateau in a subject were +/- 11.9% (change in FEV1), +/- 19.2%, and +/- 20.3%, estimated from D1-2 and 1-3, and T1-2 tests, respectively. From the same tests the 95% ranges for the difference of a single determination from an individual's true mean value were +/- 8.3%, +/- 13.6%, and +/- 14.3%. The limits of agreement between methods indicated that 95% of the measurements of the plateau by tidal breathing ranged from 15.2% below to 13.3% above those obtained by dosimeter. There was no significant bias between methods. Tachyphylaxis over 24 hours occurred with PD10 but not with the plateau response.

CONCLUSIONS

The plateau response is a subject characteristic which is independent of the method of inhalation challenge testing. Repeatability of the plateau is low in this group of subjects with low airway responsiveness.

Effect of interferon-alpha 2a on malignant mesothelioma

Malignant mesothelioma (MM) is a tumor that is resistant to conventional therapy. Interferon-alpha (IFN-alpha) has been used in the treatment of some human tumors, and we have previously demonstrated an in vitro anti-proliferative effect of IFN against MM cell lines. Therefore, the effect of recombinant human IFN-alpha (IFN-alpha 2a) (Roferon-A, Hoffmann-La Roche) on previously untreated patients with MM has been studied. Twenty-five patients (24 male and 1 female), with a mean age of 59 +/- 9.9 years, were treated for 3 months with IFN-alpha 2a. The starting dose was 3 x 10(6) IU daily increasing to a maximum of 18 x 10(6) IU daily or as tolerated. All patients had measurable tumor on thoracic CT prior to commencement. CT scans were performed at 6 and 12 weeks to determine tumor response. Twenty patients completed 3 months of treatment. Five patients were withdrawn because of disease progression. Side effects were predictable and dose related. Dose reductions were necessary in 12 patients for grade 2 toxicity. One patient had a complete response (CR), 2 patients had partial responses (PR) (response rate = 12%), 13 (52%) patients remained stable, 1 of whom exhibited a delayed PR, and 9 (36%) had progressive disease. These data suggest that IFN-alpha 2a is well tolerated in patients with MM and is active against MM in a proportion of patients.

Nebuhaler versus wet aerosol for domiciliary bronchodilator therapy. A multi-centre clinical comparison

OBJECTIVE

To compare the clinical effectiveness and patient acceptance of a large spacer device (Nebuhaler) for delivery of metered dose aerosol (MDI) terbutaline with nebulised wet aerosol terbutaline.

DESIGN

Randomised open crossover study over two sequential four week treatment periods, following a two week run-in.

SETTING

Multi-centre including five adult thoracic units and three paediatric centres throughout Australia.

PATIENTS

Thirty-eight adults and 23 children with clinical asthma and reversible airflow obstruction (increase in forced expiratory volume in one second [FEV1] of greater than or equal to 15% in response to inhaled bronchodilator) entered the study proper. Six adults and one child withdrew.

INTERVENTIONS

Terbutaline was administered four times daily via Nebuhaler/MDI or nebuliser. Clinical assessment with spirometry and peak flow readings was made after run-in and at the end of each treatment period. Patients recorded on diary cards daily peak expiratory flow rates and symptom scores and comparisons of these results for each treatment period were made. At the completion of the study patients answered a treatment preference questionnaire.

RESULTS

No differences were found between the two treatment periods in diary card peak flow recordings and symptom score data, and in clinical assessment of spirometry and peak expiratory flow rates. There were also no differences between spirometry and peak flow values recorded at the clinic at randomisation and at the end of each treatment period, suggesting stable basal airflow obstruction over the period of the study. Thirty-two per cent of adults and 52% of children preferred the Nebuhaler/MDI combination, mainly because of convenience of use. Treatment preference was not related to any measured index of lung function.

CONCLUSIONS

MDI terbutaline delivered via Nebuhaler provides clinical benefit similar to that of wet aerosol terbutaline in the long-term domiciliary management of patients with stable airflow obstruction.

Risk factors for death in patients admitted to hospital with asthma: a follow-up study

Hospital records of patients with asthma admitted to teaching hospitals in Perth, Western Australia between 1976 and 1980 were examined retrospectively to identify characteristics of the illness which were associated with subsequent death. From 5722 admissions there were 195 deaths to December 1982, 186 of whom had records available (cases); 452 of the surviving subjects were used for comparison (controls). There was no difference in age of onset of asthma or cigarette smoking habits between the two groups, but ischaemic heart disease as an associated condition was significantly more frequent in cases. On admission to hospital an arterial PCO2 less than 45 mmHg was more frequent in those who died, but there were no differences in arterial PO2, lowest pH, highest or lowest FEV1 and FVC. Cases more frequently used home nebulisers and were more frequently prescribed corticosteroids, antibiotics and sedatives or tranquilizers prior to admission, corticosteroids and sedatives or tranquilisers during admission and sedatives or tranquilisers on discharge. These results suggest that cases had more severe asthma in that they were more often treated with home nebulisers, corticosteroids and antibiotics, but with the exception of PaCO2 the commonly used measurements of severity of asthma did not identify those at risk of death. The prescription of sedatives or tranquillisers appears to be associated with an increased risk of death in subjects with asthma.

Miliary spread of malignant pleural mesothelioma without a clinically identifiable pleural tumour

A 44-year-old man with past minor exposure to blue asbestos presented with supraclavicular lymphadenopathy and miliary shadowing on his chest radiograph. Cytology and electronmicroscopy on material obtained by fine needle aspiration from his cervical lymph node revealed malignant mesothelioma. Malignant mesothelioma cells were also present in bronchoalveolar lavage fluid and on transbronchial lung biopsy. At autopsy the right pleural cavity was studded with small tumour nodules. This case demonstrates that malignant mesothelioma may present as metastatic disease and without evidence on conventional investigations of a primary pleural tumour.

Relative risks of bronchial hyper-responsiveness associated with skin-prick test responses to common antigens in young adults

We studied 143 young subjects by skin-prick testing to common allergens and by the measurement of non-specific bronchial responsiveness (NSBR). A logistic regression model showed a prevalence odds ratio (POR) for bronchial hyper-responsiveness (PD20 less than 10 mumol methacholine) in house dust positive subjects of 4.10 (95% CI 1.77-9.51, P less than 0.001), and in mould positive subjects 5.72 (95% CI 2.06-15.9, P less than 0.001): the PORs for epithelia (2.05, P = 0.12) and grasses (1.78, P = 0.19) were not significant. If bronchial reactivity was assessed as measurable (PD20 less than 102 mumol methacholine) or not, the POR for house-dust-positive subjects was 4.83 (95% CI 2.23-10.5, P less than 0.001), for moulds was 10.5 (95% CI 2.33-47.5, P less than 0.001), for epithelia was 4.79 (95% CI 1.91-12.0, P less than 0.001), and for grasses was 2.21 (95% CI 1.11-4.4, P = 0.022). The results show the risk of bronchial hyper-responsiveness is greater in subjects sensitive to house dust and mould than in those reactive to grasses, and suggests that the presence or absence of increased NSBR in atopic individuals may depend on the antigens to which they become sensitized.

Smoking, exposure to crocidolite, and the incidence of lung cancer and asbestosis

In 1979 all former workers from the Wittenoom asbestos industry who could be traced to an address were sent a questionnaire to determine smoking history. Occupational exposure to crocidolite was known from employment records. Of 2928 questionnaires sent, satisfactory replies were received from 2400 men and 149 women. Eighty per cent of these had smoked at some time and 50% were still smoking. Since that time 40 cases of lung cancer and 66 cases of compensatable asbestosis have occurred in this cohort. The incidence of both lung cancer and asbestosis was greatest in those subjects with the highest levels of exposure to crocidolite and in ex-smokers. Statistical modelling of the joint effects of these exposures on the incidence of each disease indicated that crocidolite exposure multiplied the rates of lung cancer due to smoking and that smoking has no measurable effect on the rates of asbestosis. There was also some evidence that the incidence rate of lung cancer is falling with time.

Establishment and characterization of five human malignant mesothelioma cell lines derived from pleural effusions

Malignant mesothelioma (MM) is an aggressive tumour of the serosal cavities which is associated with exposure to asbestos. Studies of this tumour have been limited by a paucity of well-characterized human MM cell lines. In this study, 5 human MM cell lines were established from pleural effusions of patients with this malignancy. All 5 patients were males with known crocidolite asbestos exposure, who had received no treatment for their disease and in whom the diagnosis was confirmed by cytology, histology and electron microscopy (EM). These lines have been in culture from 11 to 25 months, and all of them for more than 18 passages. The appearance of the cells in culture was extremely varied; in 3 of the lines they were spindle-shaped with few vacuoles (JU77, LO68 and ONE58); in 1 line they had a thick, stellate shape with vacuoles (NO36) and in 1 they were very pleomorphic in both shape and size with irregular membranes and numerous vacuoles [DeH128 (M)]. Upon reaching confluence, cells in 3 of the 5 lines assumed the cobblestone-like pattern characteristic of epithelial-type cells, whereas in the other 2 (LO68 and ONE58) they remained spindle-shaped. All 5 lines demonstrated a loss of contact inhibition (i.e., piling) at confluence. Minimum doubling times varied significantly from 18 hr (JU77) to more than 30 hr [DeH128 (M)]. Cytological examination showed characteristic mesothelial/mesothelioma morphology, and epithelial membrane antigen (EMA) and cytokeratin were demonstrated in cells from all 5 lines. These cells lacked CEA and epithelial mucin. The presence of cell junctions, glycogen and numerous long, thin, branching microvilli was readily demonstrable by EM. All lines had abnormal karyotypes, with the modal chromosome number varying from 40 to 80. Variable chromosome numbers, numerous structural rearrangements and unrecognizable marker chromosomes were readily observed; however, the only consistent change seen was del 6q21 in 4 of the 5 lines. The establishment of these 5 cultured human MM cell lines now provides an opportunity for comparative study of several aspects of the biology of MM in vitro as well as screening new treatment modalities.

Computer quantitation of gallium 67 lung uptake in crocidolite (blue asbestos) workers of Western Australia

Pulmonary inflammation has been evaluated in 43 crocidolite-exposed asbestos (ASB) workers and 12 control subjects, using a quantitative index of gallium uptake (GI). The GI was compared with chest roentgenographs (CXRs) graded by the ILO classification. The ASB workers included 15 with asbestosis (CXR greater than or equal to 1/0), 19 with a normal CXR (CXR 0/0), and 9 with equivocal CXR changes (CXR 0/1). In individuals with asbestosis the GI was 3.6 +/- 0.3 (mean +/- SEM), P less than 0.01 compared with exposed patients without asbestosis. In exposed patients with equivocal CXR changes (0/1) the GI was 3.1 +/- 0.3, and in exposed patients with a normal CXR (0/0) the GI was 2.4 +/- 0.2. The GI for subjects without lung disease was 1.2 +/- 0.2, P less than 0.01 compared with exposed patients without asbestosis. The scans were scored independently by two observers, and the correlation coefficient of the two sets of GI was 0.95. These data demonstrate that subjects with crocidolite-induced asbestosis and exposed patients with equivocal CXR changes or a normal CXR have significantly increased GI.

Exposure to grain dust and changes in lung function

Respiratory symptoms and lung function were assessed in 41 seasonal grain handlers and related to duration of employment and level of exposure to grain dust. Ten public works department employees, not exposed to grain dust, were examined during the same period. Respiratory symptoms, forced expired volume in one second (FEV1), and bronchial responsiveness (dose of methacholine provoking a 20% fall in FEV1-PD20) were assessed before starting work and at weekly intervals during a period of employment lasting up to four weeks. Two atopic grainhandlers with pronounced bronchial hyperresponsiveness (PD20 less than 1 mumol) and a history of asthma withdrew from the study within two weeks because they developed severe asthma. Respiratory symptoms were more frequent and more often attributed to work in the grainhandlers than in the non-exposed subjects. In the grainhandlers the FEV1 decreased by a mean (95% confidence intervals) of 321 ml (198-444) (p less than 0.05) and the mean (95% confidence interval) PD20 decreased from 20.6 mumol (10.3-41.2) to 6.0 mumol (2.8-12.5) (p less than 0.05) after one week of work. Over the next three weeks the mean FEV1 returned towards the prestudy values. The mean PD20, however, remained significantly lower than the initial value. The mean FEV1 and PD20 did not change significantly in the non-exposed subjects. The frequency of symptoms and decreases in FEV1 were greater in grainhandlers when working in jobs where total exposure to dust was greater than 20 mg/m3 than when working in jobs where it was less than 10 mg/m3. The results indicate that occupational exposure to grain dust results in respiratory symptoms and changes in lung function, including increased airway responsiveness, within the first week of exposure to grain dust at work. These changes appear to be determined by the degree of dust exposure and suggest a direct effect of grain dust on the lung in these subjects.

Upper-limb and lower-limb exercise training in patients with chronic airflow obstruction

We designed a randomized controlled study to evaluate the benefit of upper-limb exercise training, alone and in combination with walking training, in patients with severe CAO. In an outpatient department supervised by a physiotherapist, we evaluated 28 patients with severe stable CAO (FEV1, 32 percent of predicted). Patients were randomly allocated to either a control (eight), upper-limb (six), lower-limb (seven), or combined (seven) exercise group. The upper-limb group trained with a circuit of upper-limb exercises, the lower-limb group by walking, and the combined group with both. Exercise was for one hour three times per week for eight weeks. Assessment before and after training included pulmonary function, mouth pressures, respiratory muscle endurance, maximal bicycle exercise test, maximal and submaximal arm ergometer, six-minute walking distance, and a scale of well-being (Bandura scale). Twenty-six patients completed the program. There was a significant improvement (Wilcoxon rank sum test) in the following: six-minute walking distance in the lower-limb (p less than 0.005) and combined (p less than 0.003) groups; arm ergometer in the upper-limb (p less than 0.005) and combined (p less than 0.04) groups; and the scale of well-being in the combined (p less than 0.005) group. There was no significant change in any other parameter measured. We conclude that exercise training improves exercise performance in severe CAO, that the training is specific for the muscle group trained, and that upper-limb exercises should be included in training programs for these patients.

Asbestos-induced release of a human alveolar macrophage-derived neutrophil chemotactic factor

Neutrophils accumulate in the alveoli of asbestos-exposed individuals. In determining whether asbestos fibers induce the release of neutrophil chemotactic factor (NCF) from human alveolar macrophages, alveolar macrophages (10(6) cell/mL) obtained by bronchoalveolar lavage from six non-asbestos-exposed control subjects were exposed to crocidolite (0.1 and 1 mg/mL), chrysotile (1 mg/mL), or medium alone for 4 h, and NCF activity was measured in the supernatants in a 48-well microchemotaxis chamber with polycarbonate membrane filters (pore size, 3 microns) and purified human neutrophils. Alveolar macrophages in medium alone released negligible amounts of NCF (4 +/- 1 neutrophils per high-power field [N/HPF]). When macrophages were exposed to crocidolite (0.1 and 1 mg/mL), significant NCF release occurred (43 +/- 9 and 105 +/- 32 N/HPF, respectively; p less than 0.01 for each amount compare to alveolar macrophages cultured in medium alone). Chrysotile (1 mg/mL) induced similar NCF release (96 +/- 14 N/HPF; p less than 0.01 compared to unstimulated alveolar macrophages). Partial characterization of the NCF by Sephadex G-25 fine gel filtration demonstrated a molecular size of less than 1,000 daltons. These results show that human alveolar macrophages release NCF after exposure to asbestos. Release of NCF by alveolar macrophages in asbestos-exposed individuals may play a central role in the pathogenesis of asbestosis.

Comparison of chest radiograph reading methods for assessing progress of pneumoconiosis over 10 years in Wittenoom crocidolite workers

Thirty three pairs of chest radiographs taken up to 10 years apart were obtained for 33 subjects suffering from asbestosis who had applied for compensation to the Pneumoconiosis Medical Board of Western Australia. Multiple films from the period before the first radiograph in each pair, from the intervening period between the two, and from the period subsequent to the second radiograph were also available and all films were read by two independent readers according to the 1980 ILO classification of pneumoconiosis. Films were read twice as side by side pairs ten years apart, twice as two separate randomly ordered films ten years apart, and once as part of the full series of all available chest radiographs on each subject to assess which method provided the best consistency (between reader variation) and repeatability (within reader variation). Judging by consistency, the full series method performed as well as either of the other methods when assessing radiographic changes and significantly better when assessing the level of profusion of small opacities. There was little to choose between the other two methods either judging by consistency or repeatability, which could not be estimated for the full series method. Use of all available films for a subject is recommended for assessing single films, as in a prevalence study, as well as for documenting change in a longitudinal study.

Predictions of future cases of asbestos-related disease among former miners and millers of crocidolite in Western Australia

In a cohort of 6502 male and 410 female former workers from the crocidolite (blue asbestos) mining and milling works at Wittenoom, Western Australia, there were 94 cases of malignant mesothelioma (12 cases of peritoneal mesothelioma), 141 cases of lung cancer and 356 successful compensation claims for asbestosis to the end of 1986. After adjusting for measured covariate effects by means of proportional hazards regression analysis, smooth curves were fitted to the resulting "underlying" incidence rates for malignant mesothelioma, lung cancer and asbestosis, separately, and for mortality of any cause. By the use of these curves and individual risk estimates, predictions have been made of the future incidence of these diseases to the year 2020. With the assumption that all subjects who were not known to be dead or departed overseas still were alive at December 31, 1986, and excluding persons of more than 85 years of age, the number of new cases of mesothelioma is expected to rise to a peak of around 25 cases per year in 2010, with an expected total number of 692 cases of mesothelioma (95% confidence interval [CI], 394-990 cases) between 1987 and 2020. A total of 2898 deaths (95% CI, 2284-3511 deaths) of any cause is expected in the same period. New cases of lung cancer and asbestosis are expected to continue at roughly the current rates of eight and 17 cases per year, respectively, before declining after the year 2000, leading to totals of 183 cases (95% CI, 34-335 cases) and 482 cases (95% CI, 236-728 cases), respectively, being expected by the year 2020. Predictions that were based on the censoring of subjects at the date that they last were known to be alive resulted in slightly higher, but probably less accurate, estimates.

Indomethacin augments lymphokine-activated killer cell generation by patients with malignant mesothelioma

Human malignant mesothelioma (MM) cells are resistant to natural killer (NK) cell lysis but susceptible to lysis by lymphokine-activated killer (LAK) cells from control individuals. The present study was performed to determine the capacity of patients with MM (n = 22) and individuals occupationally exposed to asbestos (the major population at risk of developing this disease, n = 52) to generate LAK cells capable of effectively lysing human mesothelioma cells. Compared to controls (n = 20), both patient groups demonstrated significantly depressed LAK cell activity against mesothelioma tumor cell targets (55 +/- 3% lysis by controls vs 34 +/- 3% lysis by patients with MM, P less than 0.005; and 45 +/- 3% lysis by asbestos-exposed individuals, P less than 0.025). Addition of 10 micrograms/ml indomethacin during LAK cell generation restored normal LAK cell activity for patients with MM (52 +/- 6% lysis of cultured human MM cells, P = NS compared to controls), suggesting that the defective cytolytic cell function observed in some patients with MM is a result of prostaglandin-induced immunosuppression. The ability of indomethacin to restore suppressed LAK cell activity in patients with MM suggests that the concomitant use of this agent in ex vivo LAK cell generation and in patients undergoing interleukin/LAK cell therapy may be beneficial.

Respiratory symptoms, lung function, and sensitisation to flour in a British bakery

A survey of dust exposure, respiratory symptoms, lung function, and response to skin prick tests was conducted in a modern British bakery. Of the 318 bakery employees, 279 (88%) took part. Jobs were ranked from 0 to 10 by perceived dustiness and this ranking correlated well with total dust concentration measured in 79 personal dust samples. Nine samples had concentrations greater than 10 mg/m3, the exposure limit for nuisance dust. All participants completed a self administered questionnaire on symptoms and their relation to work. FEV1 and FVC were measured by a dry wedge spirometer and bronchial reactivity to methacholine was estimated. Skin prick tests were performed with three common allergens and with 11 allergens likely to be found in bakery dust, including mites and moulds. Of the participants in the main exposure group, 35% reported chest symptoms which in 13% were work related. The corresponding figures for nasal symptoms were 38% and 19%. Symptoms, lung function, bronchial reactivity, and response to skin prick tests were related to current or past exposure to dust using logistic or linear regression analysis as appropriate. Exposure rank was significantly associated with most of the response variables studied. The study shows that respiratory symptoms and sensitisation are common, even in a modern bakery.

Cancer mortality in relation to measures of occupational exposure to crocidolite at Wittenoom Gorge in Western Australia

The separate and combined effects of duration and intensity of exposure to crocidolite on mortality from lung cancer, malignant mesothelioma, and stomach cancer were examined in 6506 male former crocidolite miners and millers at Wittenoom Gorge, Western Australia. Each subject who had died from lung cancer (92), mesothelioma (31), or stomach cancer (17) was matched with up to 20 control subjects of the same age who were not known to have died before the index subject. Relations of dose and time of exposure to crocidolite to risk of death were modelled by conditional logistic regression. For lung cancer, the best fitting multiplicative model was one which estimated a relative risk (RR) of 1.12 (95% CI 1.04-1.20) per year of exposure and 1.01 (95% CI 1.00-1.01) per fibre/ml. This was statistically indistinguishable from an additive model showing an increase in RR of 0.01045 (95% CI 0.008-0.020) per f/ml year. For mesothelioma the best fitting model appeared to be one estimating a RR of 24.9 (95% CI 3.51-1.77) per log year since first exposed and a RR of 10.5 (95% CI 3.12-35.1) if exposed for longer than six months. This was not distinguishable statistically from a model that showed mortality increasing as the fourth power of time since first exposed less the fourth power of time since last exposed. The effect of intensity of exposure on the RR for mesothelioma was only slight. There was no consistent effect of any measure of exposure to crocidolite on death from stomach cancer.

Natural history of pleural thickening after exposure to crocidolite

Serial plain chest radiographs of 384 men who worked at the Wittenoom crocidolite mine and mill between 1943 and 1966 and who applied for pneumoconiosis compensation between 1948 and 1982 have been examined independently by two trained observers for pleural disease using the 1980 ILO-UICC classification of radiographs to record width and extent of pleural disease. Radiographs covering follow up periods of from two to 38 years were examined (median number of films per subject was nine). The degree of crocidolite exposure was estimated from employment records and a survey of airborne fibre concentrations performed in 1966. Agreement between the observers on the presence and degree of pleural disease in the final film for each subject was moderately close (Kendall's tau B = 0.62) and was least for subjects with thickening less than 5 mm in width. Diffuse pleural thickening extending for greater than 50% of the lateral chest wall was the most common type recorded by both observers. Minor pleural thickening frequently progressed in extent along the lateral chest wall but progression beyond 5 mm in thickness was less common. Pleural plaques were not seen to progress beyond their initial thickness or extent. The rate of onset of thickening in this population increased continually from the time of first exposure and also increased slightly with age. There was evidence that the level of total cumulative exposure to crocidolite increased the rate of onset of pleural thickening in the period between five and 15 years after first exposure. Rate of progression of established thickening was greatest in subjects who first developed thickening early after first exposure. The relative rate of progression decreased slowly with time from first signs of thickening and there was no evidence of any progression more than 15 years after onset.

Gallium lung scanning and bronchoalveolar lavage in crocidolite-exposed workers

Gallium lung scanning is widely used to evaluate pulmonary inflammation in patients with interstitial lung disease but has not previously been reported in crocidolite-exposed workers. In order to characterize the pulmonary inflammation caused by crocidolite inhalation, GLS and BAL findings were related to chest x-ray film changes graded according to the ILO classification of roentgenograms of pneumoconioses. In individuals with roentgenographic evidence of asbestosis (CXR greater than or equal to 1/0, n = 15), 13 had a positive GLS and 13 had an abnormal BAL. In asbestos-exposed individuals with equivocal chest x-ray film changes (CXR 0/1, n = 12), six had a positive GLS and six had BAL changes (both GLS and BAL abnormal in three). In individuals with a normal chest x-ray film (CXR 0/0 n = 8), two had a positive GLS and two BAL changes (both abnormal in 1). These data demonstrate that most subjects with crocidolite-induced asbestosis have an abnormal GLS and BAL. In addition, many individuals with asbestos exposure and equivocal or no chest x-ray film changes have an abnormal GLS and/or BAL, suggesting the presence of active subclinical pulmonary inflammation in these individuals.