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.     

Maximal airway narrowing in a general population.

To characterize airway responses in a population sample, respiratory symptoms, smoking habits, and changes in FEV1 (delta FEV1) to inhaled methacholine (maximal cumulative dose of 196 mumol or maximal decrease in FEV1 of 50%) were recorded in 201 subjects. From each dose-response curve the plateau (delta FEV1 less than or equal to 5% over two or more dose steps) response, the maximal response (average of responses on the plateau or maximal delta FEV1 when no plateau was present), slope, and PD20 (dose required to cause delta FEV1 greater than 20%) were derived. The pattern of dose-response curves was a continuous change from being flat (maximal delta FEV1 less than or equal to 5%), becoming steeper with a plateau that occurred at a greater change in FEV1 as the curves were shifted more to the left, to being the steepest without a plateau response. Maximal delta FEV1 was significantly related to the PD20 (r = -0.64, p less than 0.001) and the slope (r = 0.63, p less than 0.001). A history of doctor-diagnosed asthma or wheeze in the last 12 months was related to the level of the maximal delta FEV1 and to PD20. Likelihood ratios [LR = sensitivity/(1-specificity)] for asthma or wheeze were higher for a maximal delta FEV1 of 50% plus a PD20 of 4 mumol (LR = 6.5) or 1 mumol (LR = 7) than for either alone. Subjects without reported asthma or wheeze more often had a plateau on the dose-response curve (76%) than those with a positive history (49%, p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)     

SPUTUM ASBESTOS BODIES AND RADIOGRAPHIC CHANGES IN RESIDENTS OF WITTENOOM,WESTERN AUSTRALIA

Sputum was collected for examination for asbestos bodies from residents in Wittenoom Gorge in December 1980. The chest radiographs of Wittenoom residents who had participated voluntarily in a radiological survey in July 1980 were examined for evidence of asbestos-induced pleural or parenchymal disease which may have resulted from environmental exposure to crocidolite. The results indicate no measurable health effect of previous environmental exposure of current residents. However as there are serious limitations in the methods for indicating the level of past asbestos exposure and the size of the township has declined markedly in recent years with changing population structure, this study does not exclude the presence of an environmental health hazard. The ultimate measure of effect will depend on continuing surveillance of ex-residents for deaths from malignant disease.     

Accelerated loss of FEV- in polyurethane production workers: a four-year prospective study

A four-year longitudinal study of ventilatory function in polyurethane-foam production workers exposed to toluene diisocyanate (TDI) revealed a dose-response relationship between average exposure to TDI and change in forced expiratory volume per second (FEV-1). Workers with mean exposure in excess of 0.0035 ppm showed a greater rate of decline of FEV-1 over the four-year period than that expected from aging. Factors other than TDI exposure (sex, smoking history, history of atopy) do not account for the loss. The current threshold limit value (TLV) for exposure to TDI in industry (0.02 ppm) does not protect workers from accelerated impairment of ventilatory capacity.     

Loss of pulmonary elastic recoil in workers formerly exposed to proteolytic enzyme (alcalase) in the detergent industry.

Sixty-seven workers in the detergent industry whose exposure to proteolytic enzyme ceased in 1969 have been examined clinically and functionally. By comparison with 42 lightly and moderately exposed subjects, 13 heavily exposed subjects showed significant loss of pulmonary elastic recoil as evidenced by increased lung volumes and increased pulmonary compliance, but there were no differences in airways resistance or other parameters of lung function. No difference was found between the two groups in relation to symptoms on exposure, current exercise tolerance, skin reactivity to the proteolytic enzyme alcalase, trypsin inhibitor capacity, and other features. An increased clinical grade of breathlessness was associated with evidence of airways obstruction, but not of altered elastic recoil. Comparison of the data on lung mechanics with results obtained in 1970 suggests that partial recovery of pulmonary elastic recoil may have occurred in some cases. It is also suggested that diminished elastic recoil, in the absence of impairment of transfer factor at rest, may reflect altered physical properties of the lung fibre network without loss of effective surface area available for gas exchange.     

Superficial- and deep-tissue temperature increases in anesthetized dogs during exposure to high specific absorption rates in a 1.5-T MR imager

Superficial- and deep-tissue heating was measured in five dogs during high-specific-absorption-rate radiofrequency (RF) irradiation to see whether significant temperature changes could be produced by a 1.5-T clinical magnetic resonance imager. The RF power output employed was 6.3 times that required for routine imaging. Temperature probes were placed in both deep and superficial tissues, and temperatures were recorded before, during, and after exposure. In each dog, there was a linear temperature increase of several degrees during RF exposure; the maximal average change was 4.6 degrees C in the urinary bladder. The temperature increase was slightly greater in deep tissues than in superficial tissues. The calculated specific absorption rate, based on the temperature change, averaged 7.9 W/kg for all five dogs. These findings argue for continued caution in the design and operation of imagers capable of high specific absorption rates, particularly when they are used for imaging infants or patients with altered thermoregulatory capability.     

The risk of lung cancer with increasing time since ceasing exposure to asbestos and quitting smoking

Objectives

To examine if the risk of lung cancer declines with increasing time since ceasing exposure to asbestos and quitting smoking, and to determine the relative asbestos effect between non‐smokers and current smokers.

Methods

A cohort study of 2935 former workers of the crocidolite mine and mill at Wittenoom, who responded to a questionnaire on smoking first issued in 1979 and on whom quantitative estimates of asbestos exposure are known. Conditional logistic regression was used to relate asbestos exposure, smoking category, and risk of lung cancer.

Results

Eighteen per cent of the cohort reported never smoking; 66% of cases and 50% of non‐cases were current smokers. Past smokers who ceased smoking within six years of the survey (OR = 22.1, 95% CI 5.6 to 87.0), those who ceased smoking 20 or more years before the survey (OR = 1.9, 95% CI 0.50 to 7.2), and current smokers (<20 cigarettes per day (OR = 6.8, 95% CI 2.0 to 22.7) or >20 cigarettes per day (OR = 13.2, 95% CI 4.1 to 42.5)) had higher risks of lung cancer compared to never smokers after adjusting for asbestos exposure and age. The asbestos effect between non‐smokers and current smokers was 1.23 (95% CI 0.35 to 4.32).

Conclusion

Persons exposed to asbestos and tobacco but who subsequently quit, remain at an increased risk for lung cancer up to 20 years after smoking cessation, compared to never smokers. Although the relative risk of lung cancer appears higher in never and ex‐smokers than in current smokers, those who both smoke and have been exposed to asbestos have the highest risk; this study emphasises the importance of smoking prevention and smoking cessation programmes within this high risk cohort.     

Chemical countermeasures for the control of bacterial biofilms: effective compounds and promising targets

The pathogenic nature of many infectious bacteria is enhanced by their ability to form surface-associated, protected communities known as "biofilms." Due to various factors, bacteria in biofilm communities display significantly greater resistance to traditional antimicrobial therapies than their planktonic brethren. This resistance complicates many common bacterial infections, resulting in recurrent ear infections, bacterial endocarditis, chronic lung infection in cystic fibrosis, infectious kidney stones, and surface infection of implanted medical devices. Owing to the serious nature of many biofilm-mediated infections and the near-complete dearth of effective strategies for treating them, efforts are underway to further understand the nature of bacterial infections involving biofilms and to discover and develop effective therapies to combat them. Particularly, several classes of chemical compounds have shown promise in combating biofilms when used in conjunction with traditional antimicrobials. The vast majority of these compounds exert their anti-biofilm properties through disruption of "quorum sensing," a common means of intercellular communication in bacterial communities that allows coordinated expression of virulence factors and facilitates formation of the oft-complex architecture of mature bacterial biofilms. Other new chemical entities are effective against biofilms without necessarily affecting quorum sensing. This review summarizes salient research in the development of effective chemical countermeasures for Gram-negative and Gram-positive bacterial infections involving biofilms.