A respiratory epidemiological study of stevedores intermittently exposed to asbestos in a South African port

Our plain-English summary of A respiratory epidemiological study of stevedores intermittently exposed to asbestos in a South African port, by J.E. Myers, D. Garisch, H.S. Myers, et al (American Journal of Industrial Medicine, 1985).

The study

• Authors: J.E. Myers, D. Garisch, H.S. Myers, J.E. Cornell, R.D. Rwexu
• Journal: American Journal of Industrial Medicine
• Published: 1985;7(4):273-83
• Cited by: 19 articles, as counted by NIH iCite
• Read it: PubMed · Publisher
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 001214).

Abstract

The prevalence of asbestosis in stevedores intermittently transporting crocidolite asbestos in a South African port was found to be 30% in a cross-sectional survey. Diagnostic criteria are discussed in terms of the low index of suspicion for industrial diseases, the high probability of missing slight radiological changes, and the attribution of radiological lesions to other diseases, particularly tuberculosis, in a high prevalence area. Results are compared with other studies. Asbestosis was not associated with tuberculosis. Smoking was not significantly associated with asbestosis, other respiratory signs and symptoms, or radiological abnormality.

In plain English

This cross-sectional survey, carried out in March 1982, studied stevedores in Port Elizabeth, South Africa, who loaded crocidolite asbestos, on average two cargoes a month. Of 324 stevedores, all African men, 203 were analysed. Most of the others were excluded for previous dusty jobs or poor-quality X-rays or breathing tests. Asbestosis was defined by chest X-ray as small-opacity profusion of 4(1/0) or more on the ILO 12-point scale. By that definition it was found in 61 workers (30%): 19% of those with 15 years' exposure or less and 40.4% of those with more than 15 years of service. Pleural abnormalities appeared on 29.6% of X-rays. Lung capacity (FVC) was below 80% of predicted in 37%, and this became more common as X-ray changes increased. FVC fell faster with age than in a comparison group of textile workers. Asbestosis was not significantly linked with smoking or tuberculosis. The original local X-ray reports had found no asbestosis. The authors noted that readers agreed least in the borderline X-ray categories.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Cross-sectional prevalence survey (questionnaire, physical examination, spirometry, chest radiographs), with comparison of lung function decline against a group of cotton textile workers
• Who was studied: 324 stevedores (the whole workforce except ten men on holiday) in Port Elizabeth, South Africa, surveyed in March 1982. All were African males. 121 were excluded, leaving 203 in the analysis, with a mean age of 45 years and mean service of 19 years.
• Exposure: Intermittent exposure to crocidolite asbestos mined in the North Western Cape, loaded at the port on average two cargoes per month. Bags were often damaged, and the holds were very dusty during loading.
• Main results:
  • Asbestosis (radiological profusion category 4(1/0) or more) was diagnosed in 61 of the 203 stevedores (30%).
  • Among the 203 stevedores, 20% had a profusion category of 5(1/1) or more.
  • Asbestosis prevalence was 19% in stevedores with 15 years' exposure or less and 40.4% in those with more than 15 years of service. The relative risk for the longer-service group was 2.85, which the authors called highly significant (p = .001).
  • In regression analysis of the stevedores, only age, not length of service, was a significant predictor of profusion.
  • Pleural abnormalities were seen in 60 radiographs (29.6%). Half of these (30, or 14.8%) also had parenchymal opacities of category 4 or more.
  • 37% of the stevedores had FVC below 80% of predicted. The mean FVC was 83.17% of predicted.
  • In contingency table analysis, FVC abnormality became more common with longer service (p less than .05). Relative risks were 1.95 for 10 to 20 years and 2.1 for more than 20 years. Length of service did not contribute in the regression analysis.
  • FVC abnormality rose with X-ray profusion category: 30% in category 2 and 90% in combined categories 7 to 9 (test for trend p less than .01).
  • Height-adjusted FVC declined with age significantly faster in the stevedores (slope -.0316) than in 499 African male cotton textile workers from non-dusty departments (slope -.0229), p less than .05.
  • Smokers and non-smokers did not differ significantly in asthma symptoms, chronic bronchitis symptoms, dyspnoea or FVC measures. Non-smokers had a higher adjusted mean profusion (3.64) than smokers (3.15), but this was not significant (p = .11).
  • Past or present tuberculosis was found in 16.2% of the stevedores. After age standardisation, those with and without asbestosis did not differ significantly in tuberculosis, smoking history or lung function.
  • The initial X-ray reports had found no cases of asbestosis. The authors found that many of the more obvious lesions had been misdiagnosed as tuberculosis.
• The authors' conclusion: The authors concluded that the significant link between increasing profusion of small opacities and FVC abnormality tended to cross-validate both as indices of asbestos-related abnormality. They also said that the radiological diagnosis of asbestosis is often difficult, with slight changes missed and lesions attributed to tuberculosis.
• Limitations the authors state:
  • The authors recognised that the spirographic and radiographic abnormalities could have other causes.
  • Agreement between X-ray readers was low in the borderline categories 3(0/1) and 4(1/0).
  • The low prevalence of crepitations may have been a false-negative finding, because the examinations were done in noisy worksite conditions.
  • Comparison with other studies may be difficult and of doubtful value, because of differences in diagnostic criteria, exposure and time since first exposure.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Asbestosis.

Medical terms in this study, explained in our Lexicon: Crocidolite, Attribution.

Related studies

• Asbestosis in South African asbestos miners — G.K. Sluis-Cremer (1970)
• Radiologic abnormalities in South African mica millers: a survey of a mica milling plant in the Limpopo Province — E. Venter, B. Nyantumbu, et al. (2004)
• Asbestos and asbestos-related disease: the South African case — J.E. Myers, J. Aron, et al. (1987)
• Lung cancer, tobacco, and environmental factors in the African population of the Northern Province, South Africa — O. Mzileni, F. Sitas, et al. (1999)
• Risk of mesothelioma from exposure to crocidolite asbestos: a 1995 update of a South African mortality study — D. Kielkowski, G. Nelson, et al. (2000)
• South African asbestos: production, exports, and destinations, 1959-1993 — J.S. Harington, N.D. McGlashan (1998)

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