Factors influencing the reading of small irregular opacities in a radiological survey of asbestos miners in South Africa

Our plain-English summary of Factors influencing the reading of small irregular opacities in a radiological survey of asbestos miners in South Africa, by G.K. Sluis-Cremer, P.A. Hessel, E. Hnizdo (Archives of Environmental Health, 1989).

The study

• Authors: G.K. Sluis-Cremer, P.A. Hessel, E. Hnizdo
• Journal: Archives of Environmental Health
• Published: 1989;44(4):237-43
• Cited by: 10 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. 000161).

Abstract

A cross-sectional radiological survey of 2,245 men who were employed in South African asbestos mines was conducted in 1976. Since 1976, the lungs of 172 of these men who died have been examined to establish the presence of asbestosis or other pneumoconiosis. The x-ray readings (ILO/UC 1971) were compared with the pathological findings. A high prevalence of false positive readings, particularly for two of the three readers, was found. False negative readings were also very prevalent. Detailed information about asbestos and other mining exposure, smoking habit, age, height, and weight were examined to determine what influence they may have had in inducing false positive findings. Other dust exposure and smoking appeared to be possible factors, whereas age and obesity were probably not. It is suggested that the term "small irregular opacities" requires more precise definition.

In plain English

In a 1976 survey, three readers independently and blindly classified chest x-rays of 2,245 Caucasian or mixed-race men employed in South African asbestos mines, mostly crocidolite and amosite mines. Many had also worked in gold mines with silica-containing dust. The authors compared these readings with autopsy lung examinations of 172 men who later died. Of 105 men without asbestosis at autopsy, reader 1 had read small irregular opacities (category 1/0 or more) in 25 (23.8%) and reader 3 in 21 (20.0%). Reader 2 had few such false positives but the most false negatives. Of 42 x-rays where two of three readers agreed on 1/0 or more, 12 (28%) showed no asbestosis. False-positive cases had little asbestos exposure but high gold-mine dust exposure. The authors judged that smoking appeared to influence readings, although the differences were not statistically significant. Body mass index showed only very small, nonsignificant differences between groups. X-rays preceded death by 5.7 years on average. The authors concluded that a 1/0 or higher reading, even with two-reader agreement, should not be equated with asbestosis.

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: Comparison of chest x-ray readings (ILO/UC 1971 classification) from a cross-sectional radiological survey with later autopsy lung findings, which were used as the standard of comparison
• Who was studied: 2,245 Caucasian or mixed-race males employed in South African asbestos mines, surveyed radiologically in 1976 (films taken between November 1970 and November 1975). The cardiorespiratory organs of 172 of these men who later died were examined at the Medical Bureau for Occupational Diseases.
• Exposure: Asbestos mining, mostly in amphibole (crocidolite and amosite) mines, measured as years of exposure and as cumulative exposure in fiber/mL-years. Many men had also worked in gold mines with dust containing about 30% free crystalline silica, measured in quartz equivalent particle-years. Smoking, age and body mass index were also examined.
• Main results:
  • Among the 105 men with no asbestosis at autopsy, reader 1 had read small irregular opacities (category 1/0 or more) in 25 (23.8%) and reader 3 in 21 (20.0%).
  • Reader 2 had very few false positive readings (5 of 172) but the largest number of false negatives: 41 of 172 x-rays read 0/0 in men who had asbestosis at autopsy. The comparable false negative counts were 23 for reader 1 and 28 for reader 3.
  • Of 42 x-rays on which two of the three readers agreed on category 1/0 or more, 12 (28%) had no asbestosis at autopsy.
  • Men with false positive readings had very little asbestos dust exposure.
  • Men with false positive readings had high dust exposure in gold mines, for all three readers.
  • Among men without asbestosis at autopsy, the authors compared those with silicosis (N = 26) and those without (N = 81). Reader 1 read opacities in 26.9% versus 22.2%, and reader 3 in 23.1% versus 18.5%. Neither difference was statistically significant.
  • Men read as 0/1 or greater who had no asbestosis at autopsy had equal or higher median tobacco consumption than men with true positive or true negative readings. These differences were not statistically significant.
  • Mean daily cigarette consumption did not differ significantly between men with asbestosis at autopsy (14.9 per day) and men without it (16.2 per day).
  • Average body mass index showed very small, nonsignificant differences between the outcome groups. The authors found no indication that obesity affected the readings.
  • The odds ratios for the association between a reading of 1/0 or more and slight asbestosis at autopsy were 2.4 (p = .02) for reader 1, 5.53 (p = .004) for reader 2, and 2.61 (p = .017) for reader 3.
  • The authors wrote that the false positive group was significantly older than the true negative group for all readers. However, the age table marks this difference as significant (p less than .05) only for readers 1 and 3. The authors said an independent effect of age could not be excluded.
• The authors' conclusion: The authors concluded that a reading of small irregular opacities of category 1/0 or more, even when two of three readers agree, should not be equated with interstitial fibrosis or asbestosis. They also concluded that the definition of small irregular opacities should be refined.
• Limitations the authors state:
  • The x-rays were taken an average of 5.7 years before death, so asbestosis may have developed after the x-ray. The numbers of false negatives and true positives may therefore have been overestimated.
  • The 172 autopsied men represented the early deaths, so their findings may not reflect the whole cohort.
  • Smoking was measured only as cigarettes per day at the time of the x-ray. Pack-years would have been a more sensitive measure.

Topics

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

Medical terms in this study, explained in our Lexicon: Pneumoconiosis, Habit.

Related studies

• Progression of irregular opacities in asbestos miners — G.K. Sluis-Cremer, E. Hnizdo (1989)
• The mortality of amphibole miners in South Africa, 1946-80 — G.K. Sluis-Cremer, F.D. Liddell, et al. (1992)
• Effect of tobacco smoking on the presence of asbestosis at postmortem and on the reading of irregular opacities on roentgenograms in asbestos-exposed workers — E. Hnizdo, G.K. Sluis-Cremer (1988)
• Effect of tobacco smoking on the presence of asbestosis at postmortem and on the reading of irregular opacities on roentgenograms in asbestos-exposed workers — A. Kraut, J. Godbold, et al. (1989)
• Cigarette smoking and small irregular opacities — W. Weiss (1991)
• Thickening of pulmonary interlobar fissures: exposure-response relationship in crocidolite and amosite miners — A. Solomon, L.M. Irwig, et al. (1979)

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