Lung and pleural fibrosis in asbestos-exposed workers: a risk factor for pneumonia mortality

Our plain-English summary of Lung and pleural fibrosis in asbestos-exposed workers: a risk factor for pneumonia mortality, by T. Vehmas, P. Pallasaho, P. Oksa (Epidemiology and Infection, 2012).

The study

• Authors: T. Vehmas, P. Pallasaho, P. Oksa
• Journal: Epidemiology and Infection
• Published: 2012;140(11):1987-92
• Cited by: 5 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Lungs exposed to occupational dust may be especially vulnerable to fatal infections. We followed up asbestos-exposed workers (n=590) originally screened for lung cancer with computed tomography and scored for pleuropulmonary fibrosis. We checked these workers' influenza and pneumonia mortality data (ICD-10 codes J10-J18) in the national register. In total, 191 deaths, including 43 deaths from infectious pneumonia, occurred in 6158 person-years of follow-up (mean follow-up time 10·44 years). 'Some interstitial fibrosis' [hazard ratio (HR) 2·26, 95% confidence interval (CI) 0·98-5·19, P=0·06] and 'definite interstitial fibrosis' (HR 3·70, 95% CI 1·22-11·23, P=0·02) were associated with an increased risk of death from pneumonia compared to no fibrosis. Asbestosis patients, i.e. those with both asbestos exposure and lung fibrosis, therefore appear to be particularly at risk for death from pneumonia. These patients should be vaccinated against influenza and Pneumococcus.

In plain English

This Finnish study asked whether lung and pleural fibrosis (scarring) on CT was linked to later pneumonia death in asbestos-exposed workers. It included 590 construction workers (580 men, 10 women) from the Helsinki area screened for lung cancer by CT in 1996 to 1997. Based on three radiologists' scores, workers were grouped as no fibrosis (197), some fibrosis (344) or definite fibrosis (49). In Finland, definite fibrosis is considered sufficient for an asbestosis diagnosis given adequate work history. Deaths were traced in the national register to 2007, partly to 2009. Of 191 deaths, 43 were from pneumonia: 3.6% of the no-fibrosis, 8.7% of the some-fibrosis and 12.2% of the definite-fibrosis group. In 41, pneumonia was the immediate cause, with another disease underlying. Adjusted for age and smoking, and compared with no fibrosis, the hazard ratio was 2.26 (95% CI 0.98 to 5.19, P=0.06, not statistically significant) for some fibrosis and 3.70 (95% CI 1.22 to 11.23, P=0.02) for definite fibrosis. Years of asbestos exposure had no significant effect. The authors concluded these fibrotic changes were a risk factor for death from pneumonia.

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: Follow-up (cohort) study of a previously CT-screened group, linked to the national cause-of-death register, analysed with Cox regression adjusted for age and pack-years of smoking
• Who was studied: 590 asbestos-exposed construction workers (580 men, 10 women) living in the Helsinki area, Finland. They were screened for lung cancer by high-resolution CT in 1996 to 1997. Follow-up was comprehensive to the end of 2007 and partial to 13 April 2009 (mean follow-up 10.44 years, 6158 person-years). Mean age at CT was 63 years. By CT fibrosis score they were grouped as no fibrosis (n=197), some fibrosis (n=344) and definite fibrosis (n=49). Smoking of at least 10 pack-years was required for those without an asbestosis diagnosis.
• Exposure: Occupational asbestos exposure in construction work. Fiber types are not specified. Exposure was measured only as years of exposure (mean 26 years, range 2 to 48 years). The main factor studied was the degree of lung and pleural fibrosis on CT.
• Main results:
  • Among the 590 workers there were 191 deaths. 43 workers died of pneumonia (43/590, 7.3%), which was 22.5% (43/191) of all deaths.
  • Of the 43 pneumonia deaths, pneumonia was the underlying cause of death in 2. In the other 41 it was the immediate cause, with another disease as the underlying cause: 7 cardiovascular, 16 cancer (9 of them lung cancer), 8 respiratory (5 asbestosis, 3 COPD) and 10 other.
  • Pneumonia deaths by fibrosis group: 7/197 (3.6%) with no fibrosis, 30/344 (8.7%) with some fibrosis, 6/49 (12.2%) with definite fibrosis.
  • Compared with no fibrosis, and adjusted for age and pack-years, definite interstitial fibrosis had a hazard ratio of 3.70 (95% CI 1.22 to 11.23, P=0.02).
  • Compared with no fibrosis, some interstitial fibrosis had a hazard ratio of 2.26 (95% CI 0.98 to 5.19, P=0.06). This is above the study's significance threshold of P less than 0.05.
  • Increasing age was also positively associated with pneumonia death (HR 1.06, 95% CI 1.01 to 1.12, per Table 2).
  • Years of asbestos exposure had no significant effect on pneumonia death.
  • When individual CT signs were studied separately, several emerged as significant predictors of pneumonia death: subpleural perpendicular lines, parenchymal bands, subpleural nodules, honeycombing and the extent of pleural plaques.
  • The authors described the effect of pleural plaques on pneumonia mortality as statistically significant but minor (extent of plaques HR 1.006, 95% CI 1.001 to 1.012, per Table 3).
• The authors' conclusion: The authors concluded that pleuropulmonary fibrotic changes were a risk factor for death from pneumonia in asbestos-exposed workers. In their view, asbestosis patients (those with both asbestos exposure and lung fibrosis) appear to be particularly at risk. They also stated that these workers should be vaccinated against influenza and Pneumococcus.
• Limitations the authors state:
  • Agreement between the radiologists on fibrotic signs was limited: intraclass correlations between observers ranged from 0.20 to 0.64.
  • About the first 20 patients were imaged with fewer CT slices, which may have caused minor misclassification.
  • Whether a few individuals were alive or dead in 2009 remains uncertain.
  • All subjects were asbestos-exposed, which may dilute the effects found. The authors stated that the risks are therefore likely to be underestimates.
  • Exposure was quantified only as years of exposure, because the workers had several lifetime tasks and exposures that are difficult to evaluate.
  • Smoking did not significantly raise the risk of pneumonia death. The authors attributed this to selection bias, because smoking was an inclusion criterion only for those without a previous asbestosis diagnosis.

Topics

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

Medical terms in this study, explained in our Lexicon: Fibrosis, Lung Cancer, Interstitial Fibrosis, Hazard Ratio, confidence interval, Asbestos Exposure.

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