Overstating the consequences: Peipins et al.'s response.

Flynn et al. raise concerns about differences in chest radiograph interpretation and bias among B-readers in our study (Peipins et al. 2003). Furthermore, they suggest that an internal review by Health Network America (HNA) found misdiagnosis in many cases, with subpleural fat being miscoded as asbestos-related pleural changes.

In the Libby, Montana, screening program, all films were reviewed by at least two experienced B-readers, with a third B-reader functioning as a "tiebreaker" to settle disagreements. Participants were categorized as "positive" if two B-readers reported any pleural abnormality, and as "indeterminate" if only one B-reader reported an abnormality. For clinical purposes, participants in both the "positive" and the "indeterminate" categories were notified and encouraged to follow up with their personal physician. The three B-readers are respected experts in the field and are distinguished members of academic institutions. Furthermore, the design of the screening program employed is similar to that used in previous studies of asbestos-related radiographic abnormalities (Rogan et al. 1987, 2000).

Although the B-readers in the screening program were aware that the X rays were from the Libby area, they had no other information about occupational or environmental exposure pathways and were blinded to the identities of individuals who were screened. This is important because a clear exposure-response relationship was documented between the presence of pleural abnormalities and the number of exposure pathways reported by participants. Only 6.7% of the group with "no apparent exposure" had pleural abnormalities, compared to 10.8% of the group reporting one to three exposure pathways, 14.4% of the group reporting four to five exposure pathways, and 23.7% of the group reporting six or more pathways. This trend remained significant even after controlling for body mass index in the multivariate analysis.

We recently evaluated preliminary data from high resolution chest computed tomography (CT) scans conducted on 353 Libby medical screening participants with "indeterminate" chest radiographs. Pleural abnormalities were identified in 98 persons (28% of all tested) whose chest radiographs were classified as "indeterminate" (i.e., only one out of three B-readers noted an abnormality). This suggests that the results of the Libby screening program may have actually underestimated the number of abnormal findings.

In summary, we disagree with Flynn et al.'s assertion that these findings can be explained by study bias issues related to chest radiograph B-readings or by misinterpretation of pleural fat. Rather, more recent high-resolution CT scanning results suggest that our estimates of pleural abnormalities in this population may be conservative and may actually underestimate the true prevalence of these abnormalities seen on chest radiographs.

The authors declare they have no competing financial interests.

Lucy A. Peipins

Centers for Disease Control and Prevention 

Atlanta, Georgia

Michael Lewin

Sharon Campolucci

Jeffrey A. Lybarger

Vikas Kapil

Dan Middleton

Agency for Toxic Substances

and Disease Registry

Atlanta, Georgia

E-mail: [e-mail]

Aubrey Miller

Christopher Weis

U.S. Environmental Protection Agency 

Denver, Colorado

Michael Spence

Montana Department of Health

and Human Services

Helena, Montana

Brad Black

Lincoln County Department of

Environmental Health

Libby, Montana

REFERENCES

Peipins LA, Lewin M, Campolucci S, Lybarger JA, Miller A, Middleton D, et al. 2003. Radiographic abnormalities and exposure to asbestos-contaminated vermiculite in the community of Libby, Montana, USA. Environ Health Perspect 111:1753-1759; doi:10.1289/ehp.6346 [Online 2 July 2003].

Rogan WJ, Ragan NB, Dinse GE. 2000. X-ray evidence of increased asbestos exposure in the US population from NHANES I and NHANES II, 1973-1978. National Health Examination Survey. Cancer Causes Control 11:441-449.

Rogan WJ, Gladen BC, Ragan NB, Anderson HA. 1987. US prevalence of occupational pleural thickening. A look at chest X-rays from the first National Health and Nutrition Examination Survey, Am J Epidemiol 126:893-900.