involved in characterizing and reconstructing the herbicide exposures of Vietnam veterans.
The original VAO committee and the update committees up to that for Update 2006 have been satisfied with exposure characterization as nonspecific as “usual occupation” on a death certificate or “current occupation” from a census. With the passage of time, exposure assessments in epidemiology studies have been increasingly exact in both specificity and amount, and this has led the members of the more recent updates to establish stricter criteria for accepting exposure as sufficiently specific for results to be added to the evidentiary database. The current committee now seeks results expressed in terms of the five chemicals of interest for this project or their analogues and regards classification based only on job title as inadequate; restriction by the investigators to “herbicide” exposure is considered specific enough only to provide supporting evidence. According to the policy established by the Agent Orange Act of 1991, studies of Vietnam veterans are presumed to involve relevant exposure, as are studies of workers at a particular plant during a period when it is known to have been producing phenoxy herbicides or other chemicals recognized as having been contaminated with TCDD.
In Update 2010, the committee undertook a major change in the formatting of the tables of cumulative results on the health outcomes that was aimed at making relationships among publications more evident for its own deliberations and for the reader. The prior practice had been to insert findings from new publications in the results tables at the beginning of the sections on veteran, occupational, and environmental studies and so to create bands of studies reviewed in individual updates. Now, however, the reported findings on a given condition from a particular study population described in any of the VAO reports are gathered and presented in reverse chronologic order to provide the full history of the study of each endpoint in each group studied. The current update has attempted to shift the focus further to the total picture presented by a study population by clustering related findings and shifting the citations that were the source of particular results to the far right of the results tables. For instance, all incidence findings on the Seveso cohort over the successive followup periods are grouped first, and they are followed by all the analogous mortality findings, even when that means separating various sorts of results from the same publication.
Within the three general types of exposure that cohorts or cross-sectional study populations may have experienced, the order of the study populations (Vietnam veterans, occupationally exposed workers, and environmentally exposed people) roughly reflects the degree of importance attributed to the information generated. In the present update, the occupational-study populations have been partitioned into those involved in the production of herbicides and other industrial products contaminated with TCDD and those involved in occupational use of the herbicides of interest, because of substantial differences in the nature and intensity of their exposures. Doing so entailed splitting the findings on sprayers