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Institute of Medicine (US) Committee to Review the Federal Response to the Health Effects Associated with the Gulf of Mexico Oil Spill; Goldman L, Mitchell A, Patlak M, editors. Review of the Proposal for the Gulf Long-Term Follow-Up Study: Highlights from the September 2010 Workshop. Washington (DC): National Academies Press (US); 2010.

Cover of Review of the Proposal for the Gulf Long-Term Follow-Up Study

Review of the Proposal for the Gulf Long-Term Follow-Up Study: Highlights from the September 2010 Workshop.

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Exposure Assessment Challenges

The workshop participants had much discussion about the difficulties in obtaining accurate and comprehensive exposure information on participants in the GuLF study, because many of those assessments will be made several months after the workers were exposed, hampering accurate recall and sampling efforts. As several participants pointed out, the immediate concerns of the public health officials who responded to the oil spill were protecting the workers and community members from contamination and not collecting the samples and information needed to ascertain exposure for a future research study, such as the GuLF study. In addition, many workers will have had multiple exposures during the oil spill, and the intensity of those exposures will vary over time, such that single exposure measurements may not be sufficient to fully assess total exposure.

“Exposure is oftentimes the Achilles heel of large-scale population studies, especially retrospective ones or ones that are being done in an emergent way,” said David Kalman. “There are a lot of reasons to be concerned about exposure misclassification,” he stressed.

Consequently, researchers should validate exposure assessments and pay attention to what approaches they use to deal with missing data, several participants suggested. Stephen Cole from the University of North Carolina, Chapel Hill, strongly stressed the importance of doing formal sensitivity analyses to test the validity of the exposure assumptions made in the study, especially since the study will not be randomized. Others suggested the usefulness of a data-monitoring committee.

Dr. Kalman suggested validating exposures by using multiple, overlapping exposure information on the study participants, including information from employers, the participants themselves, and the various groups doing exposure monitoring in the area, such as BP and the U.S. Coast Guard. “There is a ton of stuff. If it can in fact be brought to bear on this study in an ideal way, it will help a lot with the lack of real time measurement,” Dr. Kalman said. He pointed out that because cleanup activities are ongoing, researchers can collect additional data that can be used to validate approaches to exposure evaluation. “This is a door of opportunity that is closing. So, if it were a tradeoff between getting it perfectly six months from now or getting it mostly right six weeks from now, I would vote for the later,” Dr. Kalman said. Dr. Cole noted that multiple measures of exposure may be needed to adequately analyze the data, and Roberta Ness suggested that all relevant information that can be used to analyze exposure be collected, including food and water samples. Bernard Goldstein added that biological markers of exposure could be helpful after oil spills but that most do not persist long enough to be of value to the GuLF study at this late date.

David Cohen, a member of the IOM committee, suggested that key to assessing exposure accurately will be determinations of whether workers used the personal protective equipment that was given to them and whether they had additional personal hygiene habits that might have further limited their exposure.

Dr. Cole suggested considering in advance the types of data analyses that will need to be done and the likely confounders, as these will determine the study design and what data are collected. He also suggested doing partial random sampling to have a more powerful study.

Lawrence Engel, a coinvestigator of the GuLF study, responded that exposure assessments done in the GuLF study will include determining what cleanup tasks were done, whether there was dermal or other types of contact, and whether personal protective equipment was used while the study participants were doing those tasks. He added that plans have been made to do a sensitivity analysis of the exposure assumptions. Dr. Engel also recognized the potential problem with exposure misclassification but noted that there are legal limitations to the data that they can collect from employers that may improve exposure classifications. He added that the investigators plan to validate the exposure data for a small subset of participants.

Dr. Engel said that the concerns about using an appropriate control group were valid and that the workers with the greatest exposure will be compared to the workers with the lowest exposure to help address bias issues to some degree. Limited data from NIOSH and other sources can also be used to assess how workers who opt to participate in the study differ from those who decline participation.

Lynn Goldman, chair of the IOM committee, noted that the longer that it takes to conduct exposure assessments, the less accurate those assessments will be and suggested starting the passive phase of the study as quickly as possible while figuring out the protocols for the active and biomedical components of the study. Doing the study in stages would make sure that the investigators gathering the passive information would still have that crucial window of opportunity that closes shortly after the exposure occurs.

Copyright © 2010, National Academy of Sciences.
Bookshelf ID: NBK50907

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