SECTION 9
CONCLUSIONS
The TCE Subregistry population reported more adverse health outcomes when compared with a national sample. The adverse health outcomes reported in excess of those reported by the national sample, for all or specific age groups, included speech impairment, hearing impairment, stroke, liver disease, anemia and other blood disorders, diabetes, kidney disease, urinary tract disorders, and skin rashes.
There also appeared to be an excess number of deaths among TCE registrants when compared with national data but additional information is needed before firm conclusions can be reached. Excess numbers of deaths were found in an older age group of the TCE Subregistry due to cancers of the respiratory system and, when all ages were combined, for heart disease.
Several of the findings were of particular note, including excess numbers of speech and hearing disorders reported in children. Investigations into possible relationships of these outcomes to concurrent or contributing diseases or specific community activities such as hearing testing programs, along with the follow-up data for the TCE Subregistry population, should prove to be useful for clarifying the baseline information.
Of equal concern are the excess reports of stroke and anemia or other blood disorders. These conditions continue to contribute to disease and death in the United States, yet many of the underlying factors that contribute to these outcomes have yet to be identified. In the past, nonoccupational exposures to TCE have not been considered to contribute to either stroke or blood disorders. However, the findings of the subregistry suggest that studies are needed to determine if exposure to TCE might contribute to the development of these conditions. More information from registrants on potentially confounding factors, such as diet, specific health risk behaviors (such as smoking and alcohol consumption), and other lifestyle factors, along with the analyses of the follow-up data for the TCE Subregistry population, will help identify the contributing factors. In addition, future studies of this population should focus on the validation of these findings and exploring if a TCE exposure-health outcome linkage exists.
Many of the conditions reported in excess of the NHIS rates by the TCE Subregistry population, such as diabetes and hypertension, are typically underdiagnosed in the general population. It is possible that the excess reporting of health conditions in the TCE Subregistry population was related to a heightened awareness of the potential for illness that led to either an increased use of health care services or a false increase in reporting.
Limitations of the comparison of the TCE Subregistry data with NHIS data must be kept in mind when interpreting the results. The comparability of the questions (some questions were very closely worded, others were similar), recall bias (exposed persons were perhaps more aware of health problems and remembered events in greater detail), frequency of health care utilization (exposed persons were perhaps more aware of health problems and sought health care more often), and underrepresentation of children younger than 5 years of age in the TCE Subregistry population must be considered when interpreting the results in light of reported national norms. Also, because of the many comparisons carried out, some of the positive results might have been chance occurrences, or might have occurred because the true causal factors (confounders) were not identified.
The limitations of the environmental data for the TCE Subregistry have rendered the dose-response calculations inconclusive. Recently, several computer models (149-151) have become available with which exposure patterns can be simulated with a minimum amount of information. Perhaps these models could be used in conjunction with statistical models to develop a best estimate of actual environmental levels for all exposure periods and sites. If this is feasible, individual doses might be reconstructed for all routes of exposure for further use in dose-response evaluations.
RECOMMENDATIONS
Cause and effect relationships cannot be determined from simple analyses of the subregistry-based information. Information obtained from this database can and will be used to determine appropriate future activities and research. Considerations for further research using this database include modification of the current data collection procedures and methods; exploration of recognized sources of bias and reduction or elimination of these biases; acquisition of additional definitive information on and confirmation of selected outcomes that appear to be in excess; and substance-specific research with specific hypotheses clearly identified.
It is unclear whether either wording differences between TCE Subregistry and NHIS questions or recall bias might have generated different response rates. In order to better understand the excess reporting of some of the health conditions, the Agency for Toxic Substances and Disease Registry (ATSDR) will conduct an evaluation of how these wording differences could have created differences in responses and will modify the questions appropriately for future registry activities. New methods will be considered that could aid in assessing the potential impact of exposure awareness on both the recall of health conditions and health care utilization by registrants. It should be noted that even if a determination is made that exposed people sought health care more often, it will not be possible to separate whether the increase in number of visits was due to an awareness of exposure or from an actual increase in health problems.
Improvement of individual exposure estimates for the TCE Subregistry population and other environmentally exposed populations is a top priority for ATSDR. Better exposure characterization of registrants will allow improved assessment of the relationship between exposure and health outcomes.
Preliminary findings from the completed analyses leave many questions unanswered; it is hoped that additional information and further investigations will help answer these questions. Longitudinal following of the TCE registrants will continue on a routine basis. The additional information collected will be used to assess trends in reporting and to assist in answering or clarifying some of the issues and questions previously discussed.
It should be noted that all of the health conditions that were reported in excess by the TCE subregistry population are preventable or treatable, if not curable. Early detection frequently plays a role in whether a health condition can be arrested or reversed by current medical technologies. Given the results of the baseline analyses for this population, it was imperative that this information be shared with TCE-exposed persons in a responsible manner. A summary version of the TCE Subregistry Baseline Technical Report was composed in nontechnical language for release to the registrants. A Subregistry Technical Assistance Panel (STAP), which was composed of representative membership from the states involved, other federal agencies, and other knowledgeable persons, reviewed the TCE Subregistry Baseline Technical Report and the registrant report and gave ATSDR suggestions and recommendations as to future activities that would be appropriate for follow-up to release of the information.
Following review of the registrant report by the STAP, community representatives, along with interested county, state, and federal agency representatives, met to review the report and to assist ATSDR with planning site-specific activities and with development of a one-page fact sheet summarizing the report. Immediately following these meetings, information packets, containing the registrant report, fact sheet, and cover letter, were mailed to all TCE Subregistry members. Similar information was mailed to the media shortly after the registrants received their information packets.
Public meetings were held in each of the areas with TCE Subregistry sites. The public meetings were conducted to review the purpose of the TCE Subregistry and the information that had been provided to the registrants. Registrants were encouraged to ask questions of ATSDR, either in person or by telephone.
Those registrants expressing specific health concerns were encouraged to see their personal physicians. A concerted effort was made by ATSDR to share the findings of the baseline TCE Subregistry analyses with the appropriate health care providers in each area. In addition, specific information about TCE and training was made available to them.
Although no definitive conclusions can be made from the information contained in this report, it is hoped that researchers will use the information to better assess the potential for adverse health outcomes following exposure to chemicals in the environment. As pointed out, additional studies of the TCE Subregistry data are warranted and encouraged by ATSDR.
Agency for Toxic Substances and Disease Registry, 1825 Century Blvd, Atlanta, GA 30345
Contact CDC: 800-232-4636 / TTY: 888-232-6348
