Methodological issues in the surveillance of poisoning, illicit drug overdose, and heroin overdose deaths in New Mexico

New Mexico leads the nation in poisoning mortality, which has increased during the 1990s in New Mexico and the United States. Most of this increase has been due to unintentional deaths from illicit drug overdoses. Medical examiner and/or vital statistics data have been used to track poisoning deaths. In this study, the authors linked medical examiner and vital statistics records on underlying cause of death, coded using the International Classification of Diseases, Ninth Revision, to assess the extent to which these data sources agreed with respect to poisoning deaths. The authors used multiple-cause files, which are files with several causes listed for each death, to further assess poisoning deaths involving more than one drug. Using vital statistics or medical examiner records, 94.7% of poisoning deaths were captured by each source alone. For unintentional illicit drug and heroin overdose deaths, each data source alone captured smaller percentages of deaths. Deaths coded as E858.8 (unintentional poisoning due to other drugs) require linkage with medical examiner or multiple-cause records, because this code identifies a significant percentage of illicit drug overdose deaths but obscures the specific drug(s) involved. Surveillance of poisoning death should include the use of medical examiner records and underlying- and multiple-cause vital statistics records.