Sentinel health events. A sentinel health event (SHE) is a preventable disease, disability, or untimely death whose occurrence serves as a warning that the quality of preventive or therapeutic medical care might need to be improved (Rutstein et al., 1976). The idea has been refined for application to occupational situations; a SHE(O) is a disease, disability, or untimely death that is related to an occupation and whose occurrence can provide the impetus for epidemiologic or industrial-hygiene studies or serve as a warning signal that material substitution, engineering control, personal protection, or medical care might be required (Rutstein et al., 1983). Wagener and Buffler (1989) showed how NCHS's Compressed Mortality File could be screened with SHE(O) codes to derive mortality rates for as small an area as a county, which would be a step toward identifying geographic areas with increased incidences of sentinel diseases. The industrial or occupational information routinely entered on death certificates is encoded on higher-level, more easily retrievable records in only a few states, however, and that diminishes the usefulness of the SHE(O) idea and of other occupational-surveillance programs that use mortality data. Recently, the SHE(O) principle has been adopted as the core of demonstration reporting projects between NIOSH and 10 state health departments (Baker, 1989). Lead poisoning is one of the eight target occupational-health conditions focused on by this project, the Sentinel Event Notification System for Occupational Risk (SENSOR). This trial surveillance project was described in conjunction with the reporting of a case of adult lead poisoning (blood lead was 170 µg/dl, and reporting is required for concentrations above 25 µg/dl). The index case led to finding secondary cases in the subject's workplace and family (Johnson et al., 1989). The investigators at NIOSH and Harvard Medical School (Rutstein et al., 1983), who developed the original list of SHE(O)s, intended that new associations between toxic environmental exposures and disease conditions be added as they were recognized. The extent to which neurotoxic health effects are indistinct entities will interfere with their conversion into SHEs or SHE(O)s. Neurotoxic conditions that might be added to the list include occupational neuropathy due to Lucel 7 (Horan et al., 1985), paralysis of the urinary bladder after exposure to the NIAX catalyst dimethylaminopropionitrile (Gad et al., 1979; Pestronk et al., 1979), and the Kepone (chlordecone) syndrome (Guzelian, 1982).

Biologic markers. The complexity and inaccessibility of many parts of the nervous system make it difficult to use biologic markers to study neurotoxicology. But events in physiologic systems that are substantially controlled by neuronal processes, such as some aspects of endocrine and immune function, can be monitored. And objective, computer-based systems for assessment of the function of the central and peripheral nervous systems have been developed to yield biologic markers of neurologic function in exposed populations (Letz and Baker, 1986); the tests are rapid, inexpensive, and noninvasive. Some indicators of exposure to neurotoxicants are measurable in easily sampled media, such as blood, urine, and hair. Surveillance for exposure to neurotoxicants is possible with such easily sampled surrogates, as in the measurement of peripheral esterase in workers exposed to organophosphates to monitor CNS effects indirectly (see also Chapter 3).

Disease and exposure registries. Groups of people with known or suspected large exposures to neurotoxicants, such as occupationally exposed populations or residents near hazardous-waste sites, can be included in programs of targeted medical surveillance or followup, e.g., by the Agency for Toxic Substances and Disease Registry (ATSDR).