A neurological disease cluster at a manufacturing plant

A case-control study was conducted an at automotive carburetor plant to investigate exposures associated with a cluster of cases exhibiting neurological symptoms that resembled multiple sclerosis. Eighteen cases were identified with symptom onset between 1970 and 1985. Four controls per case were selected randomly from the plant population, and they were matched by year of birth, gender, and ethnicity. From work histories and telephone interviews, cumulative exposures for 10 chemical or process categories were computed, based on rank estimates of exposure levels. Mantel-Haenszel procedures and logistic regression modeling produced statistically significant relative risks associated with die-casting and organophosphate exposures, using unweighted and latency-weighted cumulative exposures. The study was hampered by the inability to pursue further clinical neurological evaluation of the cases, by the small number of cases, and by uncertainties of exposure assessment. A delayed neuropathy arising from organophosphate exposure in hydraulic and machining fluids is proposed.