An investigation of a workplace cluster of Bell's palsy.

We undertook a study to confirm the existence of an apparent cluster of Bell's palsy in an industrial plant ("W4"), and to test etiologic hypotheses regarding chemical exposures, immune suppression, and infectious etiologies. Cases were enumerated by questionnaire. Employees with a history of Bell's palsy ("cases") were invited to participate in a study that included medical history, T cell studies, viral and Lyme disease serologies, and blink reflex studies. Thirty-three unaffected volunteers from W4 and 32 from a comparison building were also tested. Extensive environmental studies were carried out in W4, evaluating infectious, chemical, and radiation exposures. The lifetime incidence of self-reported Bell's palsy was 11.6/10,000 person-years (P-Y) in W4 and 2.4 cases/10,000 P-Y in the comparison building (RR = 4.8, P < .05); the comparison rate was similar to that reported in previous population studies. When restricted to cases occurring after the onset of work, the W4 incidence was 29.2 cases/10,000 P-Y, compared to 4.8 cases/10,000 P-Y in the comparison building (RR = 6.1, P < .05). The cases and noncases did not differ with respect to clinical histories or infectious disease titers. The W4 noncases had small but significant decreases in T lymphocyte (1974 +/- 86 vs 2291 +/- 103) and CD4 (1083 +/- 318 vs 1459 +/- 494) counts compared to the remote noncases. The cases had significantly prolonged RR1, LR1, and LFC values compared to both groups of noncases. No medical or environmental factors were identified that could explain an excess of disease.