This study examines healthcare records, for the time period January 1, 2010ÁJune 30, 2011, from a North Carolina-based hospital system composed of three different hospitals for clusters of visits related to exposures. Visits were identified based upon the inclusion of terms in chief complaint data related to chemical, carbon monoxide, meningitis, food poisoning and other types of exposures. For each hospital, time series of visit counts from 1 hour cells, based on patient time-of-visit, were monitored using the past 60 days' cell counts as a baseline. Either a Poisson or a negative binomial distribution was assumed, depending on the baseline mean and variance for each hospital/hour cell. A p-value was calculated for the probability of at least as many visits as observed, and an alert was issued if this value was below 0.01, a threshold chosen to minimize the burden on the PHEs to investigate the alert.