We derived and refined default alerting filters relevant to the monitor's purview, beginning with three jurisdictional levels: (1) facility; (2) facility group or station, including all clinics and divisions associated with a parent VA medical center; and (3) superuser, referring to routine system-wide monitors. The filters were based on the number of patients, statistical significance of alerts and a composite severity measure. This measure was derived from case-based criteria developed for the Department of Defense ESSENCE (2) and adapted by OPH epidemiologists for the VA population. These criteria are based on separate monitoring of evaluation\management codes for complex cases, OPH-selected procedure codes, 'bounce-backs' to an emergency setting, patient age distributions anomalous for a VA facility and extreme spikes; case disposition was not yet available. We tested candidate filters by tabulating alert rates and sensitivity to known outbreaks using 13 months of all-VA historical outpatient data. For the superuser, the filter required at least one severity factor among records composing an alert, at least 3 cases (5 for the common syndromes) and only p-values B 0.01. These restrictions were reduced in localized user filters.