To develop an onsite syndromic surveillance system for the early detection of public health emergencies and outbreaks at large public events.

As the third largest public health jurisdiction in the United States, Maricopa County Department of Public Health has worked with academic and first-response partners to create an event-targeted syndromic surveillance (EVENTSS) system. This system complements long-standing traditional emergency department-based surveillance and provides public health agencies with rapid reporting of possible clusters of illness.

At 6 high profile events, 164 patient reports were collected. Gastrointestinal and neurological syndromes were most commonly reported, followed by multisyndromic reports. Neurological symptoms were significantly increased during hot weather events. The interview rate was 2 to 7 interviews per 50 000 people per hour, depending on the ambient temperature.

Study data allowed an estimation of baseline values of illness occurring at large public events. As more data are collected, prediction models can be built to determine threshold levels for public health response.

EVENTSS was conducted largely by volunteer public health graduate students, increasing the response capacity for the health department. Onsite epidemiology staff could make informed decisions and take actions quickly in the event of a public health emergency. (Disaster Med Public Health Preparedness. 2013;0:1–8)