Syndromic surveillance is a public health tool that analyzes statistical data related to trends in health care as an early warning system. The basis for this type of surveillance is that outbreaks are associated with an increase in medical case loads and other tangible indicators. A number of preclinical factors, including over-the-counter remedy sales, topical Internet searches, and emergency department cases, can often be early warning signs or diagnostic precursors of an outbreak. The New York City DOH and Mental Hygiene currently operate a syndromic surveillance network in New York City (Heffernan et al., 2004). New York City has established a Water-borne Disease Risk Assessment Program to determine Giardia and Cryptosporidium species levels. This program monitors information on cases presumably linked to tap water consumption, so as to ensure rapid detection of any outbreaks. The database maintains information on gastrointestinal disease, particularly emergency department and nursing home statistics, over-the-counter sales for related medicines, and collections of relevant clinical laboratory tests performed. Detailed monitoring of these factors is expected to accelerate the public health response to a biological agent exposure. Additional examples of syndromic surveillance systems are included in two case studies below.
1. An excellent surveillance case study of gastrointestinal illness was performed via retrospective evaluation of pharmacy over-the-counter sales in two Canadian provinces (Edge et al., 2004). The study compared pharmacy sales of antinauseal and antidiarrheal medications, as well as emergency department visits from water-related outbreaks associated with Cryptosporidium, E. coli O157:H7, and Campylobacter species. The investigators compiled these data to assess the potential of a real-time link to outbreaks. Their findings showed that the over-the-counter sales spiked appreciably and correlated well to the outbreak epidemic data. Statistical analysis confirmed that the sales data could be an early indicator to the start of the outbreak periods. This study demonstrated that if public health authorities set up an automated monitoring system covering specific medical supplies, the spatial and temporal trends could be correlated with trends in community health. Such a system would be a huge asset for public health officials and would allow more rapid identification of outbreaks than is possible under the currently available laboratory-based surveillance systems alone.
2. Pascal Beaudeau et al. (1999) studied data from a syn-dromic system that monitored the sale of antidiarrheal medications in Le Havre, France, and they found a correlation between these sales and the failure of a drinking water treatment plant. Specifically, between April 1993 and September 1996, sales of medicine to treat gastrointestinal illness climbed dramatically between 3 and 8 days after interruption of chlorination at the water treatment plant; a sales increase also occurred in the 3 weeks after an increase in raw source water turbidity. There were several instances involving a failure to control turbidity and maintain residual chlorine levels; a significant detail here was that the turbid water still met France's microbiological standards for potable (drinkable) water. The investigators concluded that treatment plant-based monitoring may not be sufficient to consistently prevent contamination of drinking water; the study results also support the value of syndromic surveillance systems that perform signal processing on multiple and disparate data sources.
For the fiscal 2006 year, an approximate $44 million Water Sentinel Initiative has been proposed in which a pilot monitoring and surveillance study of five U.S. urban centers will be developed (Office of Management and Budget, 2005). The program will attempt to incorporate standardized syndromic surveillance systems, such as RODS and the Department of Defense's Electronic Surveillance System for the Early Notification of Community-based Epidemics (ESSENCE), in its mandate to provide an early warning system for chemical and biological contamination. This initiative is expected to ultimately result in a national surveillance system capable of greatly heightened monitoring of our water supply.
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