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Syndromic surveillance.

Michael A. Stoto's "Syndromic Surveillance" (Issues, Spring 2005) catalogues numerous reasons why these early warning systems for large outbreaks of disease will disappoint the thousands of U.S. counties and cities planning to implement them. Besides suffering from high rates of expensive false positive and useless false negative results, syndromic surveillance algorithms only work when very large numbers of victims show up within a short period of time. When they produce a true positive, they don't tell you what you're dealing with, so they must be coupled with old-fashioned epidemiology, which trims the earliness of the early warning. Most disturbingly, when challenged by historical or simulated data, they tend to fail as often as they pass. It seems that, like missile defense but on a vastly smaller scale, syndromic surveillance has become yet another public expenditure on something that is not expected to work in the name of defending the homeland. The up side is that epidemiologists will have to be hired to investigate the syndromic surveillance alarms. They might find something interesting while investigating false positives and, if there were a bioterrorist attack, the extra workers would come in handy.


Associate Research Professor

Department of Engineering and Public Policy

Carnegie Mellon University

Pittsburgh, Pennsylvania

Syndromic surveillance systems monitor pre-diagnostic data (such as work absenteeism or ambulance dispatch records) to identify, as early as possible, trends that may signal disease outbreaks caused by bioterrorist attacks. Michael A. Stoto summarizes some of the main questions being asked about syndromic surveillance and the lines of research currently being pursued in order to supply the answers.

Syndromic surveillance is a relatively young field. It was given a push by the events of 9/11, which generated a huge amount of investment in developing systems designed to detect the effects of bioterrorist attacks. The acute necessity for counterterrorism measures meant that the proof of concept often required of new technologies before public investment is made was initially ignored. This has resulted in the proliferation of surveillance systems, all with similar aims and all now understandably looking to justify several years of investment.

In the absence of any known bioterrorist attacks since 2001, it is instructive to examine the benefits of syndromic surveillance (some mentioned in Stoto's article), which go beyond bioterrorism preparedness. They include the early detection of naturally occurring infectious disease outbreaks (the majority being viral in nature); the provision of timely epidemiological data during outbreaks; the strengthening of public health networks as a result of the follow-up of syndromic surveillance signals; the identification of secular disease trends; the flexibility to be "tweaked" in response to new threats (such as forest fires, heat waves, or poisonings from new market products); and reassurance that no attack has taken place during periods of increased risk.

There is some discussion in Stoto's article about the distinction between the generation of surveillance signals and the use of those signals thereafter. This distinction is crucial to the ultimate success of syndromic surveillance systems. A simple and widely accepted definition of disease surveillance is that it is "information for action." In other words, although syndromic surveillance systems excel at generating signals from noisy data sets, the challenge is how to filter out the false positives and turn the remaining true positives into effective public health action (a reduction in morbidity and mortality). To facilitate public health action, surveillance teams must wrestle with a complex array of jurisdictional, legal, and ethical issues as well as epidemiological ones. A multitude of skills are needed to do this.

Those public health practitioners used to traditional laboratory surveillance may be resistant to, or simply not understand, the new technology. Education and careful preparation must be used to ensure that syndromic surveillance employees communicate effectively with colleagues in other areas, that timely but nonspecific syndromic signals are validated with more definitive laboratory analyses, and that those on the receiving end of surveillance signals know how to respond to them. It is essential that investigations of signals that turn out to be spurious, as well as those representing real outbreaks, be published so that a portfolio of best practice can be developed. Finally, there must be a recognition that the benefits of syndromic surveillance fall not only in infectious disease monitoring and biosurveillance but also in other areas, some potentially not yet realized. The discussion of this topic within this journal's broad scientific remit is therefore welcomed.


Senior Scientist

Health Protection Agency West Midlands

Birmingham, England

Michael A. Stoto confidently straddles the ambivalent line between those who extol the virtues of syndromic surveillance and those who question the resources dedicated to its development. As a public health practitioner, it is refreshing to have the concerns articulated so clearly, yet without minimizing a new public health tool that potentially offers actionable medical information.

The author makes several points that are beyond dispute, including that many city, county, and state health agencies have begun spending substantial sums of money to develop and implement syndromic surveillance systems, and that too many false alerts generated from a system will desensitize responders to real events. Our impatience to build systems is rooted in the desire to improve our nation's capacity to rapidly detect and respond to infectious disease scourges. Although it is difficult to argue this logic, Stoto appropriately clarifies cavalier statements, such as that syndromic surveillance is cost-effective because it relies on existing data. There is a high cost to these systems, too often without any evaluation of real benefits as compared to those of existing disease detection systems. Protection of patient privacy is another concern. Patient support for these systems could falter if their identities are not protected.

Public health departments need surveillance systems that are strategically integrated with existing public health infrastructure (many systems are outside public health, in academic institutions), and, more importantly, that are accompanied by capacity-building--meaning sufficient, permanent, and well-trained staff that can perform a range of functions. Ignoring these issues may prove to be self-destructive, as fractionated systems multiply and limited public health resources are spent to respond repeatedly to phantom alerts (or health directors begin to downplay alerts).

The offering of a possible supplementary "active syndromic surveillance" approach is appealing and strengthens the agreed-on benefits of syndromic surveillance: new opportunities for collaboration and data sharing between health department staff and hospital staff along with their academic partners, as well as reinforcement of standards-based vocabulary to achieve electronic connectivity in health care.

A stronger message could be sent. Although they are intuitively appealing and growing each year, syndromic surveillance systems do not relieve ambitious developers or funders from executing systems that are better integrated (locally and regionally) and evaluated and have the skilled staff needed to detect and respond to alerts. We must strike a better balance between strengthening what is known to be helpful (existing infectious disease surveillance systems, improved disease and laboratory reporting, and distribution of lab diagnostic agents) and the exploration of new technology.


Senior Epidemiologist

San Diego County, Health and Human Services

Associate Research Professor, Epidemiology

Graduate School of Public Health

San Diego State University

We wholeheartedly support Michael A. Stoto's thesis that syndromic surveillance systems should be carefully evaluated and that only through continued testing and evaluation can system performance be improved and surveillance utility assessed. It is also undeniable that there is a tradeoff between sensitivity and specificity and that it is highly unlikely that syndromic surveillance systems will detect the first or even fifth case of a newly emerging outbreak. However, syndromic surveillance does allow for population-wide health monitoring in a time frame that is not currently available in any other public health surveillance system.

The track record of reliance on physician-initiated disease reporting in public health has been mixed at best. Certainly, physician reporting of sentinel events, such as occurred with the index cases of West Nile virus in New York City in 2000 and with the first case of mail-associated anthrax in 2001, remain the backbone of acute disease outbreak detection. However, the completeness of medical provider reporting of notifiable infectious diseases to public health authorities between 1970 and 1999 varied between 9 and 99 percent, and for diseases other than AIDS, sexually transmitted diseases, and tuberculosis, it was only 49 percent. The great advantage of using routinely collected electronic data for public health surveillance is that it places no additional burden on busy clinicians. The challenge for syndromic surveillance is how to get closer to the bedside, to obtain data of greater clinical specificity, and to enable two-way communication with providers who can help investigate signals and alarms.

The solution to this problem is not a return to "active syndromic surveillance," which would require emergency department physicians to interrupt their patient care duties to enter data manually into a standalone system. Such a process would be subject to all the difficulties and burdens of traditional reporting without its strengths, and is probably not where the field is headed.

The development of regional health information organizations and the increasing feasibility of secure, standards-based, electronic health information exchange offer the possibility of real-time syndromic surveillance and response through linkages to electronic health records. The future of public health surveillance may lie in a closer relationship with clinical information systems, rather than a step away from them.


Special Advisor

Office of the Commissioner


Assistant Commissioner

Division of Epidemiology

New York City Department of Health and Mental Hygiene

New York, New York

Michael A. Stoto's article performs a useful service by subjecting a trendy new technology to evidence-based analysis and discovering that it comes up short. All too often, government agencies adopt new technologies without careful testing to determine whether they actually work as advertised and do not create new problems. Tellingly, Stoto writes that one reason why state and local public health departments find syndromic surveillance systems attractive is that "personnel ceilings and freezes in some states ... have made it difficult for health departments to hire new staff." Yet he points out later in the article that syndromic surveillance merely alerts public health officials to possible outbreaks of disease and that "its success depends on local health departments' ability to respond effectively." Ironically, because epidemiological investigations are labor-intensive and syndromic surveillance can trigger false alarms, the technology may actually exacerbate the personnel shortages that motivated the purchase of the system in the first place.


Senior Research Fellow

Center for Nonproliferation Studies

Monterey Institute of International Studies

Washington, D.C.
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Title Annotation:FORUM; epidemiology
Author:Casman, Elizabeth; Cooper, Duncan; Gresham, Louise S.; Henning, Kelly J.; Mostashari, Farzad; Tucker
Publication:Issues in Science and Technology
Date:Jun 22, 2005
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