N.Y. computer detects outbreaks of disease

Syndromic Surveillance called the most advanced health warning system

April 13, 2003|By Richard Perez-Pena | Richard Perez-Pena,NEW YORK TIMES NEWS SERVICE

NEW YORK -- A corner of Queens recently suffered a sudden, sharp increase in the number of people with fever and trouble breathing, turning up mostly at one hospital's emergency room. Where a statistical analysis said there should have been seven such cases over three days, there were 23. The next day, there were 47.

Suspecting an outbreak of severe acute respiratory syndrome, or SARS, a team of city health workers fanned out, questioning doctors, nurses and patients about symptoms, travels and recoveries, and making plans to isolate them if necessary. It turned out to be a false alarm, a statistical anomaly brought on by conditions as disparate as kidney stones and asthma.

What was remarkable about that episode was not so much the city's response, but that it was detected at all. No one at the hospital noticed it. (City officials would not identify the hospital or the neighborhood.)

Rather, the increase was caught by a computer at the New York City Department of Health and Mental Hygiene's headquarters in Lower Manhattan, where a statistical analysis program warned that there was only a 1 in 1,000 chance of such a thing being a random occurrence.

Syndromic Surveillance

This was the work of the city's Syndromic Surveillance System, which public health experts call the most advanced early-warning system for possible disease outbreaks in the country. Amid growing national concern about bioterrorism and the spread of exotic diseases, a number of cities have become interested in this field, and many have called New York, hoping to learn how it is done.

"New York City is clearly at the cutting edge of this, the model for others to follow," said Paula J. Olsiewski, a program director of the Alfred P. Sloan Foundation, a philanthropic group that has financed the development of syndromic surveillance software.

The nearest analogy may be to Compstat, the Police Department's vaunted crime-fighting computer system, used since the early 1990s to sort mounds of data every day so that the police can respond to problems as soon as they crop up.

The Health Department built its system in fits and starts over several years, but the effort did not really take off until after the World Trade Center and anthrax attacks in 2001. Now, the system, which costs about $1 million a year in labor and computer expenses, analyzes more than 50,000 pieces of information daily, including 911 calls, emergency room visits and drugstore purchases, sifting them for patterns that might escape human notice.

"Our system routinely picks up patterns that were never caught before," said Dr. Don Weiss, medical director of the department's communicable disease surveillance unit.

Several other cities have similar efforts under way, including Boston, Los Angeles and Washington, but none is as well developed as New York City's, experts say. New York state officials are considering building a statewide system, modeled on the city's.

Now, New York City officials who spent years proselytizing about the virtues of syndromic surveillance find themselves warning against inflated expectations.

"This system is probably going to be far more useful in detecting natural outbreaks than man-made ones," said Dr. Farzad Mostashari, assistant commissioner for epidemiology services for the Health Department. "There is no guarantee that it will detect even a modest-sized bioterror attack, or that it will detect that attack before an astute clinician would. This is still in its infancy. It's very much a work in progress."

The anthrax attacks and the West Nile virus illustrate perfectly the limitations, city officials say. Each episode began with a mere handful of cases, most of them nonfatal, involving mostly run-of-the-mill symptoms like fevers. Neither case would have offered enough evidence to register against the background noise of a city of 8 million people and their ailments -- at least, not until long after some sharp-eyed doctors had figured out what was happening.

Still, the system is a significant departure from traditional epidemiology, which tracks and responds to patterns of disease. Syndromic surveillance focuses not on diseases, but on syndromes -- symptoms -- that might offer signs of a disease a day or even a week before the disease itself becomes apparent.

Once a week

About once a week, New York City's system turns up something that officials decide warrants a second look. Most turn out to be nothing, but not all. The system spots the onset of flu season earlier than the traditional reliance on anecdotal reports from doctors, and it detected a surge in sales of nicotine patches immediately after a big increase in cigarette taxes took effect last year.

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