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Molecular typing returns showing nonpathogenic strains

SW indicates Scottish Water; PAG, policy advisory group; and IMT, incident management team.

SW indicates Scottish Water; PAG, policy advisory group; and IMT, incident management team.

decided to call together its IMT. Within two hours of convening, the IMT decided to issue a boil-water advisory. A boil-water advisory is a general notification to the public to boil tap water before consumption. This decision resulted in considerable activity to disseminate the advisory to the public. The actions included press releases, recorded messages on the water company's call-in lines, loudspeaker trucks, direct contact with large facilities such as hospitals, and postings on Web sites. The notification took approximately three days to complete.

Several weeks later, molecular analysis of the oocysts revealed that they were predominantly species of Cryptosporidia that do not cause disease in humans. In retrospect, the boiling of water was unnecessary.

We cite this example to make two key points about decision making in biosurveillance. First, Glasgow Public Health had considerable difficulty interpreting the available surveillance data (oocyst levels) because the data did not provide a definitive answer to the pivotal question: Were people being exposed to C. parvum or another strain of Cryptosporidium that causes disease in humans? Glasgow Public Health did not know the answer to this question until several weeks later. Second, the IMT did not know the cost or the benefit of a boil-water advisory. The IMT discussed the potential for scalding injuries owing to increased boiling of water over the usual amount of water boiling for the making of tea and coffee, but it had no way to estimate the magnitude of the risk. The IMT did not know the benefit of a boil-water advisory; it did not know its efficacy (the number of cases that might be averted) or the benefit of preventing a case. Corso et al.'s (2003) economic study of the Milwaukee outbreak, estimating a cost of $239 per sick individual in 1993 U.S. dollars, had not yet been published.

Cryptosporidiosis is one of the mildest diseases of concern to a health department. Corso et al.'s estimate of $239 per sick individual reflects the mildness of the disease (although the disease can be disproportionately fatal in immunocompromised patients, as was the case for 85% of the 54 fatalities in the 1993 in Milwaukee outbreak) (Hoxie et al., 1997). Cryptosporidiosis is not a reportable disease in most jurisdictions. However, because this problem could potentially have sickened 400,000 people (as it did in Milwaukee), the mere possibility of it disrupted the city of Glasgow for a week.

Although the boil-water advisory, in retrospect, was unnecessary, the appropriate question to ask is whether the decision was optimal. It remains unknown to this day whether it was optimal and what is—were a heavy rain in Glasgow to lead to a repetition of the above events—the optimal decision. It is similarly unknown what the optimal decision should be if evidence— suggestive, but not conclusive—of a large-scale aerosol release of a biological agent over a city were to present itself tomorrow. There are several accounts of BioWatch signals (DNA-polymerase-based air sampling systems) in Houston and San Diego that raised the specter of a tularemia or other biological agent release. IMTs were convened that considered high stakes decisions under uncertainty and time pressure (Roos, 2003, Houston Department of Health and Human Services, 2003).

Because of the rapid improvement in the world's ability to monitor water, air, and the health of populations, we expect such situations demanding rapid action despite limited information to occur with increasing regularity.

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