The Decision To Issue A Boilwater Advisory Glasgow 2002

To elucidate the decisions that surround a suspected contamination of a water supply with Cryptosporidia, we consider the events that took place in Glasgow, Scotland, in the summer of 2002. Table 29.1 summarizes the chronology of events as related by the Incident Management Team (IMT) in an "after-action'' report about that event (IMT, 2003).

On July 31, 2002, the day after an unusually heavy rain, Scottish Water (the water department supplying the greater Glasgow area) noted a doubling of turbidity in water from Loch Katrine. Because the community had experienced a

Cryptosporidium outbreak in 2000 from contaminated water, Scottish Water promptly drew samples of water for microscopic analysis.

On August 1, Scottish Water reported oocysts resembling Cryptosporidia to Glasgow Public Health. Cryptosporidia is a genus of parasites that includes several species that may cause gastrointestinal infection in humans. The concentration of oocysts was 0.07 per 10 liters of water (approximately one oocyst per 143 liters of water). Oocyst concentrations in water do not correlate well with levels of disease in human populations. Therefore, Glasgow Public Health decided to await the results from additional samples of water.

On August 2, Scottish Water notified Glasgow Public Health of a higher measurement of oocysts in water. Glasgow Public Health decided to transmit a fax message to physicians heightening suspicion for cryptosporidiosis in patients with gastrointestinal complaints.

On August 3, Scottish Water notified Glasgow Public Health of an even higher reading from a second water source. By this time, Scottish Water had already decided to reconfigure the water system to reduce the population exposed to water from Loch Katrine from 416,000 to 160,000 people. Glasgow Public Health convened its Policy Advisory Group, which promptly

table 29.1 Timeline for Glasgow Cryptosporidium Incident

Date

Time

New Information, Decision, or Action

July 30,2002

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