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Surveillance for Waterborne Disease Outbreaks Associated with Drinking Water

The Centers for Disease Control and Prevention (CDC) has just released the latest report of waterborne disease outbreaks associated with drinking water covering 2007 and 2008.  More than half the outbreaks were associated with untreated or inadequately treated ground water.  Two thirds of the outbreaks associated with untreated ground water were in public water supplies.

Since 1971, CDC, the EPA and the Council of State and Territorial Epidemiologists have collaborated on the Waterborne Disease and Outbreak Surveillance System (WBDOSS) for collecting and reporting data related to occurrences and causes of waterborne disease outbreaks associated with drinking water.  This surveillance system is the primary source of data concerning the scope and health effects of waterborne disease outbreaks in the U.S.   The data presented in the report summarize 48 outbreaks that occurred during January 2007 to December 2008 and 70 previously unreported outbreaks.  The 70 previously unreported outbreaks included 69 Legionella outbreaks during the period 1973 -2000 that were not reportable previously.   WBDOSS includes data on outbreaks associated with drinking water, recreational water, water not intended for drinking (WNID) (excluding recreational water), and water use of unknown intent (WUI).  Only data on outbreaks associated with drinking water, WNID (excluding recreational water), and WUI are summarized in this report. Outbreaks associated with recreational water are reported separately.

A total of 24 states and Puerto Rico reported the 48 outbreaks.  Of these 48 outbreaks, 36 were associated with drinking water, eight with WNID, and four with WUI. The 36 drinking water associated outbreaks caused illness among at least 4,128 persons and were linked to three deaths.  Of the 36 drinking water associated outbreaks, 22 were outbreaks of acute gastrointestinal illness (AGI), 12 were outbreaks of acute respiratory illness (ARI) (all from Legionella), one was an outbreak associated with skin irritation, and one was an outbreak of hepatitis.  A total of 37 deficiencies were identified in the 36 outbreaks associated with drinking water.  Of the 37 deficiencies, 59.5% involved contamination at or in the source water, treatment facility, or distribution system; 35.1% occurred at points not under the jurisdiction of a water utility; and 5.4% had unknown/insufficient deficiency information. Among the 21 outbreaks associated with source water, treatment, or distribution system deficiencies, 16 occurred in public water systems, and five outbreaks occurred in individual systems (all of which were associated with untreated ground water).

The data provided in this report highlight two primary findings.  The first is the high proportion of outbreaks associated with contaminated ground water, whether consumed untreated or with inadequate treatment.  This is consistent with data from 1971-2006 indicating that ground water outbreaks comprised the majority of drinking water outbreaks and showed no decrease over time.  The second finding is that Legionella was again the most frequently reported etiology among drinking water associated outbreaks, following the pattern observed since it was first included in WBDOSS in 2001.

The full report may be reviewed and downloaded at http://www.cdc.gov/mmwr/mmwr_ss/ss_cvol.html.  The report for recreational water is also available at this site.