Surveillance for waterborne disease outbreaks associated with drinking water---United States, 2007--2008

MMWR Surveill Summ. 2011 Sep 23;60(12):38-68.


Problem/condition: Since 1971, CDC, the Environmental Protection Agency (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 United States.

Reporting period: Data presented summarize 48 outbreaks that occurred during January 2007--December 2008 and 70 previously unreported outbreaks.

Description of system: 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). Public health agencies in the states, U.S. territories, localities, and Freely Associated States are primarily responsible for detecting and investigating outbreaks and reporting them voluntarily to CDC by a standard form. 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.

Results: A total of 24 states and Puerto Rico reported 48 outbreaks that occurred during 2007--2008. 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. Etiologic agents were identified in 32 (88.9%) of the 36 drinking water--associated outbreaks; 21 (58.3%) outbreaks were associated with bacteria, five (13.9%) with viruses, three (8.3%) with parasites, one (2.8%) with a chemical, one (2.8%) with both bacteria and viruses, and one (2.8%) with both bacteria and parasites. Four outbreaks (11.1%) had unidentified etiologies. Of the 36 drinking water--associated outbreaks, 22 (61.1%) were outbreaks of acute gastrointestinal illness (AGI), 12 (33.3%) were outbreaks of acute respiratory illness (ARI), one (2.8%) was an outbreak associated with skin irritation, and one (2.8%) was an outbreak of hepatitis. All outbreaks of ARI were caused by Legionella spp. A total of 37 deficiencies were identified in the 36 outbreaks associated with drinking water. Of the 37 deficiencies, 22 (59.5%) involved contamination at or in the source water, treatment facility, or distribution system; 13 (35.1%) occurred at points not under the jurisdiction of a water utility; and two (5.4%) had unknown/insufficient deficiency information. Among the 21 outbreaks associated with source water, treatment, or distribution system deficiencies, 13 (61.9%) were associated with untreated ground water, six (28.6%) with treatment deficiencies, one (4.8%) with a distribution system deficiency, and one (4.8%) with both a treatment and a distribution system deficiency. No outbreaks were associated with untreated surface water. Of the 21 outbreaks, 16 (76.2%) occurred in public water systems (drinking water systems under the jurisdiction of EPA regulations and water utility management), and five (23.8%) outbreaks occurred in individual systems (all of which were associated with untreated ground water). Among the 13 outbreaks with deficiencies not under the jurisdiction of a water system, 12 (92.3%) were associated with the growth of Legionella spp. in the drinking water system, and one (7.7%) was associated with a plumbing deficiency. In the two outbreaks with unknown deficiencies, one was associated with a public water supply, and the other was associated with commercially bottled water. The 70 previously unreported outbreaks included 69 Legionella outbreaks during 1973--2000 that were not reportable previously to WBDOSS and one previously unreported outbreak from 2002.

Interpretation: More than half of the drinking water--associated outbreaks reported during the 2007--2008 surveillance period were associated with untreated or inadequately treated ground water, indicating that contamination of ground water remains a public health problem. The majority of these outbreaks occurred in public water systems that are subject to EPA's new Ground Water Rule (GWR), which requires the majority of community water systems to complete initial sanitary surveys by 2012. The GWR focuses on identification of deficiencies, protection of wells and springs from contamination, and providing disinfection when necessary to protect against bacterial and viral agents. In addition, several drinking water--associated outbreaks that were related to contaminated ground water appeared to occur in systems that were potentially under the influence of surface water. Future efforts to collect data systematically on contributing factors associated with drinking water outbreaks and deficiencies, including identification of ground water under the direct influence of surface water and the criteria used for their classification, would be useful to better assess risks associated with ground water. During 2007--2008, Legionella was the most frequently reported etiology among drinking water--associated outbreaks, following the pattern observed since it was first included in WBDOSS in 2001. However, six (50%) of the 12 drinking water--associated Legionella outbreaks were reported from one state, highlighting the substantial variance in outbreak detection and reporting across states and territories. The addition of published and CDC-investigated legionellosis outbreaks to the WBDOSS database clarifies that Legionella is not a new public health issue. During 2009, Legionella was added to EPA's Contaminant Candidate List for the first time.

Public health actions: CDC and EPA use WBDOSS surveillance data to identify the types of etiologic agents, deficiencies, water systems, and sources associated with waterborne disease outbreaks and to evaluate the adequacy of current technologies and practices for providing safe drinking water. Surveillance data also are used to establish research priorities, which can lead to improved water quality regulation development. Approximately two thirds of the outbreaks associated with untreated ground water reported during the 2007--2008 surveillance period occurred in public water systems. When fully implemented, the GWR that was promulgated in 2006 is expected to result in decreases in ground water outbreaks, similar to the decreases observed in surface water outbreaks after enactment of the Surface Water Treatment Rule in 1974 and its subsequent amendments. One third of drinking water--associated outbreaks occurred in building premise plumbing systems outside the jurisdiction of water utility management and EPA regulations; Legionella spp. accounted for >90% of these outbreaks, indicating that greater attention is needed to reduce the risk for legionellosis in building plumbing systems. Finally, a large communitywide drinking water outbreak occurred in 2008 in a public water system associated with a distribution system deficiency, underscoring the importance of maintaining and upgrading drinking water distribution system infrastructure to provide safe water and protect public health.

MeSH terms

  • Acute Disease
  • Disease Outbreaks*
  • Environmental Exposure
  • Gastrointestinal Diseases / epidemiology*
  • Gastrointestinal Diseases / microbiology
  • Gastrointestinal Diseases / parasitology
  • Gastrointestinal Diseases / virology
  • Humans
  • Legionella / isolation & purification
  • Legionellosis / epidemiology*
  • Population Surveillance*
  • Respiratory Tract Diseases / epidemiology
  • Respiratory Tract Diseases / microbiology
  • Respiratory Tract Diseases / parasitology
  • Respiratory Tract Diseases / virology
  • Skin Diseases / epidemiology
  • Skin Diseases / microbiology
  • Skin Diseases / parasitology
  • United States / epidemiology
  • Water Microbiology*
  • Water Pollutants
  • Water Purification
  • Water Supply* / standards


  • Water Pollutants