Waterborne Disease Outbreaks Associated with Drinking Water: 2009-2010

The Centers for Disease Control and Prevention (CDC) recently released its latest report on waterborne disease outbreaks in drinking water and nonrecreational waters.  This surveillance report covers 2009 and 2010.  CDC collects data on waterborne disease outbreaks submitted from all states and territories through the Waterborne Disease and Outbreak Surveillance System.  During 2009–2010, the most recent years for which finalized data are available, public health officials from 17 states reported 33 drinking water outbreaks.  The outbreaks resulted in 1,040 illnesses, 85 hospitalizations (8.2% of cases), and nine deaths.  At least one causative agent was identified in all but one drinking water outbreak.

Legionella accounted for 58% of outbreaks and 7% of illnesses, and Campylobacter accounted for 12% of outbreaks and 78% of illnesses.  The most commonly identified outbreak deficiencies in drinking water-associated outbreaks were Legionella in plumbing systems (57.6%), untreated ground water (24.2%), and distribution system deficiencies (12.1%).  This means that most of the outbreaks were in areas not usually controlled by public water systems or directly regulated by state drinking water programs.

The majority of outbreaks (75.8%) and outbreak-associated illnesses (79.4%) were linked to community water systems.  The majority of outbreaks (51.5%) and most illnesses (97.3%) occurred in systems that used ground water sources. The majority of outbreaks (57.6%) involved acute respiratory illness, whereas most outbreak-associated illnesses were acute gastrointestinal illness (92.6%).  By deficiency categories, Legionella spp. in plumbing systems was present in the majority of outbreaks (19 [57.6%]); in three Legionella outbreaks, additional deficiencies in building-specific water treatment or plumbing systems were noted.  Untreated ground water deficiency (i.e., contamination of ground water at the source) was identified in eight (24.2%) outbreaks, distribution system deficiency alone was identified in four (12.1%) outbreaks, and both deficiencies were identified in one outbreak (3.0%).  Together, distribution system and untreated ground water deficiencies accounted for 965 (92.8%) of all outbreak-associated illnesses.

All five outbreaks assigned a distribution system deficiency (i.e., distribution system or untreated ground water and distribution system) occurred in systems using ground water or mixed ground and surface water supplies; of these, three occurred in systems supplying unchlorinated ground water.  Two of the distribution system-associated outbreaks (one in an unchlorinated supply) resulted from cross-connections (i.e., direct connections between piped water systems containing potable and nonpotable water).

For more details, including a table of data on each reported outbreak, see the full report.