Causes of outbreaks associated with drinking water in the United States from 1971 to 2006

Abstract

Since 1971, the CDC, EPA, and Council of State and Territorial Epidemiologists (CSTE) have maintained the collaborative national Waterborne Disease and Outbreak Surveillance System (WBDOSS) to document waterborne disease outbreaks (WBDOs) reported by local, state, and territorial health departments. WBDOs were recently reclassified to better characterize water system deficiencies and risk factors; data were analyzed for trends in outbreak occurrence, etiologies, and deficiencies during 1971 to 2006. A total of 833 WBDOs, 577,991 cases of illness, and 106 deaths were reported during 1971 to 2006. Trends of public health significance include (i) a decrease in the number of reported outbreaks over time and in the annual proportion of outbreaks reported in public water systems, (ii) an increase in the annual proportion of outbreaks reported in individual water systems and in the proportion of outbreaks associated with premise plumbing deficiencies in public water systems, (iii) no change in the annual proportion of outbreaks associated with distribution system deficiencies or the use of untreated and improperly treated groundwater in public water systems, and (iv) the increasing importance of Legionella since its inclusion in WBDOSS in 2001. Data from WBDOSS have helped inform public health and regulatory responses. Additional resources for waterborne disease surveillance and outbreak detection are essential to improve our ability to monitor, detect, and prevent waterborne disease in the United States.

FIG. 1.

Drinking water-associated disease outbreaks (n = 780) reported to WBDOSS by state, 1971-2006, including 15 single cases. Thirteen outbreaks that occurred in Puerto Rico (n = 8), the Virgin Islands (n = 2), the Northern Mariana Islands (n = 1), Palau (n = 1), and the Republic of the Marshall Islands (n = 1) are not shown in the state outbreak counts but are included in the total outbreak count. Two multistate outbreaks (Alabama, Arkansas, Georgia, Kentucky, Louisiana, Missouri, North Carolina, Tennessee, Virginia, and West Virginia; Pennsylvania and Delaware), which are highlighted on the map using blue pentagons and red triangles, respectively, did not contribute to individual state counts. Numbers are dependent on reporting and surveillance activities in individual states and do not necessarily indicate that more outbreaks occurred in a given state.

FIG. 2.

Number of outbreaks associated with drinking water by system type and month (n = 762), 1971 to 2006, excluding outbreaks associated with commercially bottled water (n = 11), bulk water purchase (n = 1), mixed water systems (n = 3), and unknown water systems (n = 3).

FIG. 3.

Percentages of etiologic agents in outbreaks associated with drinking water (n = 780), 1971 to 2006.

FIG. 4.

Number of outbreaks associated with drinking water by water system type and year (n = 780), 1971 to 2006. “Other” includes outbreaks associated with bottled water (n = 11), mixed water system types (n = 3), unknown systems (n = 3), and bulk water purchase (n = 1).

FIG. 5.

Percentages of deficiencies (n = 801) in 780 outbreaks associated with drinking water, 1971 to 2006. The untreated groundwater deficiency category includes one outbreak involving treated groundwater where the treatment provided was not expected to remove the chemical contaminants.

FIG. 6.

Percentages of outbreak deficiencies (n = 671) in public water systems (n = 656) by time period, 1971 to 2006, excluding outbreaks associated with Legionella (n = 24). “Other” includes outbreaks associated with treatment deficiencies in mixed water sources (n = 5) and point of use contamination (n = 7).

FIG. 7.

Percentages of outbreak deficiencies in public water systems associated with untreated and improperly treated source water by year, 1971 to 2006, excluding outbreaks associated with Legionella and treatment deficiencies in mixed water sources. SDWA, Safe Drinking Water Act; SWTR, Surface Water Treatment Rule.

FIG. 8.

Percentages of etiologies in outbreaks associated with public water systems (n = 680) by time period, 1971 to 2006. Not included are two outbreaks involving both a public water system and an individual water system. Outbreaks associated with Legionella were reported only during 2001 to 2006.