Legionella Tops the List of Causes of Waterborne Disease Outbreaks

The Centers for Disease Control and Prevention (CDC) recently released their latest surveillance summary of waterborne disease outbreaks in the United States.  This report covers the years 2011 and 2012.  During this period, 32 drinking water–associated outbreaks were reported, accounting for at least 431 cases of illness, 102 hospitalizations, and 14 deaths.  The outbreaks were reported in 14 states.  For an event to be defined as a waterborne disease outbreak, two or more persons must be linked epidemiologically by time, location of water exposure, and case illness characteristics; and the epidemiologic evidence must implicate water as the probable source of illness.

Legionella was implicated in 21 (66%) outbreaks, 111 (26%) cases, 91 (89%) hospitalizations, and all 14 deaths.  Of the Legionella deaths, 12 (86%) were associated with health care facilities.  The two most commonly identified deficiencies leading to drinking water–associated outbreaks were Legionella in building plumbing systems (66%) and untreated groundwater (13%).  Outbreaks associated with community water systems (78.1%) outnumbered those associated with noncommunity systems and bottled water; although the number of cases associated with noncommunity system outbreaks has been increasing in recent years.  Outbreaks associated with water systems that used surface water sources (56.3%) were more frequently reported than outbreaks associated with all other sources.

You may review the complete surveillance report and supporting documentation on CDC’s Morbidity and Mortality Weekly Report (MMWR) web page.