A recent report shows that for 2011–2012, 32 drinking water–associated outbreaks were reported, accounting for at least 431 cases of illness, 102 hospitalizations, and 14 deaths.
Legionella was responsible for 66% of outbreaks and 26% of illnesses, and viruses and non-
Legionella bacteria together accounted for 16% of outbreaks and 53% of illnesses. The two most commonly identified deficiencies leading to drinking water–associated outbreaks were
Legionella in building plumbing systems (66%) and untreated groundwater (13%). The
report has an in-depth analysis of the outbreak data but cautions that the detection and investigation of outbreaks might be incomplete, because linking illness to drinking water is inherently difficult and the level of surveillance and reporting activity, as well as reporting requirements, vary across states and localities.