TABLE 3.
Etiology of waterborne outbreaks and cases, 1971 to 2006
| Etiologic agent | No. (%) associated with: |
|||||||
|---|---|---|---|---|---|---|---|---|
| Drinking water |
Water not intended for drinking |
Water of unknown intent |
All water types |
|||||
| Outbreaks | Cases | Outbreaks | Cases | Outbreaks | Cases | Outbreaks | Cases | |
| Non-Legionella bacteria | 105 (13.5) | 22,446 (3.9) | 7 (14.9) | 172 (20.0) | 1 (16.7) | 14 (38.9) | 113 (13.6) | 22,632 (3.9) |
| Legionellaa | 24 (3.1) | 126 (0.0) | 9 (19.1) | 241 (28.0) | 5 (83.3) | 22 (61.1) | 38 (4.6) | 389 (0.1) |
| Chemicals | 90b (11.5) | 3,901 (0.7) | 0 | 0 | 0 | 0 | 90 (10.8) | 3,901 (0.7) |
| Parasites | 143 (18.3) | 449,959c (78.0) | 10 (21.3) | 126 (14.6) | 0 | 0 | 153 (18.4) | 450,085 (77.9) |
| Viruses | 64 (8.2) | 16,728 (2.9) | 2 (4.3) | 47 (5.5) | 0 | 0 | 66 (7.9) | 16,775 (2.9) |
| Mixedd | 6 (0.8) | 1,755 (0.3) | 1 (2.1) | 2 (0.2) | 0 | 0 | 7 (0.8) | 1,757 (0.3) |
| Undetermined | 348 (44.6) | 82,179 (14.2) | 18 (38.3) | 273 (31.7) | 0 | 0 | 366 (43.9) | 82,452 (14.3) |
| Total | 780 (100) | 577,094 (100) | 47 (100) | 861 (100) | 6 (100) | 36 (100) | 833 (100) | 577,991 (100) |
a
Outbreaks associated with Legionella were reported only during 2001 to 2006.
b
Includes 15 events in which a single ill person was identified.
c
Includes 403,000 cases from a single cryptosporidiosis outbreak in Milwaukee, WI.
d
More than one infectious agent type (i.e., bacteria, chemicals, parasites, and viruses).