TABLE. Reported giardiasis outbreaks (N = 111), by mode of transmission and exposure — United States, 2012–2017.
| Transmission mode |
No. (%) |
|
|---|---|---|
| Outbreaks |
Cases |
|
| All modes | 111 (100) | 760 (100) |
|
Waterborne (exposure source)
|
29 (26)
|
370 (49)
|
| Tap water systems* |
9 |
94 |
| Recreational water | ||
| Treated (e.g., pool) |
5 |
19 |
| Untreated (e.g., lake) |
4 |
135 |
| Outdoor freshwater (drinking source) |
7 |
103 |
| Other† |
4 |
19 |
|
Person-to-person (exposure setting)
|
28 (25)
|
129 (17)
|
| Private home/residence |
14 |
47 |
| Child care facilities |
12 |
49 |
| School/College/University |
2 |
33 |
|
Foodborne (food vehicle)
§
|
6 (5)
|
97 (13) |
| Oysters, raw |
3 |
14 |
| Whole milk, unpasteurized |
1 |
38 |
| Mixed green salad |
1 |
25 |
| Undetermined¶ |
1 |
20 |
|
Indeterminate/Unknown (exposure setting)** |
48 (43)
|
164 (22)
|
| Private home/residence |
33 |
93 |
| Child care facilities |
2 |
25 |
| Other†† |
5 |
17 |
| Undetermined§§ | 8 | 29 |
* Includes municipal systems and private wells.
† Other waterborne outbreaks involved the following exposures: undetermined exposure to outdoor freshwater (two), sewage effluent (one), and undetermined exposure to water (one).
§ Includes confirmed and suspected food vehicles.
¶ Foodborne outbreaks were categorized as undetermined if specific food vehicle was not identified or reported.
** Outbreaks were categorized as having an indeterminate/unknown transmission mode if there was insufficient evidence to implicate one specific primary mode of transmission.
†† Indeterminate/unknown outbreaks categorized as “other” involved the following settings: communitywide (one), fair/festival (one), prison/detention center (one), resort (one), workplace (one).
§§ Indeterminate/unknown outbreaks were categorized as undetermined if specific setting was not identified or reported.