TABLE.
Number of waterborne disease outbreaks associated with recreational water (n = 81), by etiology and type of water exposure — United States, 2009–2010
| Etiology | Type of water exposure | Total | |||||||
|---|---|---|---|---|---|---|---|---|---|
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| Treated | Untreated | ||||||||
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| Outbreaks | Cases* | Hospitalized | Outbreaks | Cases* | Hospitalized | Outbreaks (%)† | Cases* (%) | Hospitalized (%) | |
| Bacterium | 10 | 75 | 11 | 5 | 91 | 18 | 15 (19) | 166 (13) | 29 (47) |
| Campylobacter jejuni | 0 | 0 | 0 | 1 | 6 | 4 | 1 | 6 | 4 |
| Escherichia coli O157:H7 | 1 | 14 | 4 | 3 | 17 | 8 | 4 | 31 | 12 |
| Legionella spp. | 4 | 8 | 7 | 0 | 0 | 0 | 4 | 8 | 7 |
| Pseudomonas aeruginosa | 4 | 50 | 0 | 0 | 0 | 0 | 4 | 50 | 0 |
| Shigella sonnei | 1 | 3 | 0 | 1 | 68 | 6 | 2 | 71 | 6 |
| Parasite | 25 | 413 | 15 | 3 | 16 | 0 | 28 (35) | 429 (32) | 15 (24) |
| Cryptosporidium spp. | 24 | 406 | 14 | 3 | 16 | 0 | 27 | 422 | 14 |
| Giardia intestinalis | 1 | 7 | 1 | 0 | 0 | 0 | 1 | 7 | 1 |
| Virus | 0 | 0 | 0 | 1 | 69 | 2 | 1 (1) | 69 (5) | 2 (3) |
| Norovirus | 0 | 0 | 0 | 1 | 69 | 2 | 1 | 69 | 2 |
| Chemical | 0 | 0 | 0 | 4 | 38 | 1 | 4 (5) | 38 (3) | 1 (2) |
| Cyanobacterial toxin(s)§ | 0 | 0 | 0 | 4 | 38 | 1 | 4 | 38 | 1 |
| Multiple ¶ | 0 | 0 | 0 | 1 | 45 | 0 | 1 (1) | 45 (3) | 0 (0) |
| Campylobacter jejuni, norovirus genogroup I, Shigella sp. | 0 | 0 | 0 | 1 | 45 | 0 | 1 | 45 | 0 |
| Unidentified | 22 | 542 | 14 | 10 | 37 | 1 | 32 (40) | 579 (44) | 15 (24) |
| Suspected avian schistosomes | 0 | 0 | 0 | 2 | 11 | 0 | 2 | 11 | 0 |
| Suspected chemical exposure** | 8 | 54 | 1 | 0 | 0 | 0 | 8 | 54 | 1 |
| Suspected chloramines** | 2 | 311 | 0 | 0 | 0 | 0 | 2 | 311 | 0 |
| Suspected algaecide (copper) | 0 | 0 | 0 | 1 | 3 | 0 | 1 | 3 | 0 |
| Suspected cyanobacterial toxin(s)§ | 0 | 0 | 0 | 7 | 23 | 1 | 7 | 23 | 1 |
| Suspected norovirus | 2 | 91 | 13 | 0 | 0 | 0 | 2 | 91 | 13 |
| Suspected P. aeruginosa | 5 | 55 | 0 | 0 | 0 | 0 | 5 | 55 | 0 |
| Unidentified | 5 | 31 | 0 | 0 | 0 | 0 | 5 | 31 | 0 |
| Total (%) | 57 (70) | 1,030 (78) | 40 (65) | 24 (30) | 296 (22) | 22 (35) | 81 (100) | 1,326 (100) | 62 (100) |
Source: CDC’s Waterborne Disease and Outbreak Surveillance System, as reported via the National Outbreak Reporting System.
No deaths were reported among cases associated with these outbreaks.
Percentages do not add up to 100% because of rounding.
Confirmed or suspected cyanobacterial toxin etiologies were determined on the basis of symptom and environmental data. Microcystin was considered a confirmed etiology if water testing detected ≥20 parts μg/mL microcystin toxin in water samples collected during or within 1 day of the outbreak exposure period. Microcystin was considered a suspected etiology if water testing detected <20 μg/mL microcystin toxin in water samples collected during or within 1 day of the outbreak exposure period. All other algal toxins (e.g., saxitoxin) measured in water samples collected during or within 1 day of the outbreak exposure period were considered suspected etiologies, regardless of the toxin level. A general etiology of “cyanobacterial toxin(s)” was considered to be a suspected etiology if environmental data were insufficient to identify specific toxins or if rash was a predominant illness in an outbreak for which confirmed or suspected etiologies are not well known to cause rash (i.e., to acknowledge the potential for illness caused by undetected mixed algal blooms, exotoxins, or endotoxins).
Outbreaks with multiple etiologies are defined as outbreaks in which more than one type of etiologic agent (e.g., bacterium or virus) is detected in specimens from affected persons. Clinical test results are currently reported at the person level (e.g., five of 10 persons tested positive for Cryptosporidium) in the National Outbreak Reporting System. Clinical test results were historically reported to CDC at the clinical specimen level (e.g., five of 10 stool specimens tested positive for Cryptosporidium). Multiple etiologies were assigned when each etiologic agent was found in ≥5% of positive clinical specimens. Therefore, multiple etiology assignments presented in this report might not be directly comparable with previously published data.
Etiology unidentified: disinfection by-products (e.g., chloramines), altered water chemistry, or extremely elevated chlorine levels suspected based on reported data.