Norovirus Outbreak Associated With a Natural Lake Used for Recreation — Oregon, 2014

Table 1.  Demographic characteristics of cases and non-cases,* outbreak of norovirus at Blue Lake Recreational Area — Oregon, 2014

Chacteristic	Age† (yrs)		Gender§ (%)
	Median	Range	Female	Male
Cases	10	4–27	72.2	27.8
Non-cases	31	1–68	62.9	37.1

* N = 109 persons interviewed; cases are defined as persons reporting onset of illness (vomiting or diarrhea) and non-cases are defined as those persons not reporting illness.
^†p-value = 0.0002.
^§p-value = 0.45.

Table 2.  Relative risk and rates of illness from norovirus, by exposure, in persons* during outbreak of norovirus at Blue Lake Recreational Area — Oregon, 2014

Characteristic	Exposed to risk factor				Not exposed to risk factor				Relative risk model			Adjusted relative risk model			% ill persons exposed to risk factor
	Ill		Not ill		Ill		Not ill
	No.	(%)	No.	(%)	No.	(%)	No.	(%)	Risk	(95% CI)	p-value	Risk	(95% CI)	p-value
Swam	13	(54.2)	11	(45.8)	5	(5.9)	80	(94.1)	9.2	(3.6–23.4)	<0.001	2.3	(1.1–4.9)†	0.02	72.2
Used the splash pad	11	(31.4)	24	(68.6)	7	(9.5)	67	(90.5)	3.3	(1.4–7.8)	0.0039	1.4	(0.6–3.0)§	0.51	61.1
Boated	10	(71.4)	4	(28.6)	8	(8.4)	87	(91.6)	8.5	(4.0–17.8)	<0.001	1.8	(0.7–4.7)¶	0.22	55.6
Aged 4–10 years versus 11+ years	14	(28)	36	(72)	4	(6.8)	55	(93.2)	1.3	(1.1–1.6)	0.0039	1.5	(0.7–3.3)**	0.3	77.8
Drank from drinking fountain	16	(17.2)	77	(82.8)	2	(12.5)	14 5	(87.5)	1.4	(0.3– 5.4)	0.27	NA	NA	NA	88.9
Ate any food	16	(16.2)	83	(83.8)	2	(25)	6	(75)	0.6	(0.2– 2.3)	0.52	NA	NA	NA	88.9
Used the restroom	13	(16.7)	65	(83.3)	2	(8.3)	22	(91.7)	2.0	(0.5–8.2)	0.17	NA	NA	NA	86.7
Played on play structure	5	(20.8)	19	(79.2)	13	(15.3)	72	(84.7)	1.4	(0.5–3.4)	0.52	NA	NA	NA	27.8

Abbreviation: NA = not applicable; 95% CI = 95% confidence interval.
* N = 109; however, counts used to calculate measures might not add up to 109 because of missing data.
^†Controlled for boating, splash pad, and age.
^§Controlled for swimming, boating, and age.
^¶Controlled for swimming, splash pad, and age.
**Controlled for swimming, splash pad, and boating.

Authors and Disclosures

Amy Zlot, MPH¹, Maayan Simckes, MPH^1,2, Jennifer Vines, MD¹, Laura Reynolds, MPH¹, Amy Sullivan PhD¹, Magdalena Kendall Scott, MPH³, J. Michael McLuckie¹, Dan Kromer, MPA⁴, Vincent R. Hill, PhD⁵, Jonathan S. Yoder, MPH⁵ and Michele C. Hlavsa, MPH⁵

¹Multnomah County Health Department; ²CDC/CSTE Applied Epidemiology Fellowship Program; ³Oregon Public Health Division; ⁴Metro, Blue Lake Regional Park, Fairview, Oregon; ⁵Division of Foodborne, Waterborne, and Environmental Diseases, National Center for Emerging and Zoonotic Infectious Diseases, CDC.

Corresponding author
Amy Zlot, amy.zlot@multco.us, 503-988-3406.

Sidebar

What Is Already Known on This Topic?

Nationally and internationally, norovirus outbreaks have been associated with untreated recreational water venues, such as lakes. During 2009–2010, the most recent years for which finalized data are available, there were 81 recreational water–associated disease outbreaks, 24 of them associated with untreated recreational water.

What Is Added by This Report?

In July 2014, a norovirus outbreak associated with Blue Lake Regional Park in Oregon affected 70 persons. Swimming in the lake was significantly associated with illness; thus, the lake was closed for 11 days to swimming, paddleboat, and fishing activities.

What are the Implications for Public Health Practice?

Public health officials could greatly benefit from guidance for determining when to reopen untreated recreational water venues associated with outbreaks and public-facing health communication resources that promote healthy swimming and prevent recreational water–associated illness.