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

Amy Zlot, MPH; Maayan Simckes, MPH; Jennifer Vines, MD; Laura Reynolds, MPH; Amy Sullivan PhD; Magdalena Kendall Scott, MPH; J. Michael McLuckie; Dan Kromer, MPA; Vincent R. Hill, PhD; Jonathan S. Yoder, MPH; Michele C. Hlavsa, MPH

Disclosures

Morbidity and Mortality Weekly Report. 2015;64(18):485-490.

Laboratory Testing

Five ill persons provided stool specimens, which all tested positive for norovirus genogroup I by polymerase chain reaction. These specimens also tested negative for Salmonella, Shigella, Escherichia coli O157:H7, and Campylobacter.

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Table 1. Demographic characteristics of cases and non-cases,* outbreak of norovirus at Blue Lake Recreational Area — Oregon, 2014
Chacteristic	Age^† (yrs)		Gender^§ (%)
Chacteristic	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		Relative risk model			Adjusted relative risk model
	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.