Testing at Cascade Locks School confirmed that the December outbreak was caused by a Norovirus GII.
The Oregon State Public Health Lab is currently doing gene sequencing to determine the exact strain, according to Tracy Willett, Hood River County Health Officer.
Human noroviruses are the major cause of acute nonbacterial gastroenteritis and the leading cause of outbreaks of gastroenteritis worldwide, Willett said in a press release.
Willett said it is unknown how many people in Hood River County had been affected by norovirus as reporting is not required. About half the student body of Cascade Locks School was absent during a week-long period in early December, leading the school district to sterilize the school overnight on Dec. 17.
Oregon has seen about twice the number of norovirus-like outbreaks since November 2012 as in the same time in 2011. Norovirus outbreaks occur mainly in the winter months.
On Nov. 26, the Centers for Disease Control and Prevention announced that a new strain of norovirus was identified in Australia and has reached U.S. shores. Genotype II-4 (GII.4) norovirus spreads rapidly and is the most commonly detected strain worldwide. This new strain, norovirus GII.4 Sydney, was confirmed in Oregon by the Oregon State Public Health Laboratory on Dec. 10.
The arrival of a new strain — i.e., the arrival of a new strain to which no one is immune — occurs about every four years and usually, but not always, results in widespread illness in the community, according to Willett.
Noroviruses can be transmitted by accidentally ingesting the virus, which is present in stool or vomitus. This usually happens by eating food or drinking liquids that are contaminated with norovirus, touching surfaces or objects contaminated with norovirus then putting your fingers to your mouth, or having contact with someone who is infected with norovirus (for example, caring for or sharing food or eating utensils with someone with norovirus illness).
The average incubation period for norovirus-associated gastroenteritis is 12-48 hours. Symptoms include nausea, vomiting and watery, and non-bloody diarrhea with abdominal cramps.
In addition, myalgia, malaise and headache are commonly reported. Low-grade fever is present in about half of cases. Dehydration is the most common complication and may require intravenous replacement fluids. Symptoms usually last 24-60 hours. In up to 30 percent of infections, the carrier may experience no symptoms.
Willett said norovirus is very, very contagious. Precautions include washing affected surfaces with dilute bleach solution (one part bleach to 10 parts water), using warm water and soap for hand-washing, and having ill people use their own dishes and, if available, a separate bathroom.
People who have been ill should stay home for 72 hours after symptoms disappear to limit spread.