May 9, 2012 -- A new study shows just how easy it is to catch norovirus, the fast-spreading stomach bug that's famous for causing misery on cruise ships.
The study tracked a 2010 outbreak of norovirus among young soccer players in Oregon. Seven out of 17 players who attended an out-of-state tournament fell ill with severe vomiting and diarrhea, but curiously, none of them had been in direct contact with the index case -- the first girl to get sick.
Investigators were stumped.
"We conducted a very extensive interview; it's called a shotgun interview, where we ask about every possible food exposure. There are over 800 questions on the questionnaire," says Kimberly K. Repp, PhD, an epidemiologist with the Washington County Department of Health and Human Services in Hillsboro, Ore.
That helped the researchers figure out what the sick people ate and what the healthy people didn't eat.
The common denominator? Cookies. All the girls who got sick had eaten cookies during a Sunday lunch. By Tuesday, they'd all fallen ill.
Grocery Tote Carried More Than Food
Norovirus is the leading cause food-borne illness in the U.S. But because the cases were isolated to this relatively small group, rather than widely reported by many people who ate the pre-packaged snacks, researchers didn't think the cookies themselves were the source.
"It was something about the cookies, we knew, that was associated with the source of the outbreak," Repp says.
The connection turned out to be a reusable grocery tote bag filled with the cookies and other food items like chips and grapes that had been sitting on the floor of the bathroom where the first girl had repeatedly gotten sick.
The study describes the bag as a reusable open-top grocery bag made from laminated woven polypropylene, a common type you might buy at many grocery stores these days for repeat use.
Investigators swabbed the bag two weeks after the first person fell ill. DNA tests turned up copies of the same strain of norovirus that had infected the girls.
"This is the first-ever reported case of transmitting this virus with an inanimate object, basically," Repp says.
The study is published in the Journal of Infectious Diseases.
The first sick girl said she never touched the bag. So how did the virus get there?
Experts say viral particles likely floated over from the toilet.
"That certainly is an area of active research, involving the dynamics of vomiting, and how are particles dispersed when somebody vomits. There is a limited range, for sure, but exactly how far it is and what the level of risk is 10 feet away or 30 feet away. Certainly, in this case, it was plenty close to allow the virus to float over onto the bag," says Aron J. Hall, DVM, MSPH, of the CDC's division of viral diseases.
Disinfect Surfaces After Someone Gets Sick
In an editorial on the study, Hall says that it takes as little as 18 copies of a norovirus to make someone sick.
"It's among the most infectious viruses known to man," Hall tells WebMD.
"The amount of virus that it would take to get someone sick certainly cannot be seen with the naked eye, and definitely underscores the challenge of removing all potentially infectious virus from a grocery bag, in this case, or a bed rail in a hospital, or a doorknob in a nursing home," he says.
Researchers say the study highlights how easily the virus can travel and how long it can persist on the surfaces where it lands.
"This is a really underestimated route of transmission, and it's easy to fix," Repp says. "I don't know about you, but when I'm done with my clothes, I wash them when they're dirty. We should probably be washing our reusable bags, too."
According to the CDC, chlorine bleach is one of the few household cleaners that can kill norovirus. The agency recommends using 5 to 25 tablespoons of bleach per gallon of water to clean and disinfect contaminated surfaces.
"When cleaning an area after someone is ill, we need to not just be thinking about wiping down the toilet area. We need to think about the virus up in the air and landing on everything in that bathroom, and either throwing away or cleaning everything that was exposed," Repp says.