SLATE: Passengers on Royal Caribbean’s Explorer of the Seas came home two days early this week after more than 600 people fell ill with suspected norovirus, also known as Norwalk disease. Norovirus loves a good cruise ship, with its tight quarters full of people from all over the world. There have been nearly 200 confirmed norovirus outbreaks on cruise ships in the past 20 years, plus many other suspected maritime norovirus outbreaks that couldn’t be definitively linked to the virus. But it isn’t an exclusively sea-going pathogen. It accounts for more foodborne illness in the United States than E. coli and salmonella combined. It lives on doorknobs, handrails, and even soft surfaces like couches and carpets. Norovirus is all around you. And it is sickening more people than ever. It is a wondrous pathogen that should fascinate, disgust, and frighten you in equal measure.
Most viruses are encased by a lipid envelope, which has a couple of vulnerabilities. First, it dries out when exposed to the elements, which is one of the reasons HIV, for example, dies almost immediately outside of a host. In addition, alcohol-based sanitizers easily penetrate a lipid envelope and destroy the virus. Norovirus has a protein shell with no such weaknesses. It can live in the open for weeks and possibly months, and it is resistant to hand sanitizer and soap, unless you scrub the heck out of it. When a cruise ship suffers an outbreak, the Centers for Disease Control and Prevention advises that virtually every inch of the vessel and everything on it be drenched in a 5-percent bleach solution. Since schools, concert halls, movie theaters, and private homes rarely undergo such a thorough scrub-down, it’s disturbing to imagine how often we encounter norovirus. (If you decide to bleach your house after your child falls ill, it’s better to go with a 10-percent solution, since bleach degrades rather quickly in a bucket.)
The situation is all the more worrying when you consider norovirus’ second neat trick—it takes an incredibly small number of viral particles to make you sick. Most pathogens, such as influenza, need to invade you with an army of thousands to cause symptoms. That’s one of the reasons we’re generally healthy in a world teeming with viruses. Mathematical modeling suggests that as few as 10 norovirus particles can make an adult sick. The average norovirus virion is around 35 nanometers across—one-third the size of most viruses—so the volume of an infectious dose is uniquely small. It can easily find its way into your mouth through your hands or a whiff of infected air… (more)
