This article was originally posted on RealClearScience.
Please, take a seat. We need to talk about norovirus. (If you have norovirus, you’ve probably already taken a seat… on the toilet.)
By now, you’re familiar probably with the story: Thousands of eager vacationers board a cruise ship to somewhere exotic in the Caribbean. On the way, the passengers acquire something exotic, and hundreds of them begin to expel fluids from both ends of their digestive tracts. The culprit is often the infamous norovirus. But, what is norovirus, and where did it come from?
The story of norovirus begins in 1929, when the first suspected cases occurred. But it wasn’t until 1968 that we had a better idea of what we were dealing with. That year, there was an outbreak in a school in Norwalk, Ohio — the city from which the virus derives its name. Epidemiologists took stool samples from infected adults and removed all of the bacteria. They then fed these samples to volunteers (yes, seriously), who became sick. A couple of years later, viral particles were observed microscopically.
Norovirus is a small, RNA virus. (Unlike most other organisms, viruses can have RNA genomes.) The tiny bug is only about 33 nanometers in diameter. To put that size into perspective, consider that the unaided human eye cannot see anything smaller than about 0.06 millimeters. Therefore, you would have to line up more than 1,800 viruses end-to-end before your eye might have a chance of seeing them.
They are incredibly infectious. The average person needs to come into contact with just 18 of these little viruses to become sick. Compare that number to say, Salmonella, which may require about 100,000 bacterial cells to cause illness. That explains why hundreds of people on cruise ships get sick. The virus can be spread in feces or vomit, and if an infected person doesn’t adequately wash his hands or change his clothes, it takes only a tiny number of viruses to infect somebody else. Buffet lines, common bathrooms, and doorknobs all become potential sources of infection.
But cruise ships aren’t the only places you will find norovirus. In fact, norovirus infection is quite common. About 20 million Americans become infected every single year, and worldwide, the virus kills 200,000 children under the age of five. Living in our plush society, we tend to forget that diarrhea is lethal in many poor parts of the world.
So, if you do become sick — and odds are you will — be thankful you live a country that has good medical care.
Source: MV Yates et al. (2014). Microbiology of Waterborne Diseases (2nd ed). London: Elsevier Academic Press.