Norovirus — the scourge of the cruise ship and, lately, the Pyeongchang 2018 Olympic Winter Games. The incapacitating and vaccine-less virus is known to spread from person to person, and it has long been suspected that people can also catch the illness from touching contaminated surfaces.
A study by Arizona State University applied mathematicians in Royal Society Open Science, tracked the different ways that norovirus spreads, and which one infects the most people. They refined their model by fitting it to data from a real-world outbreak — in this case, the daily number of cases among crew and passengers over the course of two cruises.
“The data from the two groups gave the model the sensitivity it needed to be able to figure out the relative roles of infected surfaces and people in transmitting the illness,” said Sherry Towers, the study’s lead author and professor at the Simon A. Levin Mathematical, Computational and Modeling Sciences Center.
“The findings indicate that, although environmental transmission by itself is enough to keep an outbreak going, person-to-person contact is the primary mode of transmission,” Towers said.
This explains why densely populated environments with large common areas like cruise ships, resorts and Olympic villages are the perfect settings for wide-scale outbreaks. But knowing that personal contact is the main way the disease spreads also provides a solution.
What preventative measures work?
Because aggressive steps like self-quarantine and avoiding people who are already infected often happen too late — or not at all — in these environments, the team’s next step was to compare the effectiveness of different preventative measures, such as hand washing and surface cleaning, in halting the spread.
“It only takes a few virus particles to make you sick, so no matter how stringent the cleaning, it is next to impossible to remove all the virus from contaminated surfaces,” Towers said. “However, since the primary route for infection is hand-to-mouth contact, you can’t be infected if you wash your hands thoroughly before eating or touching your face.”
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