Story at a glance
- The study says undocumented infections were the infection source for 79 percent of documented cases.
- If undiagnosed patients hadn’t spread the virus, the number of cases could have been reduced by 66 percent in Wuhan and 79 percent across China.
- The study underscores the need for widespread testing.
A new study estimates 86 percent of COVID-19 infections in China went undiagnosed before the country enforced a travel ban in late January, leading to the rapid spread of the virus.
Researchers behind the study published in Science Monday used mathematical models to simulate the outbreak and calculated the contagiousness of people who were reported to have the COVID-19 virus and the estimated number of undocumented cases.
The study found that undocumented cases transmitted the virus about half as often as documented cases, but there were significantly more undocumented cases. Researchers said those who were not diagnosed were the source of about 8 out of every 10 infected cases in China before Jan. 23.
“It’s the undocumented infections which are driving the spread of the oubtreak,” Columbia University’s Jeffrey Shaman, a co-author of the study, said according to GeekWire.
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Those who are not diagnosed often experience mild symptoms or none at all, leading these patients to “expose a far greater portion of the population to the virus than would otherwise occur,” the study said.
Researchers estimate that if the virus among undiagnosed people had not spread, the amount of cases may have been reduced by 66 percent in Wuhan, the city at the epicenter of the outbreak, and by 79 percent across China.
“More active testing procedures would catch more cases,” Shaman said. “How that would be implemented is something that we can debate for quite some time. And obviously this all has to be done under the backdrop of the logistics and costs of implementing lots more tests.”
In the United States, health officials are urging people to stay home to stop the spread of COVID-19, and some cities like San Francisco, have implemented shelter-in-place orders as widespread testing lags.
More than 6,500 cases have been confirmed in the U.S. with at least 115 deaths.
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