True number of US coronavirus cases is far above official tally, scientists say

An analysis of the novel coronavirus's spread inside the United States suggests that thousands of Americans are already infected, dimming the prospects for stomping out the outbreak in its earliest stages.

Researchers estimate that by March 1, the virus had already infected about 1,000 to 10,000 people who have not yet been accounted for. At the start of this month, about 80 U.S. cases had been confirmed and officials were still expressing confidence they could contain the new virus.

Quarantines, contact tracing and other public health measures have likely tamped down the COVID-19 outbreak here, the researchers said. But from the start, a group of infected travelers just big enough to fill an elevator likely has been expanding the virus's reach, largely undetected.

Released into a country of about 330 million, each of these travelers was assumed to have passed the virus to 2 to 2.5 people, each of whom in turn infected another 2 to 2.5 people, and so on. Tote up the nodes on this rapidly branching network of contacts and the number of victims balloons quickly, the researchers wrote.

Their study, released Monday on the medRxiv website to discuss work that has not yet been submitted to a peer-reviewed journal, came as U.S. officials reported a total of 704 COVID-19 cases and 29 deaths in the United States. That is likely just the tip of a much larger iceberg, the mathematical modeling suggests.

Under their most optimistic assumptions, as few as 1,043 people in the United States have been infected with the novel coronavirus. Under a more realistic scenario, that number could easily be as high as 9,484.

That only accounts for U.S. residents whose infections originated with people carrying the virus directly from Wuhan, the epicenter of the outbreak in China. In reality, many more people likely have brought the virus here from other hot spots, including Italy, South Korea and the rest of Asia. Each virus carrier who arrived from those places would set off his or her own cascade of infections.

The model also stopped adding up infections as of March 1. But given its firm toehold in the United States by then, the virus could have racked up tens of thousands of new cases since that date.

The mathematical simulation of the U.S. outbreak was run over a thousand times by a team from Cedars-Sinai Medical Center in Los Angeles and Peking University in Beijing. They began with a hypothetical group of undetected carriers -- likely eight to 16 people -- who arrived in the United States on direct flights from Wuhan after the virus now known as SARS-CoV-2 began infecting humans in late November but before those flights were halted on January.

It's safe to assume that roughly half of these travelers were intercepted by U.S. health officials and saw their movements curtailed. The rest continued on their journeys with their undetected infections, each setting off an unrecognized chain of transmission.