A notice showing "facial masks are out of stock" is seen on a door of a pharmacy in New York, the United States, Feb. 29, 2020. (Xinhua/Wang Ying)

US researchers said the novel coronavirus may have been spreading in the Washington state for six weeks after they examined the genomes of two infections in the state, the New York Times reported on Sunday.

Trevor Bedford, an associate professor at the Fred Hutchinson Cancer Research Center and the University of Washington, said those two people live in the same county but are not known to have had contact with one another.

The genetic findings suggest that the virus has been spreading through other people in the community for nearly six weeks, according to Bedford.

One of the two cases was reported on Jan. 20 while the other announced on Friday. The latter was more likely to be descended from that first case since in both cases the virus contained a genetic variation that appears to be rare. It was found in only two of the 59 samples whose sequences have been shared from China, according to Bedford.

"It's extremely unlikely that two viruses coming from outside the USA. independently would arrive in the same geographical area and be genetically related unless they were connected," said Andrew Rambaut, professor of molecular evolution at the University of Edinburgh, who was not involved in the analysis.

Mike Famulare, a principal research scientist at the Institute for Disease Modeling in Bellevue, Washington state, participated in the analysis. He said if the virus has been spreading undetected in Washington since mid-January, that could mean that anywhere from 150 to 1,500 people may have it, with about 300 to 500 people being the most likely range.

The figure is a "best guess, with broad uncertainty," Famulare added.

Those people "have either been infected and recovered, or currently are infected now," Famulare was quoted as saying.

As of Sunday, a total of 43 cases have been detected and tested in the United States through US public health surveillance systems, including 17 travel-related ones and 26 who did not travel and did not have known contact with other infected people.