June 8 (UPI) -- At least seven strains of the new coronavirus have been circulating in California since the COVID-19 outbreak in the United States started, an analysis published Monday by the journal Science has revealed.
The findings suggest that the cases of the disease, caused by SARS-CoV-2, likely originated from several sources, including not only overseas travelers but also from visitors from other states -- like Washington -- as well, the authors said.
"While the sample size is small, this study suggests that there may have been multiple introductions of the virus into the United States," Brandon Brown, an associate professor of social medicine population and public health at the University of California-Riverside, told UPI.
"The findings may actually leave us with more questions than answers regarding the introduction of SARS-CoV-2 in the U.S.," said Brown, who was not part of the Science analysis.
Through Monday afternoon, 1.95 million confirmed cases of COVID-19 have occurred in the United States, according to Johns Hopkins University. To date, California has had roughly 129,000 of them, based on data from county public health departments.
For the Science study, conducted by a team of California public health officials and international researchers, researchers analyzed viral samples from 36 patients spanning nine counties and the Grand Princess cruise ship. The ship docked in San Francisco Bay in March after an outbreak occurred on board.
The analysis revealed the introduction of at least seven different SARS-CoV-2 lineages into California, including epidemic WA1 strains associated with Washington State, the authors said.
There was no "predominant lineage" and limited transmission between communities within the state, they added.
In general, the findings "support contact tracing, social distancing and travel restrictions to contain SARS-CoV-2 spread in California and other states," the authors said.
"Initially, we were focused on preventing the introduction of the virus via travel, but we soon began to understand the prevalence of the virus in the community among those who had not traveled," Brown said.
"This study does illustrate the potential multiple introductions of the virus into Northern California, which makes it more difficult to control the spread," Brown said.