By Robert Preidt, HealthDay Reporter

MONDAY, March 9, 2020 (HealthDay News) -- More than 9,000 people in the United States may have been infected with the new coronavirus as of March 1 -- a figure much higher than reported, researchers say.

"This suggests that the opportunity window to contain the epidemic of COVID-19 in its early stage is closing," said investigators at Cedars-Sinai in Los Angeles.

Since most cases of COVID-19 appear to be mild or even without any symptoms, the researchers noted it can make it difficult to identify infected individuals who may be spreading the virus.

Photos: The Coronavirus Hits the U.S. View All 14 Images

The investigators said they chose "very conservative" methods to estimate the number of coronavirus cases. "This makes our current estimation [of more than 9,000] likely to be an underestimation of the true number of infected individuals in the U.S.," they wrote in a medical center news release.

Their paper has not been peer-reviewed and should be considered preliminary until that time. It's posted online on a forum where physicians and researchers share information.

"We are making the results public before peer review as it will be important for timely and informed public health decision-making. We are also making the model available to the research community so that others can build upon it," said study first author Dalin Li. He's a research scientist in the Inflammatory Bowel and Immunobiology Research Institute.

As of Saturday, the U.S. Centers for Disease Control and Prevention website reported 164 confirmed and presumptive cases in the United States. However, on Sunday, most media reported more than 500 cases in the country.

For this study, the researchers considered only COVID-19 cases "imported" directly into the United States from the area of Wuhan, China, before Jan. 23. That's when the Chinese government locked down the city where the outbreak began.

Based on their computer modeling, the researchers estimated the total number of people in the United States infected with coronavirus as of March 1 to be between 1,043 and 9,484.

The first figure assumed that current preventive procedures such as quarantining and screening international travelers at airports had reduced transmission of the virus by as much as 25% in unidentified cases. The second figure assumed no preventive measures had been undertaken.

The difference between the lowest and highest estimates is important when it comes to slow the spread of the coronavirus, according to study senior author Dr. Dermot McGovern, professor of medicine and biomedical sciences at Cedars-Sinai.

"Our model suggests that even moderately effective population interventions to reduce transmission can have a profound impact on the scale of the epidemic," McGovern said. "This finding supports the role of public health interventions in controlling this disease."

Those measures include social distancing to keep people from interacting too closely or frequently, personal hygiene, and restricting large gatherings for events such as sports.

More information

The World Health Organization has more on COVID-19.