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The number of confirmed cases of the new coronavirus in the United States has risen to five, the Centers for Disease Control and Prevention said Sunday.

The five patients — all people who'd traveled recently to Wuhan, China — are in isolation at hospitals. Three cases were confirmed Sunday: one in Maricopa County, Arizona; one in Los Angeles County, California; and one in Orange County, California.

Two others were previously reported: one in Everett, Washington, and another in Chicago. All of the patients will be evaluated case by case before they're released.

Meanwhile, the number of suspected cases in the United States has been growing rapidly.

So far, about 100 samples from 26 states have been sent to the CDC for testing. Five have tested positive and 25 have tested negative; the rest are pending.

"We hold ourselves to an incredibly high standard of precision in terms of laboratory testing."

On Sunday, Dr. Nancy Messonnier, director of the CDC's National Center for Immunization and Respiratory Diseases, said doctors around the country had been calling "all day and all night" about potential cases of the respiratory illness, called 2019-nCoV.

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All testing for the new coronavirus in the United States is done at the CDC, although Messonnier said the CDC is working to get a rapid test to the states as soon as possible. The CDC has specific criteria for testing for the new coronavirus.

Suspected patients should have:

a fever

cough and/or difficulty breathing

recent travel to Wuhan, China

and/or close contact with a confirmed or suspected case of new coronavirus.

It takes about four to six hours to diagnose a case once a sample arrives at the CDC.

"We hold ourselves to an incredibly high standard of precision in terms of laboratory testing," Messonnier said Sunday in a call with journalists.

"It's always the balance of speed versus precision. And because of the sensitivity of this issue right now, we're really trying to make sure that we exercise appropriate caution in terms of development of these diagnostics," she said.

There is no evidence that person-to-person transmission has occurred anywhere in the United States.

The Los Angeles County Public Health Department said in a statement that it appears there is no threat to public health, cautioning, "People should not be excluded from activities based on their race, country of origin, or recent travel if they do not have symptoms of respiratory illness."

Cases of the new coronavirus in China have soared to nearly 2,000 in recent days. At least 56 people have died. A handful of other cases have been confirmed in other countries, including Australia, France, Japan, Singapore and Thailand.

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"Because novel coronavirus is new, we are learning more each day about transmission patterns and incubation periods," Barbara Ferrer, director of the Los Angeles Public Health Department, said in a statement. "We will keep everyone informed as more information becomes available."

Doctors are monitoring close contacts of all of the patients for at least 14 days for any symptoms. However, health officials said anyone who's had casual contact with infected patients — shopped in the same grocery store, for example — are at "minimal risk for developing infection."

"The U.S. has faced multiple pandemics before of varying degrees and severity," Messonnier said. "We need to be preparing as if this is a pandemic, but I continue to hope that it is not."

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