The U.S. Centers for Disease Control and Prevention (CDC) is focusing much of its coronavirus containment effort on screening close contacts of those who may have been exposed to the disease in China—and is bracing for further spread to these individuals in the weeks to come, according to a report released Feb. 7.

The CDC in January tested 210 people in the U.S. for a novel coronavirus, known as 2019-nCoV, that originated in Wuhan, China and has infected about 31,500 people worldwide as of 1:30 p.m. Friday. Only 5% of the people tested in the U.S., or 11 individuals, tested positive for 2019-CoV, according to the new report. (A 12th case has since been confirmed.) The tested individuals ranged in age from 21 to 49, and all of them had symptoms including fever, cough, shortness of breath or upper respiratory tract issues such as a sore throat.

About 20% of the individuals tested had not traveled to China themselves, but had instead spent time with a sick person who tested positive for, or was suspected to have, 2019-CoV; another 9% had both traveled to China and been in touch with those who had. So far, two people in the U.S. have gotten sick after their spouse contracted the coronavirus in China.

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As its investigation continues, the CDC says it expects close contacts of sick individuals to make up a larger proportion of suspected coronavirus cases, especially since travel restrictions have been implemented throughout Asia. The U.S. has also taken precautions of its own, including quarantining people who were evacuated from China and flown back to the U.S., and temporarily refusing entry to foreign nationals who have visited China.

The CDC’s latest report also suggests that Americans have been following directives to seek medical care if they develop symptoms of coronavirus, including cough, fever and difficulty breathing. Only six people tested for coronavirus were identified through airport screening, while 26 people were found by specifically looking for contacts of sick individuals. The remaining 178 were identified in a hospital, health clinic or other medical office, presumably after choosing to seek care.

Many people tested by the CDC turned out to have another respiratory illness, such as the seasonal flu. Given the similarity between the two illnesses, the CDC has advised that people minimize the spread of coronavirus much as they would during any winter illness season: by washing their hands, covering coughs and sneezes and staying home when they feel sick.

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Write to Jamie Ducharme at jamie.ducharme@time.com.