The Centers for Disease Control and Prevention (CDC) said Thursday that an Illinois woman who recently returned from China has transmitted the coronavirus to her husband — the first known case of person-to-person spread of the virus in the United States.

The 61-year-old woman had traveled to Wuhan, center of the outbreak in China. She returned to the US on Jan 13 and soon developed symptoms of infection, including fever and shortness of breath. Her husband hadn't recently traveled outside the US. Both have been hospitalized and are reported in good condition.

Chicago health officials said the woman limited her movement outside her home after returning to the US and didn't take public transit or attend large gatherings with her husband.

"We know coronaviruses are most likely to spread through close personal contact, and we know this second patient had close contact with his wife after she began to develop symptoms, so it's not totally unexpected that he acquired the virus," Allison Arcady, commissioner of the Chicago Department of Public Health, told reporters Thursday at a news conference.

She said public health officials followed standard procedures after the wife reported symptoms and closely monitored her husband. After being diagnosed, both were isolated to reduce the risk of the virus spreading.

"This is exactly why public health has been monitoring him closely, and why we monitor any close contacts of confirmed cases. This does not change our guidance that the risk to the general public remains low at this time,'' Arwady said. "People in the community do not need to change their behavior based on this news. For example, they don't need to cancel events, avoid mass gatherings, or wear gloves and masks in public."

The woman's husband is the second person to be diagnosed with the virus in Illinois and the sixth confirmed case in the US. Health officials said 21 Illinois residents are being monitored for possible exposure to coronavirus.

"It hasn't changed anything we're doing," Scott Pauley, a spokesman for the CDC in Washington, told China Daily.

Dr Ngozi Ezike, director of the Illinois Department of Public Health, said officials will continue to monitor those who came in contact with the original patient.

"While there is concern with this second case, public health officials are actively monitoring close contacts, including health care workers, and we believe people in Illinois are at low risk," he told reporters.

In Indiana, which borders Illinois to the east, state health department officials and the CDC issued a statement Tuesday saying they had identified a person who may be infected with the coronavirus.

"Final diagnosis awaits the results of laboratory tests performed by the CDC," the joint statement said. "Out of an abundance of caution, the individual has been placed in isolation and is currently under active medical supervision."

Health officials hope transmission of the coronavirus doesn't spread beyond travel-related cases and their immediate families. If it doesn't, health officials believe they have a good chance to limit the spread of the virus in the US.

Continued transmission of the virus from one person to another among strangers rather than family members would be much more difficult to contain.

Through Thursday, health officials worldwide have reported 9,692 infections stemming from the novel strain of the coronavirus. Most have occurred in China, where the coronavirus has been blamed for the deaths of 213 people.

Worldwide, there have been about 70 reported cases in 15 countries outside China, but no deaths.

"We understand this may be concerned, but based on what we know now, our assessment remains that the immediate risk to the American public is low," Robert Redfield, CDC director, said Thursday in Washington.

The CDC recommends basic steps to avoid contracting the virus, including washing hands with soap and water for at least 20 seconds. If soap is not available, the CDC recommends an alcohol-based hand sanitizer that contains at least 60 percent alcohol. The CDC said everyone should avoid touching their nose or mouth with unwashed hands.

The CDC said there is no specific anti-viral treatment recommended for the new strain of the virus. Development and distribution of a vaccine could take as long as a year.