The US Centers for Disease Control and Prevention (CDC) said Monday it had found no new cases of coronavirus but continues to investigate 110 people in 26 states for possible exposure.

Two cases have been confirmed in California. Individual cases have been confirmed in Arizona, Illinois and Washington state. All patients had recently traveled to Wuhan, center of the outbreak in China, the CDC said.

In response, the CDC said it is screening passengers on direct and connecting flights from Wuhan at five major airports: Atlanta, Chicago, Los Angeles, San Francisco and New York.

The Los Angeles Health Department said the county's only patient is receiving medical treatment and stressed that there is "no immediate threat" to the public and that "no special precautions are required." Another case was confirmed in Orange County, immediately south of Los Angeles.

A student at Arizona State University in Phoenix who recently returned from Wuhan has been diagnosed with the virus and has been isolated to prevent spread of the illness. The student did not live in a university dormitory, health officials said.

The CDC said it has sent investigators to Illinois and Washington state to check the histories of the patients and to determine if others have been exposed to the virus.

The CDC said those who have minimal contact with an infected person — such as a supermarket, movie theater or other public place — are at minimal risk of developing an infection.

This is flu season and the CDC recommends taking routine preventative actions: getting a flu shot and vigorous handwashing after going into public places or riding public transportation.

But Chinese officials said the virus may be infectious before a person develops symptoms. If so, that could make the outbreak harder to contain because there may be hidden carriers.

Severe Acute Respiratory Syndrome (SARS), killed about 600 in China and was not contagious during the incubation period, health officials said.

Worldwide, cases of the current strain of the coronavirus have been confirmed in Japan, South Korea, Nepal, Thailand, Cambodia, Singapore, Vietnam, Sri Lanka, Canada and France.

The World Health Organization (WHO) said the extent of person-to-person transmission is unclear and about 25 percent of the confirmed cases are severe. The outbreak is believed to have started in an animal market in Wuhan.

The WHO said the outbreak does not yet constitute an international public health emergency. The organization will continue to work with Chinese and health officials worldwide.

US President Donald Trump said Monday he had offered Chinese officials "any help that is necessary" to fight the coronavirus outbreak in Wuhan where about 2,800 people have been infected and at least 82 have died.

"We are in very close communication with China concerning the virus," Trump said in a tweet. "Very few cases reported in the USA, but strongly on watch. We have offered China and President Xi any help that is necessary. Our experts are extraordinary!"

On Sunday, the US State Department said it will organize a single flight out of Wuhan to evacuate diplomats and a few private citizens from the city hit hard by the coronavirus. The plane is expected to leave Tuesday and fly to San Francisco.

"The capacity is extremely limited and if here is insufficient ability to transport everyone who expresses interest, priority will be given to individuals at great risk from the coronavirus," the State Department said in a statement.

US citizens with a valid passport were advised to contact the US Embassy in Beijing. Those making the flight will be expected to reimburse the government for travel costs.

The Dow Jones Industrial Average closed Monday at 28,535.80 down 453.93 points, or 1.57 percent. The market dropped 424 points in early trading, but regained about 50 points by midday before retreating.

Oil stocks fell on fears that the outbreak could slow economic growth in China, the world's largest energy consumer. Airline, cruise and hotel stocks dropped on fears that the virus could limit global travel. Copper also fell. China is the world's largest consumer of industrial commodities. Investors bought bonds as a safe haven.

Investors will keep an eye on the Federal Reserve's announcement Wednesday on interest rates. Most analysts expect the central bank to leave the benchmark rate unchanged at 1.50 to 1.75 percent.

Bloomberg News reported that China's markets will remain closed until Feb 3 after officials extended the Lunar New Year break three days as part of the effort to contain the virus. Trading will resume next Monday in Shanghai and Shenzhen, but authorities advised that most companies shouldn't resume work until at least Feb 9.

However, China's government has imposed strict limits on travel in Hubei province where the outbreak was first reported and the CDC warned travelers to avoid Wuhan and that part of China.

Dr Paul Stoffels, Johnson & Johnson's chief scientific officer, said the drug-maker can develop a vaccine in a few months to fight the coronavirus but that it could take as much as a year to bring it to market.

"We have dozens of scientists working on this so we're pretty confident we can get something made that will work and stay active for the longer term," he told CNBC. "We'll see in the next few weeks how this goes."

The CDC recommends getting a flu shot and taking routine preventative actions such as frequent and vigorous hand-washing, especially after going into public places or riding public transportation.

The coronaviruses are named for the crown-like spikes on their surfaces. Most infections are limited to animals, including pigs and cats. In recent years, the coronaviruses have caused worldwide outbreak among humans, but officials don't know how easily the current strain of the virus is spread between people, the CDC said.

Researchers have identified seven strains of the virus known to infect humans. Most strains lead to common colds, but two are known to be deadly and cause Severe Acute Respiratory Syndrome (SARS) and Middle East Respiratory Syndrome (MERS), the CDC said.