Centers for Disease Control and Prevention Director Robert Redfield arrives to brief senators
Centers for Disease Control and Prevention Director Robert Redfield arrives to brief senators during a closed all-senators briefing on the coronavirus on Capitol Hill in Washington, Jan. 24, 2020.

WASHINGTON - U.S. health officials are urging China to share more information on how the novel coronavirus that emerged in Wuhan is spreading.

The virus has sickened more than 5,974 people in 18 countries, mostly in China.  Chinese health authorities announced an additional 26 deaths Tuesday, bringing the total to 132.

Chinese experts have reported the virus can spread from patients who are not showing symptoms. But U.S. health officials say they are withholding judgment.

"CDC has not been given the opportunity to review that data," said Centers for Disease Control and Prevention Director Robert Redfield at a press conference Tuesday. "The Chinese believe they have that data. This is our hope, to be able to review and be more definitive."

WATCH: US Calls on Beijing to Allow More Public Health Experts into China

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If patients are spreading the virus without showing symptoms, that calls for different screening procedures, added National Institute of Allergy and Infectious Disease Director Anthony Fauci.

Fauci said asymptomatic patients are unlikely to have much impact on the spread of the disease.

"In all the history of respiratory borne viruses of any type, asymptomatic transmission has never been the driver of outbreaks," he said. 

Health officials have identified five cases in the United States and no person-to-person transmission so far. Redfield said the risk to Americans currently is low, but he expects more cases are coming.

Passengers wear protective face masks arrive at the high speed train station in Hong Kong, Jan. 28, 2020. Hong Kong's leader has announced that all rail links to mainland China will be cut starting Friday.

Ready, willing and able

The United States has offered to send experts to China to assist with the outbreak, but Health and Human Services Secretary Alex Azar said Beijing has not accepted the offer.

"CDC experts are standing by, ready, willing and able, to go to China either on a bilateral basis or under the auspices of the World Health Organization," he said.

WHO announced in a statement Tuesday that the organization "will send international experts to visit China as soon as possible." 

"The posture of the Chinese government, levels of cooperation, and interaction with us is completely different from what we experienced in 2003," when officials covered up the emergence of severe acute respiratory syndrome (SARS), a disease that killed nearly 800 worldwide, Azar said. "I want to commend them for that."

However, he said, "we are urging China, more cooperation and transparency are the most important steps you can take toward a more effective response."

Hong Kong Chief Executive Carrie Lam, left, wears a protective face mask speaks during a press conference held in Hong Kong, Jan. 28, 2020.

Countermeasures

There is no approved treatment for coronavirus infection, but Fauci said several are under study, including drugs that have shown some effectiveness against Ebola and HIV.

A vaccine is in the works, as well. Fauci hopes to begin initial tests within the next three months.

He cautioned, however, that "going into a Phase One trial does not mean that you have a vaccine that's ready for deployment." It will take several months to determine whether the vaccine is safe and can proceed to further tests. He noted that by the time results came in from a Phase One SARS vaccine trial, the outbreak was already under control.

Health officials are now screening travelers from China at 20 U.S. airports. 

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