All people who have been in close contact with nCoV infections need to be tested, even if there are no symptoms, US health officials say.

"Since infection in the absence or absence of symptoms is a serious problem, the new guidelines will increase the requirement for asymptomatic people testing, including those who have been in close contact with nCoV infection," said

The change comes after the CDC received many criticisms of the guidelines last month, which stated that people who have had close contact with someone with Covid-19 do not necessarily need to be tested if there are no symptoms.

Public health experts support the CDC change when it comes to research that shows that asymptomatic people have a huge potential for public infection.

"It's good to see science and real-world evidence playing a key role in change," said Scott Becker, executive director of the Association of Community Health Laboratories.

"I am delighted to see this change and obviously this is what needs to be done," said Dr. Ashish Jha, principal of Brown University's School of Public Health.

The old guide, released on August 24, led to a wave of harsh criticism from the scientific community and CDC partners, including the Infectious Diseases Association of America, which has urged their members to continue.

"Returning to the science-based approach to providing CDC testing guidelines is good news for public health," said Dr. Thomas File, the association's president.

Studies have shown that people can infect the virus even without symptoms.

After facing criticism from the scientific community, CDC director Robert Redfield last month tried to clarify the agency's position by saying that testing "could be considered" for asymptomatic infected people.

The United States, the world's largest epidemic zone, has reported nearly 7 million infections and more than 203,000 people died of Covid-19 since the outbreak.