President Donald Trump tweeted that there were only five cases of Wuhan coronavirus in the United States, hours after there was a confirmed sixth case.

Public health experts told the Associated Press that Trump's assessment of China's ability to contain the virus is optimistic.

The risk of infection for Americans is still low, public health officials told NBC Chicago.

Visit Business Insider's homepage for more stories.

After claiming to be following the novel Wuhan coronavirus outbreak, President Donald Trump tweeted that only five people were infected in the US on Thursday, hours after the US confirmed a sixth case in Chicago.

"Working closely with China and others on Coronavirus outbreak," Trump tweeted. "Only 5 people in US, all in good recovery."

The sixth case was also the first human-to-human transmission of the virus — known as 2019-nCov — in the US, as opposed to people who were already sick coming into the US. A woman in her 60's who travelled to Wuhan, China, where the outbreak began, transmitted it to her husband, according to Insider.

The infection of the husband has prompted Illinois health officials to investigate 21 more people for potential exposure to the virus, according to NBC Chicago.

However, the CDC says there is not a high risk for the public.

"This may be concerning, but based on what we know now, our assessment remains that the immediate risk to the American public is low," Robert Redfield with the CDC told NBC Chicago.

The Trump administration announced a task force dedicated to the coronavirus. And according to the Associated Press, Trump (who has described himself as a "germaphobe") has called in the small number of cases in the US a "very little problem," and is optimistic that the US could keep the spread "under control."

Other confirmed cases in the US were reported in Washington state, California, and Arizona. The virus has spread to 20 countries and infected over 9,700 people and killed more than 213 worldwide.

Local officials in all six cases reported the patients were in isolation, but no report no official report has been given on their recovery status.

The Center for Disease Control reported at least 165 people from 36 states have been or are waiting to be tested for the virus, and as of Wednesday 68 have turned up negative.

The coronavirus is thought to have originated in Wuhan, China. Despite China's unprecedented quarantine of nearly 50 million citizens in 16 cities, the coronavirus has spread.

While Trump has said he believes China is handling the outbreak, public health experts have disagreed.

"China manifestly does not have this under control," Lawrence Gostin, a professor of global health law at Georgetown University told the AP, citing how slowly decisions were made by Chinese officials, which allowed for thousands of people to leave Wuhan aiding the spread of the virus.

On Thursday, The World Health Organization declared the outbreak a "public-health emergency of international concern."