As the novel 2019 coronavirus case count escalates and death toll in China continues to climb, the World Health Agency declared an international public health emergency Thursday.

“Our greatest concern is the potential for the virus to spread to countries with weaker health systems which are ill prepared to deal with it,” WHO Director-General Tedros Adhanom Ghebreyesus said Thursday during an international press conference.

The declaration in Geneva came a few hours after a sixth case of the coronavirus in the U.S. was confirmed, this time a human-to-human transmission among a married couple. According to WHO, about one-fifth of patients confirmed to be infected have developed severe ailments that include pneumonia and respiratory failure.

A Chicago woman who traveled to Wuhan, China is believed to have infected her husband. Both are in stable condition at the hospital. The case makes the U.S. the fifth country where the infection has spread through person-to-person contact.

There have been no deaths in the U.S. related to the the virus, which causes flu-like symptoms and pneumonia.  In China, more than 8,200 people have fallen ill and 170 people have died, according to the latest count published Thursday by the country’s National Health Commission. The country has suspended outbound public transportation from various cities.

During the press conference, Ghebreyesus stressed that the decision was not a “vote of no confidence in China,” because the virus’ outbreak in countries outside of China is still considered to be small.

“Outside China we only have 98 cases,” he said. “If strong measures were not taken in China, this would not have happened. We have to appreciate what China is doing.”

Still, the virus’ infection rate has surpassed that of the 2003 SARS epidemic, which sickened 8,100 people within nine months.

Following suit with a national recommendation from the U.S. Centers for Disease Control and Prevention, Hawaii state health officials on Wednesday advised people to refrain from traveling to China.

Hawaii does not receive any direct flights from Wuhan, but CDC officials ramped up surveillance this week. All passengers arriving from the Hubei Province in China will be given a Travel Health Notice as they pass through Customs and Border Protection at the Daniel K. Inouye International Airport, a CDC spokesperson told Civil Beat. The Honolulu airport is one of 20 across the U.S. that has a quarantine facility, where travelers believed to be ill can be referred for a health evaluation.

Wuhan is where the severe respiratory illness is believed to have originated. Coronaviruses are typically passed from animal to human, but this one has been shown to pass among humans as well.

Reports of the virus first surfaced as a cluster of pneumonia identified on Dec. 31 and rapidly increased. About 99% of the cases have been in China, Ghebreyesus said.

Hilton Raethel, president and CEO of the Healthcare Association of Hawaii, said Wednesday that hospitals in the islands are prepared to handle any suspect cases of the virus.

“Our hospitals are well equipped,” he said. “We have isolation rooms on almost all islands in the event there is a confirmed case.”