15th novel coronavirus patient reported in the US

China's Hubei province reported a nearly tenfold increase in cases on Thursday.

A 15th patient has been diagnosed with novel coronavirus in the United States, health officials reported Thursday.

The patient was among the Americans repatriated from Wuhan, China, the epicenter of the new coronavirus outbreak, and had been quarantined at Lackland Air Force Base in San Antonio, Texas.

That group's 14-day quarantine period is scheduled to end Feb. 20 and quarantined passengers are being monitored, including having their temperature taken twice daily.

Health officials warned that there may be additional cases that emerge among the repatriated Americans at Lackland but stressed that risk to the greater community is low.

"San Antonians should feel confident and continue to go about their lives," Mayor Ron Nirenberg said at a Thursday news conference.

In Washington, Health and Human Services Secretary Alex Azar addressed Congress Thursday, maintaining that the administration takes the thread of novel coronavirus seriously.

To that end, the CDC is working with health departments in five cities "to use its flu surveillance network to begin testing individuals with flu-like symptoms for the coronavirus,” Azar said.

Japan reports coronavirus death, China changes how cases are diagnosed

Meanwhile, a second novel coronavirus death outside of China was reported in Japan, the country's health minister announced Thursday.

The patient, a woman in her 80s, had been hospitalized in Tokyo since early February, after she developed symptoms of the virus. The only other death from the outbreak outside of China occurred in the Philippines. There has also been a death in the semi-autonomous Chinese city of Hong Kong.

The Chinese province at the heart of the novel coronavirus outbreak reported a nearly tenfold increase in cases on Thursday morning after applying new methodology to how cases are categorized.

The Health Commission of Hubei Province announced an additional 14,840 cases of the newly identified virus, known officially as COVID-19, as well as 242 more deaths.

The commission explained in a press release that the record spike was due to a change in how cases are diagnosed and counted, with the total number of confirmed cases now including "clinically diagnosed cases," or patients who showed symptoms of the disease and were diagnosed through CT scans of the lungs, for instance, but have not yet had laboratory testing.

The expanded criteria is meant to ensure "that patients can receive standardized treatment according to confirmed cases as early as possible to further improve the success rate of treatment," the commission said.

"We need to be cautious when drawing conclusions from daily reported numbers," Dr. Mike Ryan, executive director of WHO Health Emergencies Program, said during a Thursday press briefing. Because the cases from China are being retrospectively reported, the overnight increase in shouldn't be considered a spike, he said.

"We need to be very careful when reporting any extremes," he added.

The overall number of cases in China now stands at 59,882, with 1,368 deaths, including one in the semi-autonomous city of Hong Kong, according to the Chinese National Health Commission. Roughly 80 percent of those cases have been reported in central Hubei province, with the epicenter of the outbreak in its capital, Wuhan, where the first cases were detected last December.

There are at least 441 cases confirmed in 24 other countries, according to the World Health Organization, which has declared the outbreak a global health emergency.

So far, there are only 15 cases confirmed in the United States, according to the U.S. Centers for Disease Control and Prevention. The patients are in Arizona, California, Illinois, Massachusetts, Washington, Wisconsin and Texas and all but two cases are linked to travel to Wuhan, China.

The novel coronavirus causes symptoms similar to pneumonia, ranging from mild, such as a slight cough, to more severe, including fever and difficulty breathing, according to the CDC. There is no vaccine yet for the virus, nor any known effective therapeutics.

More new infections among Diamond Princess cruise ship passengers

Meanwhile, the number of people infected with the virus aboard a quarantined cruise ship in Japan continues to tick upward. Since the Diamond Princess arrived at the Japanese port of Yokohama on Feb. 3, at least 218 people on board have tested positive for the new coronavirus by Thursday morning -- with 44 new cases in the past 24 hours. At least one quarantine officer has also been infected, according to Japan's Ministry of Health, Labor and Welfare.

The uptick in cases makes the vessel the largest center of infection of anywhere outside of China.

All those infected with the disease on the Diamond Princess have been brought ashore for treatment, while the other passengers have been confined to their rooms on board as the ship remains quarantined at sea.

However, Japan's Ministry of Health, Labor and Welfare announced Thursday its plans for a voluntary disembarkation of guests to complete their quarantine period at a shoreside facility.

A spokesperson for Princess Cruises, which operates the ship, said "it is our understanding that this will be a phased approach, with the most medically vulnerable guests in the first phase, including older adults with pre-existing health conditions."

"According to officials, guests in the first group will be tested for the 2019 novel coronavirus," the cruise line spokesperson said in a statement Thursday. "If the test is positive, they will be transported to a local hospital for further evaluation and isolation. If the test is negative, they will be given the option to leave the ship and be transported to a quarantine housing facility."

All guests aboard the Diamond Princess "remain welcome to stay on board through the end of the quarantine period," the spokesperson added.

The spokesperson also confirmed the 44 new cases. Earlier in the week, the spokesperson told ABC News that 23 Americans were among those infected. It's unclear whether the latest cases include any additional U.S. citizens.

Approximately half of all people who were onboard the Diamond Princess are from Japan, while more than 400 passengers are from the United States, according to the cruise line spokesperson.

One of the American passengers on board, Dave Abel, said the rising number of cases is "getting people's moods down."

"One of the passengers in the night was keeping other passengers awake, a lady who was crying for a couple of hours in her cabin," Abel told ABC News in a telephone interview Thursday. "So life isn't as easy as it was last week. It's a bit more challenging."

ABC News' Maggie Rulli, Karson Yiu, Erin Schumaker, Justin Soloman, Anthony Trotter and Sophie Tatum contributed to this report.