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The virus sweeps the globe, with cases in at least 47 countries.
The fight to contain the coronavirus entered a new and potentially alarming phase on Thursday as public health officials in the United States and Germany grappled with patients who exhibited no known connection to others with the illness.
That raised the possibility that the virus could have begun to spread locally by an as yet unknown means, or that infected people had spread the disease to others sequentially, making it virtually impossible for the authorities to find and isolate the origin.
Either way, the two cases, thousands of miles apart, underscored how quickly the virus was making its way around the globe after first emerging in China late last year, and how difficult it was proving to contain.
As the number of cases in Japan has steadily risen, the government took the extreme step of closing all schools through March in an effort to combat the outbreak.
President Trump announced that Vice President Mike Pence would lead the American effort to combat the virus, while maps tracking new cases continued to light up in countries around the globe.
During the news conference, the Trump administration continued to send mixed messages about the virus, with public health officials warning of potentially “major disruptions,” while President Trump blamed Democrats and cable news channels for overstating the threat.
Financial markets, whose performance Mr. Trump has used as a benchmark for his presidency, continued their week long declines in Asia and Europe, which often prefigure results in the United States.
In Europe, Denmark, Estonia, Norway and Romania all reported their first cases, while several other countries registered new infections that illustrated the diverse ways the pathogen could cross borders.
Two new cases in Britain, for instance, were linked to Italy and to Tenerife in the Canary Islands of Spain.
While the spread of the virus from northern Italy has been taking place for some time, the spread from Tenerife — where a hotel visited by an Italian doctor who tested positive for the virus remains locked down — would be a first.
In the Middle East, concerns were building about the extent and severity of the outbreak in Iran.
Tehran was characteristically parsimonious with information, and what it did broadcast seemed sketchy and unreliable. The government said on Thursday that 245 people had been infected and that 26 had died. But given a mortality rate that experts have put at around 2 percent, the death toll would suggest that at least 1,100 people had contracted the virus.
Perhaps a better indication of the government’s concern was the decision to cancel Friday Prayers, a cornerstone ritual of the Islamic Republic.
Officials in Kuwait reported 43 new cases on Thursday, all tied to Iran, while Saudi Arabia said that it was suspending all pilgrimages to the holy cities of Mecca and Medina.
Conditions continued to ease in China, however, where the authorities were lifting citywide lockdowns that had ensnared more than 700 million people. In South Korea, by contrast, a major outbreak tied to a megachurch in South Korea ballooned on Thursday to 1,766 documented infections, an increase of 505 from the previous day. Plans were underway to test all 200,000 members of an obscure religious group among whom the outbreak started.
Japan moves to close all of its schools to contain the virus.
Prime Minister Shinzo Abe on Thursday asked all of Japan’s schools to close for a month to help contain the spread of the coronavirus. The country is the second, after China, to shutter schools nationwide over the epidemic.
Speaking before a coronavirus task force meeting on Thursday, Mr. Abe said he was “putting a priority on children’s health and safety” and trying to pre-empt a widespread outbreak that could result “from gatherings of many children and teachers for a long time on a daily basis.”
The number of coronavirus cases has steadily risen in Japan, reaching 186, including four deaths. There have also been more than 700 cases and four deaths from a cruise ship docked in Yokohama, Japan.
Mr. Abe said schools should remain closed through spring break. The Japanese school year ends in March, and the new year usually starts at the beginning of April.
He specifically requested that all elementary, middle and high schools close. He did not mention universities or day-care centers.
The move toward a countrywide shutdown follows a decision on Wednesday by the Education Board of Hokkaido, Japan’s northernmost island, to close more than 1,600 schools in the prefecture until at least March 4. Hokkaido has had 54 confirmed cases and two deaths from the virus.
Hours before Mr. Abe spoke, the mayor of Osaka said he had requested that schools in the city, Japan’s third largest, be closed until March 13.
South Korea and U.S. call off joint military exercises.
The fast-growing coronavirus outbreak touched South Korea’s military alliance with the United States on Thursday, as the two countries announced that they would postpone their joint spring military exercise.
The decision came as South Korea reported 505 new cases of the coronavirus on Thursday, bringing the total number to 1,766, the largest outbreak outside of China. Most of the patients were from Daegu, a city in southeastern South Korea, and in nearby towns.
On Wednesday, the United States military reported the first case of a soldier being infected. The soldier was stationed at a base near Daegu.
Both South Korea and the United States said their annual spring combined training, originally scheduled to take place next month, would be postponed “until further notice.”
South Korea has placed itself on the highest possible alert to deal with the outbreak, suspending nonessential military training and placing more than 9,500 troops under quarantine. It has also barred most of its enlisted soldiers from taking leave.
German authorities scramble to find all those who came into contact with infected man.
Health officials in Germany reacted aggressively on Thursday after a man with no known connection to anyone infected with the coronavirus tested positive for the illness.
In addition to closing schools in the community where he lived, they reached out to hundreds of people who took part in a carnival celebration over the weekend where the man was also present, urging them to stay home for 14 days.
Karl-Josef Laumann, the health minister for the state of North Rhine-Westphalia, where the man lives, said that the authorities were still trying to figure out how the man had contracted the virus.
He remains critically ill and cannot provide information about his recent travels, including the period of time when he was infected and contagious but not showing symptoms.
Still, German officials said they would resist taking measures like those seen in China and, to a lesser extent, in Italy, where entire towns and cities have been locked down.
They cautioned against panic, pointing to success in preventing the spread of the virus last month through simply encouraging people to stay home.
After a man from China infected several employees of an auto producer in Bavaria in January, about 400 people who could have been at risk of spreading the virus were identified and placed in isolation in their homes.
That effectively stopped the spread of the virus, and there are no known cases of infection at this time, said Dr. Lothar H. Wieler, president of the Robert Koch Institute, the German government’s disease control and prevention agency.
Germany is in a much better position to limit the spread of the virus than China was in December, Dr. Wieler said, having the benefit of learning from the experience of the Chinese and others in coping with the infection.
“They did not know what the virus even was,” Dr. Wieler noted. “The situations cannot be compared.”
Australian prime minister warns of a “global pandemic.”
Prime Minister Scott Morrison of Australia, sharply criticized for his sluggish response to the wildfires in recent months, said Thursday that his government would enact an emergency response plan for a pandemic the global health authorities have yet to declare.
“We believe the risk of a global pandemic is very much upon us,” he said. “And as a result, as a government we need to take the steps necessary to prepare for such a pandemic.”
That will include, among other things, extending a ban through March 7 on foreigners who have been to mainland China in the past 14 days. There have been 22 confirmed cases of the virus in Australia, with no deaths.
Mr. Morrison said that Australians should continue to attend schools and mass gatherings, play outdoors and eat in restaurants.
“You can do all of these things because Australia has acted quickly, Australia has gotten ahead of it at this point of time,” he said. “But to stay ahead of it, we need to now elevate our response to this next phase.”
Markets in Europe and Asia slump as spread worsens.
Stocks fell in Europe and Asia on Thursday amid further signs of the coronavirus’s spread around the world and after the United States tried to reassure the public that it was ready to deal with the problem.
European markets were trading about 2 percent lower after the Nikkei in Japan closed down 2.1 percent. Futures markets predicted Wall Street would open lower too, continuing a weeklong slump.
Oil prices also fell, while the price of gold rose, signaling continued nervousness among global investors.
Shares in China bucked the general trend, with Shanghai rising 0.1 percent. Regulators and government-controlled investors often step in to help the country’s stock market in troubled times.
The outbreak has taken a toll on multinational companies. On Thursday, Anheuser-Busch InBev joined the chorus, as the brewer forecast a steep drop in quarterly profit. Marriott, the hotel company, said the virus would weigh on its fee revenue this year.
Companies have scaled back their travel. The French cosmetics giant L’Oréal on Thursday suspended all business travel for its 86,000 employees until the end of March. Nestlé, the giant Swiss-based food company, said it would suspend all international business trips for its 290,000 workers until mid-March.
Clinical trials are expanded for possible antiviral treatment.
The drug maker Gilead Sciences is expanding its clinical trials of the antiviral drug remdesivir as a possible coronavirus treatment into several countries, mainly in Asia.
Two new clinical trials starting in March will involve about 1,000 patients who are severely or moderately ill from the virus, to try to determine which patients would be helped most, Gilead said.
The drug is experimental and has not been approved yet to treat any illness. It is already being tested in Wuhan, China, the center of the epidemic, and on patients who are being treated in Nebraska.
“We are looking for ways we can help the world prepare as well as possible for what appears to be a pandemic at this point,” Dr. Diana Brainard, Gilead’s senior vice president for H.I.V. and emerging viruses, said in an interview.
In the last month, Gilead’s stock has risen 17 percent, to $74.70 at the close of markets Wednesday, from $68.80 in late January.
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U.S. reports its first potential case of community transmission.
A person in California who was not exposed to anyone known to be infected with the coronavirus, and who had not traveled to countries where it is circulating, has tested positive for the infection, the Centers for Disease Control and Prevention said on Wednesday night. It may be the first instance of community transmission in the United States.
“The case was detected through the U.S. public health system and picked up by astute clinicians,” a C.D.C. statement said.
It brought the number of cases in the United States to 60, including the 45 cases among Americans repatriated from Wuhan, China — the epicenter of the outbreak — and the Diamond Princess cruise ship, which was overwhelmed by the virus after it docked in Japan.
The new case, in which the source of infection is unknown, is cause for concern, experts said.
“That would suggest there are other undetected cases out there, and we have already started some low-grade transmission,” said Dr. William Schaffner, an infectious disease specialist at Vanderbilt University.
Some discharged patients later test positive, leading to concerns over Chinese tests’ accuracy.
Fourteen percent of patients discharged in China’s populous Guangdong Province later tested positive for the coronavirus during follow-up examinations, according to the provincial authorities. The finding has led some experts to question the accuracy of the tests that have been used to diagnose patients.
It is unclear if these patients are contagious, said Song Tie, a Guangdong health official, during a news conference. But he said that in the city of Guangzhou, for instance, 13 patients had tested positive again after being discharged, but none of their 104 close contacts showed signs of infection.
Several other regions, including Hainan Province in the south and the city of Chengdu in southwestern China, have said they found patients who tested positive even after being cleared.
Under China’s latest national treatment plan, patients must test negative twice for the virus and have a chest scan before they can be discharged from the hospital. Several medical experts have said that patients who have already been infected with the virus cannot be infected again, as they will have developed immunity.
Chinese official says some lockdown measures went too far.
Some of the lockdown tactics used to stop the spread of the virus in China went too far, a top Chinese security official said on Wednesday.
Du Hangwei, the vice minister of public security, said at a news conference that some members of China’s security forces had practiced “excessive enforcement, simplistic enforcement, and crude enforcement” of quarantines and other containment measures.
It was a rare admission by a Chinese official of excessive force in response to the outbreak.
China has implemented residential lockdowns of varying strictness on at least 760 million people, or more than half the country’s population, according to a New York Times analysis of government announcements in provinces and major cities.
Some episodes of seemingly overzealous enforcement have caused outrage. Videos of local officials in Henan tying up pedestrians who were not wearing face masks were shared widely on social media. In Chongqing, officials paraded four residents through the streets, shaming them for gathering to play mahjong at home.
“The relentless management triggered people’s panic and anxiety,” Mr. Du said.
Saudis halt religious visits to Mecca and Medina.
Saudi Arabia on Wednesday temporarily barred Muslim pilgrims from entering the country to visit the holy cities of Mecca and Medina, as the kingdom tried to slow the spread of the coronavirus, a stark illustration of the fear the epidemic has stirred.
The Saudi royal family derives much of its stature in the Islamic world from its status as guardians of the holy sites, and it very rarely closes them off. The Saudi response contrasts with that of Iran, which has kept its pilgrimage sites open, despite a significant coronavirus outbreak there, and evidence that people who had visited Iran had spread the virus to other countries.
Each year, millions of Muslims make a pilgrimage to Mecca, or Umrah, which can take place at any time of year; the Hajj, the pilgrimage to Mecca that all Muslims are expected to make at least once, takes place in a specific part of the lunar year, which this year falls in midsummer.
Many Muslims also visit the mosque in Medina that was established by the Prophet Muhammad.
The government is “suspending entry into the kingdom for the purpose of Umrah and visiting the Prophet’s Mosque temporarily,” the government-run Saudi Press Agency said.
Reporting and research was contributed by Marc Santora, Russell Goldman, Carlos Tejada, Kevin Granville, Geneva Abdul, Choe Sang-Hun, Zoe Mou, Daniel Victor, Roni Caryn Rabin, Denise Grady, David Yaffe-Bellany, Ed Shanahan, Andrew Keh and Ben Dooley.