Efforts to contain the coronavirus outbreak showed signs of faltering during the weekend, as Washington, D.C., confirmed its first case Saturday, and Italian leaders announced a plan early Sunday to lock down an entire region including Venice and Milan after reporting 1,000 new cases in 24 hours.

The virus’s exact reach remains unknown. Late Saturday, the American Conservative Union announced an individual who attended the Conservative Political Action Conference less than two weeks ago had tested positive. President Trump, Vice President Pence and a number of other top White House officials had appeared at the four-day event in Maryland.

White House press secretary Stephanie Grisham said neither Trump nor Pence was in “close proximity to the attendee,” but ACU chairman Matt Schlapp told The Washington Post on Saturday that he himself interacted with the infected person at the event. The precise chronology could not be learned, but Schlapp did shake Trump’s hand on the stage on the last day of the conference.

“I think we have to be calm and see what occurs here and hope our friend gets better,” Schlapp said.

White House officials appeared to minimize the risk but said they were taking precautions. Trump told reporters at his personal resort in southern Florida that he wasn’t worried.

“I’m not concerned at all,” Trump said as he met with Brazilian President Jair Bolsonaro for dinner. He also indicated his campaign rallies, which draws thousands of supporters to large venues nationwide, will continue, saying: “We’ll hold tremendous rallies.”

The virus has spread to more than 30 U.S. states and 99 countries, according to a Washington Post analysis. At least six U.S. governors have declared states of emergency. There are more than 100,000 infected people in the world and more than 400 confirmed cases in the United States, where there have been at least 19 deaths. This includes the addition Saturday of two in Washington state. Florida officials announced two deaths on Friday night. Officials said they had not known one of the two people was infected until after the death.

Across the United States and the globe, scientists are racing to develop a vaccine and a treatment to contain the novel coronavirus. (The Washington Post)

At a White House news conference Saturday, Health and Human Services Secretary Alex Azar and Food and Drug Administration Commissioner Stephen Hahn were unable to say how many Americans had been tested for the novel coronavirus. The only figures they had were from the Centers for Disease Control and Prevention and public health labs; the two officials said the CDC so far has tested 1,583 people, and the CDC and public health labs combined have performed 5,861 tests so far. By comparison, South Korea has reported testing 10,000 people per day.

“At this time, the risk to most Americans from covid-19 remains low, but that risk can be higher for those who may have exposure to confirmed cases and for those who have traveled to affected areas,” Azar said. “At this time, most Americans don’t need to change their day-to-day lives but should stay informed and practice good hygiene.”

Until this weekend, all of the confirmed U.S. coronavirus deaths had been in Washington state and California, but that changed Saturday when the Florida Health Department confirmed two deaths. Officials said both patients were senior citizens and had traveled internationally. One patient, in Santa Rosa County, had been previously confirmed to have the virus. The other, in Lee County, tested positive only after death, according to Sen. Marco Rubio (R-Fla.).

As of Saturday, more than 270 people were being monitored for symptoms in Florida, and results of some 80 tests were pending.

There were growing signs Saturday that U.S. companies and institutions were bracing themselves for a long and painful disruption of their operations. Amtrak announced it was canceling its nonstop Acela service from Washington to New York until May 26. Stanford University moved all of its classes online for the winter quarter. SalesForce, the largest private employer in San Francisco, instructed its California workforce to consider working remotely for the month of March.

Overseas, a Navy sailor based in Naples was the first U.S. service member in Europe to contract the novel coronavirus, the U.S. military’s European Command said Saturday. U.S. citizens on a Nile River cruise tested positive for the virus and are being held in Egypt. Among them is Matt Swider, an editor at Tech Radar in New York, who said he and at least three other Americans were taken on an Egyptian military aircraft to a hospital. American tourists are quarantined in a hotel in the West Bank.

The virus continued to wreak havoc overseas.

With a dramatic surge in new cases, particularly in its Lombardy region, Italian prime minister Giuseppe Conte announced a dramatic expansion of the country’s no-entry zone to include a broad northern area and other provinces.

The decision, which would apply to 16 million people, is the most serious step taken anywhere outside China to contain the coronavirus outbreak, according to local media.

The measures would at least temporarily transform the nation, locking off much of the northern part of the country, but people would be allowed to exit and enter the territory for emergencies and urgent work matters. The changes would cut off the daily high-speed rail connections between Milan and Rome; bring a halt to tourism in Venice, and essentially bring Italy’s economic heartland to a standstill.

In China, meanwhile, a hotel that was used to quarantine people suspected of having the virus collapsed, trapping about 70 people, according to the People’s Daily, an official government news outlet. Many were later rescued.

White House officials continued Saturday to urge calm as the Trump administration faced escalating criticism for playing down the gravity of the situation and failing to make test kits available sooner.

“This is a dynamic and constantly evolving situation — not just day-by-day but hour-by-hour,” Hahn said. “So I also recognize that this and other factors may have led to confusion around the diagnostic tests.”

Though top U.S. officials could not say how many Americans had been tested for the coronavirus, they said that as of Friday night, 1.1 million tests had been shipped to nonpublic health labs.

Gov. Andrew M. Cuomo (D) of New York, which has a total of 76 confirmed cases, declared a state of emergency and blasted the Trump administration for not testing more aggressively. He accused Trump officials of creating more anxiety by sowing confusion about the country’s testing capacity.

“I think the anxiety and the fear is a bigger problem than the virus,” he said.

One of the biggest logistical problems confronting officials is what to do with the Grand Princess cruise ship, which has at least 20 people on it with coronavirus and is lying off the California coast. Carnival Cruise Line, which runs the company, said it had no clearer indication of where the ship would end up. Company officials said they had been in touch with federal and state leaders as well as the Port of San Francisco, the ship’s original destination. Frustration, however, was mounting over the uncertainty about when the ship would dock and where, as well as the lack of an established testing regimen for passengers and crew members.

“Our guests who expected to disembark today still do not know what to expect next,” Jan Swartz, the group president of Princess Cruises and Carnival Australia, said on a conference call with reporters Saturday. “We understand that discussions are ongoing with the various government authorities, and so we await a decision as to where we will be berthing the ship,” Swartz added in response to a question. She later said: “We need to get the ship into a port as soon as possible.”

In Washington, officials were still trying to determine the potential implications of the CPAC attendee’s diagnosis. White House officials would not say whether any other senior administration officials who attended the event were being tested. In addition to Trump and Pence, a slate of Cabinet officials, including Azar, Energy Secretary Dan Brouillette, Transportation Secretary Elaine Chao, Education Secretary Betsy DeVos and Secretary of State Mike Pompeo, appeared at CPAC.

White House staffers who spoke at CPAC included departing acting White House chief of staff Mick Mulvaney; Larry Kudlow, the director of the National Economic Council; White House counselor Kellyanne Conway, and senior advisers Ivanka Trump and Jared Kushner.

Miriam Berger, Chico Harlan, Hannah Dreier, Hannah Knowles, Meryl Kornfield, Lateshia Beachum and Faiz Siddiqui contributed to this report.