The number of confirmed cases of swine flu jumped to 1,025 on Monday, comprising 20 countries, the World Health Organization said.

The death toll climbed as well as Mexico’s health minister announced that a 26th person in the country was confirmed to have died from the H1N1 virus, also called swine flu.

There has been one confirmed death outside Mexico, a Mexican toddler who was in the United States visiting relatives.

The WHO said there were no immediate plans to raise its alert to the highest level, Phase 6. That designation would mean “that we are seeing continued spread of the virus to countries outside of one region,” WHO Assistant Director-General Keiji Fukuda said at a news conference.

“If you are seeing community outbreaks occur in multiple regions of the world, it really tells us if the virus has established itself and that we can expect to see disease in most countries in the world.”

In the United States, the Centers for Disease Control and Prevention reported 286 confirmed cases across 36 states, 60 more cases than the day before.

The numbers are expected to increase. Dr. Anne Schuchat, the CDC’s interim deputy director for public health, said Sunday, “We believe we’re just on the upswing here.”

But in Mexico, where the first cases were reported, illnesses may have peaked for now.

The country announced Monday that it was lowering its health alert from the highest level, red, to orange, or “elevated.”

“The measures we have taken, and above all the public’s reaction, have led to an improvement,” Mexico City Mayor Marcelo Ebrard said.

“But I insist that the virus is still present, that we need to remain on alert and the resumption of activities will be little by little, not all at once.”

Mexico City authorities are considering lifting a shutdown of public venues by Wednesday.

Schuchat said she was “heartened by the Mexican authorities’ reports” but added that because the cases began later in the United States, the peak is likely to be later as well.

U.S. residents gripped by concerns about the swine flu also had a hopeful sign Monday. The St. Francis Preparatory School in Queens, New York — which had the first confirmed U.S. cases of swine flu — reopened Monday.

More than 100 St. Francis students had come down with flu symptoms two weeks ago. Some were tested and found to have the H1N1 virus.

New York City Mayor Michael Bloomberg was on hand to welcome them back to a school that had undergone an intense scrub-down.

“The school has been completely sanitized,” St. Francis Principal Leonard Conway said in a letter to students and their parents.

Some students said they had no fears about returning. But one said, “I’m a little nervous.”

“We’re glad to see each other again,” one boy added.

But while they were reuniting, new cases of swine flu were leaving soldiers isolated in California.

A spokeswoman for the U.S. Marine Base at Twentynine Palms, north of Palm Springs, California, said two new cases of the flu were confirmed by the CDC. The two Marines show no symptoms but are being kept in isolation, spokeswoman Jennie Haskamp said. Previously, one other case was confirmed at the base.

The U.S. Defense Department also reported that a crew member stationed aboard the USS Dubuque in San Diego, California, was confirmed to have swine flu and is currently ashore. The department said there were 13 other “probable” cases among Dubuque personnel.

And California officials were looking into a suspected case at Centinela State Prison in Imperial County. Authorities suspended visitation and other “non-essential activities” at the prison pending confirmation.

Even as health officials worldwide worked to battle the outbreak, intense efforts were under way to develop a vaccine — with lessons from history in mind.

“In 1918, the Spanish flu showed a surge in the spring and then disappeared in the summer months, only to return in the autumn of 1918 with a vengeance,” WHO spokesman Gregory Hartl said Sunday. “And we know that that eventually killed 40 million to 50 million people.”

Health officials are not making such dire predictions in this case. And they can’t know for certain whether the swine flu will make a big return later in the year.

Still, they’re taking no chances.

“This is no time for complacency,” U.S. Secretary of Health Kathleen Sebelius said Sunday. “We want to stay out ahead of this.”

In that effort, health officials have a tool unlike anything they’ve had before.

“This is the best surveillance we’ve ever had,” Fukuda said Monday. “You know, we’re really monitoring and able to see a situation unfold in a way we have never been able to do in history before.”

In Hong Kong, about 200 hotel guests and 100 staff members at the Metropark Hotel remain under quarantine until Friday after health officials determined that a guest there had contracted the H1N1 virus.

“We go down to the lobby for food and then back to the room to eat your food,” said Leslie Carr, a British man who is one of the 300 stuck at the hotel. “Not many people are downstairs hanging around to talk or discuss anything.”

China has denied discriminating against Mexicans, saying it is exercising proper precaution to prevent the spread of the virus.

Hong Kong, in particular, is extra careful after a SARS outbreak in 2003 killed almost 300 people.

“In view of the lack of data … we have to be very cautious,” said Yuen Kwok-Yung of Hong Kong University. “I believe that as time goes by, we can change our strategy.”