(CNN) -- The United States stepped up preparations for a possible swine flu epidemic, and Canada confirmed its first cases on Sunday as researchers worked to determine how contagious the virus could be.
Homeland Security Secretary Janet Napolitano briefs reporters at the White House Sunday. more photos »
Keiji Fukuda, the assistant director-general of the World Health Organization, called the outbreak "serious" on Sunday. Researchers are still trying to determine how easily the virus is transmitted person to person and it's too early to predict whether there will be a mild or serious pandemic, said Fukuda.
Dr. Alejandro Macias, an epidemiologist and adviser to the federal Ministry of Health, told CNN en Español that the official death toll was at 86. Macias said five more deaths in Mexico City had been reported to federal authorities by local authorities in the city.
Earlier, Mexican President Felipe Calderon said 81 deaths were suspected to be from the outbreak and 374 people remained hospitalized. Another 929 people have been examined and sent home, he said.
"These people have shown up at some medical institution in the country with respiratory symptoms that required to be studied and diagnosed," he said.
Mexico City closed all of its schools and universities until further notice because of the virus, and troops passed out filter masks outside the National Cathedral on Sunday morning. No masses were scheduled at the cathedral, but dozens of worshippers put on masks and went inside the church to pray on their own.
Public Health Emergency According to the
At a White House news conference Sunday, Homeland Security Secretary Janet Napolitano said the emergency declaration is standard procedure -- citing that one was declared for the inauguration and for recent flooding. According to the World Health Organization , a public health emergency is an occurence or imminent threat of illness or health conditions caused by bioterrorism, epidemic or pandemic disease, or highly fatal infectious agents or toxins that pose serious risk to a significant number of people.At a White House news conference Sunday, Homeland Security Secretary Janet Napolitano said the emergency declaration is standard procedure -- citing that one was declared for the inauguration and for recent flooding.
Mexican Finance Minister Augustin Carstens said Sunday that the World Bank was lending Mexico $205 million to deal with the outbreak. "We are getting an immediate loan of $25 million for the requisition of medicines, medical equipment and epidemiological equipment and in addition, $180 million to build up strategic operational and institutional capacities to deal with this issue," he said.
Russia announced it is banning meat imports from Mexico and the southern United States due to the outbreak of swine flu, the Interfax news agency reported. Passengers arriving in Russia from Mexico and the United States also will be screened for swine flu, the news agency reported, by having their temperatures taken upon arrival.
Canada confirmed six cases of mild illnesses on Sunday, and the United States reported 20. Meanwhile, Spain, Israel and New Zealand were investigating possible but unconfirmed cases.
In Washington, the head of the Centers for Disease Control said 20 cases had been confirmed in five U.S. states by noon Sunday. The largest number of cases was in New York, where the CDC confirmed cases in eight students at a preparatory school in that city, Mayor Michael Bloomberg said Sunday.
Another seven cases have been confirmed in California, two each in Kansas and Texas and one in Ohio, said Dr. Richard Besser, the CDC's acting director. Only one person has had to be hospitalized, but Besser said authorities are likely to see "a broader spectrum of disease" in the days ahead.
"Given the reports out of Mexico, I would expect that over time we're going to see more severe disease in this country," he said.
Canada's chief public health officer, Dr. David Butler-Jones said the symptoms seen there -- headaches, fevers, coughs and muscle aches -- were mild by the standards of serious flu cases. But he added, "It's still pretty miserable."
The U.S. government declared a public health emergency -- a step Homeland Security Secretary Janet Napolitano said "sounds more severe than really it is."
"This is standard operating procedure and allows us to free up federal state and local agencies and their resources for prevention and mitigation," she said.
The outbreak "is of great concern to the White House," said White House spokesman Robert Gibbs, but, he added, "It's certainly not a time to panic."
"If you're sick, stay home, get treatment, go see a doctor," Gibbs told reporters. "The government is taking all the steps it needs to and must do to take the precautions to deal with whatever size and scope we may be facing," he said. Watch how public health officials grade phases of pandemic alerts »
Meanwhile, the U.S. military issued a worldwide caution, telling its medical personnel to be on the lookout for troops with signs of swine flu and reiterated the need for public health precautions.
The WHO ordered countries worldwide to look out for "unusual" outbreaks of flu following an emergency meeting Saturday. WHO official Gregory Hartl said the strain of the virus seen in Mexico is worrisome because it has mutated from older strains. iReport.com: Do you think we should be worried about swine flu?
"Any time that there is a virus which changes ... it means perhaps the immunities the human body has built up to dealing with influenza might not be adjusted well enough to dealing with this new virus," he said.
A spokeswoman for the Air Transport Association, which represents the U.S. airline industry, said the group is taking the matter seriously.
Airport employees and flight crews are on the lookout for any passengers who show signs of illness, and procedures are in place for determining whether ill passengers may fly, Andrus said.
At Los Angeles International Airport, custodians have been instructed to pay additional attention to sanitizing door knobs, handrails and faucets in airport restrooms, according to a statement from Los Angeles World Airports.
"In addition, public education signs with general tips on preventing the spread of illnesses -- that are posted throughout the airport during regular flu season -- are being re-posted," the statement said.
The H1N1 strain of swine flu is usually associated with pigs. When the flu spreads person to person, instead of from animals to humans, it can continue to mutate, making it a tougher strain that is harder to treat or fight off. Symptoms of swine flu include fever, lethargy, lack of appetite, coughing, runny nose, sore throat, nausea, vomiting and diarrhea, the CDC said. Learn more about swine flu and how to treat it »
In New Zealand, officials said 22 students and three teachers, who returned from a three-week language trip to Mexico, may have been infected with the swine flu virus. The group remains quarantined at home, and Health Minister Tony Ryall said 10 students tested positive for influenza A -- the general category of strains that includes the H1N1 swine flu.
In Spain, six people, all of whom had recently returned from Mexico, were being isolated in hospitals, the country's health ministry reported. And in Israel, doctors are running tests on a man who recently returned from Mexico with light flu symptoms.
In London, a hospital spokesman said a British Airways crew member developed flu-like symptoms during a flight from Mexico City and was tested for swine flu, but the results came back negative. The flight attendant is back at work, British Airways told CNN. Watch CBC report on Canadian microbiologists' concerns »
Concerns over the virus have prompted Canada to issue a travel health notice, saying the public health agency was "tracking clusters of severe respiratory illness with deaths in Mexico." But Mexico's Tourist Board said Saturday there are no restrictions on travel to the country. Watch efforts in Mexico to prevent spread of the virus »
Neither Britain nor the United States have issued any travel warnings or quarantines. But South Korea said it will test airline passengers arriving from the United States, and Japan will convene a Cabinet meeting Monday to come up with measures to block the entry of the virus into the country.
Katherine Andrus, an attorney for the U.S. Air Transport Association, told CNN that the airline trade association was in regular contact with the CDC.
Andrus said airlines are following their own procedures to watch for ill passengers and crews have standard procedures for dealing with ill passengers. Any onboard communicable disease incidents must be reported to the CDC, she said.
"This is a time for appropriate precautions but not panic," Andrus said.
CNN's Saeed Ahmed, Raja Razek, Phillip Warrington, Jeanne Meserve, Paul Vercammen and Ted Rowlands contributed to this report.
All About Mexico • Influenza • Centers for Disease Control and Prevention
3D Model of an influenza virus Officials in Mexico are asking citizens to take actions in order to minimize the spread of the swine flu outbreak. Citizens are urged to stay away from large crowds, avoid kissing people and stay at least 6 feet (1.8 meters) away from one another. Additionally, all schools and universities in Mexico City have been closed indefinitely. In addition, at least twenty people in the United States have been infected with the disease, causing the government to issue a "national public health emergency."

On Monday, Mexican officials reported that at least 100 deaths in their country were "likely linked" to the swine flu. Dr. Jose A. Cordova Villalobos, the health secretary of Mexico, said that at least 20 of the deaths have been confirmed as swine flu related deaths while the World Health Organization (WHO) says that 71 people have died from complications caused by the disease. Meanwhile, over 1,300 people in Mexico have been hospitalized because of flu-like symptoms since April 13.

In New Zealand, 26 students and teachers might have been infected by the flu during their trip to Mexico. Dr. Julia Peters, the clinical director of Auckland Regional Public Health Service, said that at least 22 have shown flu-like symptoms. All of the students and teachers are being quarantined pending test results. Similar health scares occurred in Israel. France, Spain and the United Kingdom, where people with flu-like symptoms have been tested for the swine flu. In the UK, test results came back negative for the deadly strain, while results from Israel, France and Spain are still pending.

In the United States, there have been twenty confirmed cases of swine-flu in the states of Kansas, Texas and California. Today, New York Mayor Michael Bloomberg reported that at least 8 students from a New York preparatory school have contracted the mutated flu strain. The White House also said today that there was at least one confirmed case of the disease in Ohio, prompting the federal government to declare a "public health emergency." 

Robert Gibbs, a White House spokesman, said that the swine flu outbreak "is of great concern to the White House," and that President Obama is now receiving briefings on the issue on a regular basis. Gibbs added, "I would tell people it's certainly not a time to panic ... The government is taking all the steps it needs to and must do to take the precautions to deal with whatever size and scope we may be facing."

The WHO is taking the outbreak very seriously, calling it a "public health emergency of international concern" that has a "pandemic potential." The WHO's emergency council met on Saturday for the first time since its creation. If the committee decides that the swine flu outbreak is an international public health emergency, WHO could recommend travel warnings and restrictions and possible border closures.

The Center for Disease Control says that swine flu symptoms include a fever above 100º Fahrenheit, diarrhea, nausea, vomiting, coughing, sore throat, lack of appetite, runny nose, breathing problems and fatigue. However, not all symptoms are present in each case of swine flu.