Already, streets in the capital seemed more lively, with more vehicles and fewer people wearing face masks. Some cafes even reopened ahead of time. President Felipe Calderon said universities and high schools will reopen on Thursday, and younger schoolchildren should report back to school on May 11.
"The school schedule will resume with the guarantee that our educational institutions are in adequate hygienic condition," promised Calderon, who called on parents to join educators in a "collective" cleansing and inspection of schools nationwide.
"This is about going back to normalcy but with everyone taking better care," Calderon said.
Parents and teachers will turn away children who appear sick.
The government is spending $15 million for detergent, bleach and soap to clean buildings, in a country where 12 percent of the nearly 250,000 schools - about 30,000 - lack running water or bathrooms.
Mexico canceled its biggest celebration of the Cinco de Mayo holiday Tuesday, a re-enactment of the May 5, 1862 victory over French forces in the central state of Puebla. Other holiday events also were canceled.
And experts inside Mexico's swine flu crisis center warned that the virus remains active throughout Mexico and could bounce back once millions return to work and school. It also may get worse north of the border.
"The bottom line is that there hasn't been time for the severe illnesses to perhaps show up in the U.S. yet," Marc-Alain Widdowson, a medical epidemiologist from the U.S. Centers for Disease Control and Prevention, told The Associated Press.
Experts in the U.S. also urged caution, even as a New York City school reopened Monday after a spring break trip to Mexico led to as many as 1,000 people being sickened.
"We are by no means out of the woods," said Dr. Richard Besser, acting director of the CDC.
Health Secretary Jose Cordova insisted that swine flu infections are trending downward after 27 deaths at the center of the epidemic. He said those infected appear to pass it on to an average 1.4 other people, near the normal flu rate of around 1.3.
Cordova said soccer stadiums and concert halls could reopen - if fans are kept 2 meters apart.
But other experts said the known cases are almost certainly only a fraction of what's out there, meaning more illnesses could surface once crowds gather again in Mexico.
"It's clear that it's just about everywhere in Mexico. I think now there is considerable person-to-person transmission," Widdowson said. And now that the virus is taking off in the U.S., chances of severe cases could rise as well.
"We've seen in many of the cases in Mexico, there's been sometimes five to seven days of being mildly ill with increasing respiratory distress and then being hospitalized, and then spending five days or a week in hospital, so that's a timeline of two weeks," he said.
As of Monday, Mexico had 802 confirmed cases, and U.S. case grew to at least 300 in 36 states. Globally, the virus has reached more than 1,276 people in 20 countries - still in its early stages, to the World Health Organization.
The WHO was studying whether to raise the pandemic alert to 6, its highest level, which would mean a global outbreak has begun. WHO uses the term pandemic to refer to geographic spread rather than severity. Pandemics aren't necessarily deadly. The past two pandemics - in 1957 and 1968 - were relatively mild.
"We do not know how long we will have until we move to Phase 6," WHO Director-General Margaret Chan said. "We are not there yet. The criteria will be met when we see in another region outside North America, showing very clear evidence of community-level transmission."
The Southern Hemisphere is particularly at risk. While Africa still hasn't reported any swine flu infections and New Zealand is the only country south of the equator with confirmed cases, winter is only weeks away. Experts worry that typical winter flus could combine with swine flu, creating a new strain that is more contagious or dangerous.
Still, the U.N. health agency urged governments to avoid unproven actions to contain the disease, including group quarantines of travelers from Mexico and bans on pork imports.
"Let me make a strong plea to countries to refrain from introducing measures that are economically and socially disruptive, yet have no scientific justification and bring no clear public health benefit," Chan said in a video message to the U.N. General Assembly in New York.
Calderon said other governments have treated his citizens unfairly, and that punishing nations that report outbreaks sets a bad precedent for future flu control efforts. "If they weaken us economically or in other ways, Mexico will be able to focus much less attention and funds on this problem," Calderon said.
Mexico's Economy Secretary, Gerardo Ruiz, said Mexico will bring the issue to the World Trade Organization if other countries don't drop restrictive measures.
Beijing denied that it is discriminating by quarantining Mexicans and any other passengers who came in close contact with them, even those who don't show symptoms.
Among the passengers stuck in Chinese hotels was Briton Mark Moore, who urged China to lift the quarantine.
"The government is trying to show the world they are strong in organizing this," the 37-year-old director of a Singapore-based company said in a phone interview. "I need to be in Singapore now. I have loads of things to do."
A group of 25 Canadian university students and a professor also were quarantined in China over swine flu fears, said University of Montreal spokeswoman Sophie Langlois. The group does not have any symptoms, Langlois said.
China, Argentina and Cuba are among the nations banning regular flights to and from Mexico, marooning passengers at both ends. Mexico and China both sent chartered flights to each other's countries to collect their citizens. Argentina also charted a flight to bring Argentines home.
And in a goodwill measure, China sent Mexico the final batch in a $5 million humanitarian assistance package consisting of masks, gloves, disinfectants, infrared thermal scanners and other items.
The latest figures from Mexico suggest the virus may be less lethal and infectious than originally feared. Only 38 percent of suspected cases have turned out to be swine flu, and no new deaths have been reported since April 29. But Cordova acknowledged that about 100 early deaths in which swine flu was suspected may never be confirmed because mucous or tissue samples were not collected.
Widdowson, of the CDC, said it's too early to say the outbreak is waning in Mexico, but the signs of progress are clear.
"What we have not seen in Mexico City is a huge, runaway epidemic, and I think that's totally clear. The hospital capacity has not been exceeded. So there hasn't been anything like the kind of picture that people might expect from a severe flu," he said. "I think that gives us optimism."
Good hygiene can be a challenge in Mexico's crowded schools - a problem illustrated by 10-year-old Carolina Arteaga, who wandered with a plastic cup in downtown Mexico City Monday, begging money from people outside gleaming office towers. She had no surgical mask and no gloves as she eagerly rubbed a few coins together with grubby fingers.
"I forgot it at home," the fourth-grader said when asked why she didn't have her mask.
Carolina will soon be returning to school and says she knows to wash her hands frequently. But because she needs to collect money to help her mother buy food, such instructions probably won't be carried out.
For facts about influenza, and more information about swine flu, please visit the Health Department and CDC websites. Some specific resources:
From New York City Health Department
Facts about flu
From Centers for Disease Control and Prevention
General information about swine flu
Swine Flu Case Definitions
Swine Flu Infection Control and Patient Care
Preventing the Flu
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