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Besides China, three of Mexico’s Latin American neighbors - Argentina, Cuba and Peru - have banned regular flights or travel to and from Mexico. Two dozen countries have imposed embargoes on pork products from Mexico, the United States and Canada.

“If they weaken us economically or in other ways, Mexico will be able to focus much less attention and funds on this problem,” Mr. Calderon said.

Beijing denied it was discriminating against Mexicans, and, in a goodwill gesture, finished sending Mexico $5 million in flu-prevention equipment, ranging from masks and disinfectants to infrared thermal scanners.

As of Monday afternoon, the WHO has confirmed 1,085 cases of swine flu in 21 countries, Dr. Chan told the U.N. General Assembly via videolink from Geneva. The WHO number is significantly lower than most other estimates, as it counts only cases analyzed in its own laboratories.

The virus has killed only Mexicans. One death has been reported in the United States - that of a toddler who was brought to the country from Mexico. The first severe case in Canada was reported Monday.

The organizations say their mounting numbers are mostly the result of confirmations, not new cases.

The A-H1N1 strain - thought to be a stew of swine, avian and human viruses - has not been as lethal as WHO doctors feared. Only 38 percent of the suspected cases in Mexico have turned out to be swine flu, and no deaths from the disease have been reported in Mexico since April 29.

But Health Minister Jose Angel Cordova acknowledged to reporters in Mexico City that about 100 early deaths in which swine flu was suspected may never be confirmed because mucous or tissue samples were not collected.

Dr. Besser was also optimistic Monday, saying that “there are encouraging signs” of a leveling off of the swine-flu threat, though he declined to go as far as his Mexican counterparts in declaring the epidemic under control.

“I’m not ready to say that yet,” Dr. Besser said when asked about indications by Mexican health authorities that the disease has peaked there. “We are by no means out of the woods.”

Pandemic infections have come in waves, “and you don’t know what this virus is going to do.”

Meanwhile on Monday, U.S. health officials said they were reconsidering a recommendation, made last weekend, that schools with suspected cases consider closing for up to two weeks.

“We are looking at our school closure guidance,” Dr. Besser said. “We’re having very active discussions about whether it’s time to revise that.”

Dr. Besser said it may make more sense to “really push hard on the personal responsibility,” encouraging teachers to look out for sick children and insist that parents keep them home.

According to the Department of Education, more than 530 schools in 24 states had given 330,000 students unexpected time off as of Monday.

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