MEXICO CITY - Millions of children, many wearing surgical masks, returned to scrubbed and disinfected classrooms Monday after a nationwide shutdown to curb the spread of swine flu in Mexico.

China, meanwhile, was ramping up efforts to control the disease after a Chinese man who had been studying at the University of Missouri became the mainland's first confirmed swine flu case.

Health authorities in Beijing scrambled to find and quarantine more than 200 people who accompanied him on a flight to China, transmitting messages by radio, television and telephone text asking the passengers to contact officials.

Six of Mexico's 31 states put off reopening schools for a week amid a rise in suspected flu cases in some regions, and a seventh ordered a one-day delay. Some parents were worried about sending their children back so soon.

"Imagine with this disease. What if she gets it?" said Filomena Pena Carriles, lining up outside the Ignacio L. Vallarta elementary school in Mexico City with her eight-year-old daughter Esmeralda, who wore a mask as she waited for teachers to begin checking each of the 135 students for flu symptoms.

The school suspended gym classes and all ceremonies for at least a week as an added precaution, said Maria Magdalena Ruiz, a teacher.

Officials said any students with sympton sent home. They also washed hands of students with sanitizing gel.

Mexico Health Secretary Jose Angel Cordova announced Monday that weekend tests on backlogged samples caused officials to raise their confirmed death toll from 48.

The United States now has the most confirmed cases - 2,532 in 44 states - according to the U.S. Centers for Disease Control and Prevention. Mexico has confirmed 2,003 cases.

In Mexico, crews worked through the weekend to cleanse school buildings and stock them with sanitary supplies as 25 million children prepared to resume their studies after authorities ordered schools closed in the Mexico City region on April 24 and then the whole country three days later.

The federal Education Department said Sunday that 88.9 per cent of the nation's estimated 250,000 schools had been cleaned and disinfected.

Secretary of Public Education Alonso Lujambio urged parents not to send their children back to school if they were sick and told teachers to be on guard for possible flu cases.

"School life will return to normal as long as the safeguards we have put in place are effective. Help us in this," Lujambio said.

Mexican health officials say swine flu has been confirmed in 1,626 people, of whom 48 have died.

High schools and universities resumed classes last Thursday.

The reopening of kindergartens and primary schools is the latest step in Mexico's efforts to restore a sense of normality after the flu scare. Businesses, restaurants and bars gradually resumed operations over the past week, and except for public servants and restaurant workers, it is less and less common to see people wearing surgical masks.

Meanwhile, the government ratcheted up complaints about China's treatment of Mexican citizens because of the swine flu outbreak

Officials said the country would not participate in a Shanghai trade fair May 19-21 as planned because China had withdrawn Mexico's "guest of honour" status. Thirty Mexican companies had been scheduled to take part.

Mexican officials were already angry over China's quarantining of dozens of Mexican travellers, airline flight cancellations and a ban on its pork products - moves that were part of a wider series of snubs by many nations that has left Mexico feeling unfairly singled out.

China has defended the steps as necessary to keep swine flu out of the world's most populous nation.

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