China confirmed Monday its first case of swine flu on the mainland, underlining the outbreak's global spread, as the United States reported hundreds more cases and warned of further deaths.
Worldwide, the death toll passed 50 after Costa Rican authorities reported its first fatality from the virus, officially known as A(H1N1) influenza, and the United States confirmed a third death.
Fears that infections would gather pace were heightened when China said it had detected its first mainland case in a man who had recently travelled back from the United States.
The 30-year-old was hospitalised with a fever after arriving in the Sichuan provincial capital Chengdu, in southwestern China, from the United States via Tokyo on Saturday afternoon, the health ministry said.
"This is our country's first case of A(H1N1)," its spokesman Mao Qunan said in a statement on its website.
State television said the man, surnamed Bao, was in a stable condition. He flew from Tokyo to Beijing on a Northwest Airlines flight before connecting on a domestic flight to Chengdu, the ministry said.
China, which has come under criticism from abroad for its tough swine flu quarantine measures, was seeking a number of passengers, including foreigners, who took the same Northwest flight as Bao, state media reported.
They included 144 passengers on the flight to Beijing and about 150 on the Beijing-Chengdu flight aboard Sichuan Airlines, state television added, saying some had already been located.
The virus was first reported in Mexico in April but has spread to more than 30 nations since and the global number of infected cases is at least 4,380.
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