但是具体什么时间爆发谁都说不好。
耸人听闻？ 这话不是我说的，是亚特兰大EMORY大学流行病专家 Dr. Jay Steinberg 讲的。下面是他的原话：
History indicates that flu pandemics tend to occur once every 20 years or so, So we're due for one, Steinberg said. However, it is not likely to be swine flu, he said.
"I can say with 100 percent confidence that a pandemic of a new flu strain will spread in humans," he said. "What I can't say is when it will occur."
他是在什么情况下讲的这些话呢？说来话长，也是现在的一个新闻事件，我懒得翻译了，下面是英文全文。
Investigators await samples in swine flu outbreak
(CNN) -- U.S. medical experts investigating a novel swine flu outbreak awaited samples Thursday night from Mexico, where a respiratory illness has killed as many as 20 people.
Swine flu is usually diagnosed only in pigs or people in regular contact with them.
Seven cases of a previously undetected strain of swine flu have been confirmed in humans in the United States, the Centers for Disease Control and Prevention said. None of the patients had direct contact with pigs.
Five of the cases were found in California, and two in Texas, near San Antonio, said Dr. Anne Schuchat, the CDC's interim deputy director for science and public health program.
The Mexican samples were to be tested at the centers based in Atlanta, Georgia, spokesman David Daigle told CNN by e-mail. He would not confirm that the samples were related to the respiratory outbreak, but said the CDC "understand Canada has samples, and is testing, and has placed a travel alert for travel to Mexico."
The Public Health Agency of Canada issued a respiratory alert for Mexico on Wednesday, recommending that health providers "actively look for cases" in Canada, particularly in people who've returned from Mexico within two weeks.
The CDC reported Tuesday that two California children in the San Diego area were infected with a virus called swine influenza A H1N1, whose combination of genes had not been seen before in flu viruses in humans or pigs.
CDC confirms 7 cases of swine flu in humans
CDC: Swine flu seen in 2 California children
The seven patients range from age 9 to 54, Schuchat said. They include two 16-year-olds at a Texas school, and a father and daughter in California.
"The good news is that all seven of these patients have recovered," Schuchat said.
The first two cases were picked up through an influenza monitoring program, with stations in San Diego and El Paso, Texas. The program monitors strains and tries to detect new ones before they spread, the CDC said. Other cases emerged through routine and expanded surveillance.
The human influenza vaccine's ability to protect against the new swine flu strain is unknown, and studies are ongoing, Schuchat said.
There is no danger of contracting the virus from eating pork products, she said.
The new virus has genes from North American swine and avian influenza; human influenza; and swine influenza normally found in Asia and Europe, said Nancy Cox, chief of the CDC's Influenza Division.
Swine flu is caused by type A influenza, according to the CDC. It does not normally infect humans, but cases have occurred among people, especially those with exposure to pigs.
There also have been cases of one person spreading swine flu to other people, the CDC said.
In 1988, in an apparent swine flu infection among pigs in Wisconsin, there also was evidence of a patient transmitting the virus to health workers, the CDC said.
Experts think coughing, sneezing and contaminated surfaces spread the infection among people. From December 2005 to February 2009, 12 human cases of swine flu were documented.
Symptoms include fever, lethargy, lack of appetite, coughing, runny nose, sore throat, nausea, vomiting and diarrhea, the CDC said.
The new strain of swine flu has resisted some antiviral drugs.
The CDC is working with health officials in California and Texas, and expects to find more cases, Schuchat said.
There's no need for alarm, but people at risk -- those who live in or have visited areas where patients live, or have had contact with pigs -- should get tested if they notice symptoms, said Dr. William Short at the division of infectious diseases at Thomas Jefferson University Hospital in Philadelphia, Pennsylvania.
A pandemic is defined as: a new virus to which everybody is susceptible; the ability to readily spread from person to person; and wide geographic spread, said Dr. Jay Steinberg, an infectious disease specialist at Emory University Hospital Midtown in Atlanta. The new strain of swine flu meets only one criteria: novelty.
History indicates that flu pandemics tend to occur once every 20 years or so, So we're due for one, Steinberg said. However, it is not likely to be swine flu, he said.
"I can say with 100 percent confidence that a pandemic of a new flu strain will spread in humans," he said. "What I can't say is when it will occur."
