By Elizabeth Landau, CNN 

The H7N9 strain responsible for the bird flu outbreak in China is unlike any that has previously been seen in this type of virus. So far, 110 cases have been reported, including one in Taiwan, and 23 people have died. So far, authorities said, there is no evidence that this virus can pass from person to person. That doesn't mean it can't happen later. "If limited person-to-person transmission is demonstrated in the future, this really will not be surprising", said Keiji Fukuda, the assistant director for health, security and the environment of the World Health Organization (WHO). The virus appears to be transmitted more easily from poultry to humans than H5N1, Fukuda said, referring to the strain responsible for the outbreak between 2004 and 2007, which claimed 332 lives. "This is definitely one of the most lethal influenza viruses that we have seen so far", he said. 

The H7N9 strain was never known to infect people until March. Before then, it was only found in birds. If the virus does start to spread easily between people, it could trigger a pandemic. "This is a serious public health situation and it's possible that a pandemic could start if this virus were to change to spread easily between people", the U.S. Centers for Disease Control and Prevention (CDC) said on its website. It's not clear why this virus strain is infecting humans now, and the source of the infection is unknown. Scientists have analyzed the genes of the H7N9 viruses and found that they show signs indicating they can adapt to grow in mammals. It appears they can bind to mammalian cells and grow at temperatures near mammals' normal body temperatures, which is lower than that of birds, WHO said. 

There is no vaccine available, but WHO said efforts are underway in other countries after Chinese officials said international help would be needed. The CDC is not advising against traveling to China, but travelers who go there should refrain from touching birds and other animals and wash their hands often. There are no tests available at pharmacies or doctors' offices to distinguish this flu quickly from any other flu virus, the CDC said. However, there is a sophisticated test to detect the H7N9 virus in particular, which takes at least four hours. "Anyone with fever, coughing or shortness of breath within 10 days of traveling to China should see a doctor and tell the doctor about the recent travel to China", the CDC said on its website.

(Adapted from <http://edition.cnn.com/2013/04/25/health/bird-flu-facts/index.html?iid=article_sidebar>.)

n the sentence “However, there is a sophisticated test to detect the H7N9 virus in particular, which takes at least four hours” which alternative can replace “However” without changing the meaning?