Result0's video: heightened concern over new flue-like virus breakout Swine flu

The World Health Organization expressed "heightened concern" on Friday over more than 800 "influenza-like" cases reported in Mexico, after seven cases of a severe respiratory illness were confirmed in two U.S. border states. WHO spokesman Gregory Hartl told CBC News on Friday that health officials are dealing with three separate events in Mexico, with most of the 828 cases in and around the capital, Mexico City. At least 24 cases have been reported in the central region, while four have been reported in the north. The mystery illness has led to at least 20 deaths in the country. Most of the cases have occurred in healthy young adults, Hartl said. "Because these cases are not happening in the very old or the very young, which is normal with seasonal influenza, this is an unusual event and a cause for heightened concern," Hartl said in an interview from WHO headquarters in Geneva. It is also rare to see such high flu activity so late in the season, he said. "The end of April, especially in a place like Mexico, you would think that we would see quite a steep decline," said Hartl. All classes cancelled in Mexico City A Mexican Health Ministry statement issued on Thursday afternoon said the country "was in the presence of a new influenza virus that constitutes a respiratory epidemic which is controllable, so far." But laboratory tests on the 828 Mexican cases have yet to confirm the patients are suffering from influenza, or what strain it might be, Hartl said. The Mexican government ordered that all classes in Mexico City and the surrounding state be cancelled on Friday, from pre-schools to universities. It also has warned the public to avoid gathering places and major events. On Thursday, Canadian health officials issued a travel advisory warning travellers who have recently returned from Mexico to be on alert for flu-like symptoms that could be connected to the illness. In the U.S., health officials were scrambling this week to deal with a new strain of swine flu, which has been diagnosed in seven people in Texas and California. The states share a border with Mexico not far from a town where two deaths were reported. The U.S. cases are unusual, because it appears none of the patients had contact with pigs, and the virus is one that health officials have never seen before. No cases of this swine flu have been found in Canada. Samples positive for influenza A and B The cause of the illness has not been confirmed. Mexican health officials said samples so far have tested positive for influenza A and B. People infected with the virus initially suffer flu-like symptoms that include: * Fever. * Cough. * Sore throat. * Muscle and joint pain. * Shortness of breath. The illness may elevate to a severe respiratory illness within about five days. In Canada, the travel advisory includes the same advice given to all travellers: Get a flu shot and take precautions such as covering coughs and staying home when sick. But it also adds locations in Mexico where cases of a severe respiratory illness have occurred.