International concern is growing over the spread of 'swine flu'. Twenty-five students and teachers in New Zealand, some with flu-like symptoms, have been quarantined and are being tested for swine flu after returning from a trip to Mexico. The virus has already killed more than 80 people in Mexico. It is also spreading across the border into the US, where health officials have reported infections in California, Texas and Kansas. The World Health Organization has declared the swine flu outbreaks a "public health event of international concern".