The UN's top health official has opened a forum in Mexico on combating swine flu by saying that the spread of the virus worldwide is now unstoppable.World Health Organization head Margaret Chan added that the holding of the meeting in Cancun showed confidence in Mexico, which has been hard hit.The WHO says most H1N1 cases are mild, with many people recovering unaided.As the summit opened, the UK alone was projecting more than 100,000 new cases of H1N1 a day by the end of the summer.As the peak of the flu season approaches in South America, some areas have declared a public health emergency.El Salvador reported its first death from swine flu, a day after Paraguay reported its first fatality.'Mild symptoms'"As we see today, with well over 100 countries reporting cases, once a fully fit pandemic virus emerges, its further international spread is unstoppable," Dr Chan said in her opening remarks.The UN's top health official has opened a forum in Mexico on combating swine flu by saying that the spread of the virus worldwide is now unstoppable.Source: BBC