The current epidemic of swine influenza A/H1N1, began in Mexico City in March, and has resulted in 1516 laboratory-confirmed cases, of whom 30 have died (at the time of writing, 6 May 2009). The virus has spread rapidly to 21 countries including Austria, Canada, China, Hong Kong Special Administrative Region, Costa Rica, Colombia, Denmark, El Salvador, France, Germany, Ireland, Israel, Italy, the Netherlands, New Zealand, Portugal, Republic of Korea, Spain, Switzerland and the United Kingdom. To date, all deaths have occurred in either Mexico (n = 29) or the USA (n = 1).1 By the end of April, hundreds of schools had been closed in the USA and Mexico, and the Mexican government had ordered a halt of all non-essential activities of the country for several days.2 3

Deaths have occurred predominantly in young healthy adults,4 in contrast to mortality resulting from infection with most influenza strains which result in increased mortality in those with weak immune systems, including infants and the elderly. This has been observed previously in influenza pandemics and may be attributable …