Countries with large numbers of cases of a virulent pneumonia should screen passengers at airports for the illness, say experts. The World Health Organisation says that air passengers leaving Hong Kong, Taiwan, Hanoi, Singapore, Toronto and Guangdong province in China should be asked a series of questions to try to spot those carrying the SARS virus. The illness looks likely to have killed more than 50 people worldwide, and air travellers have carried it to more than a dozen different countries in the space of a week.