Also ill are two Australian siblings, aged six and seven, who were travelling to Singapore for a holiday with their family and were picked up by the thermal scanner at the airport.

The other patients are a 12-year-old and 15-year-old returning from Melbourne and the United States respectively. Both are Singaporean boys studying in those countries.

All are in stable condition, the Ministry of Health said yesterday. The six new cases bring the total number of cases here to 27, of whom 15 have been discharged.

The cases here fall within an age range of three to 50, with the largest group in their 20s.

The old are not weaker when it comes to keeping the new flu bug at bay, in contrast to seasonal flu, which is more likely to hit the elderly more severely, said the director of the Health Ministry's communicable diseases division, Dr Lyn James.

Like the seasonal flu, cases here have been relatively mild, but complications could develop in certain groups, such as those who already have underlying illnesses, she said. The profiles mirror those of H1N1 patients in the United States, said Dr James yesterday.

About 70 per cent of those in the US, Canada and Mexico who developed complications severe enough to warrant hospitalisation had pre-existing medical conditions such as a weakened immune system, asthma or heart disease, she said.

'The risk groups for H1N1 are similar to seasonal flu, except for the notable absence of the older age group of 65 and above.'

In Singapore, of the cases before yesterday's six, half are aged below 23 and the other half, above 23. In New York City, the median age is 19. In California, it is 27.5 and in Canada, 17.

Read the full story in Saturday's edition of The Straits Times.

wycin@sph.com.sg