SHANGHAI: Do not store wheat flour at room temperature if you have a child who has asthma.

In the tropics, 1g of plain flour left at room  temperature for a month will have 1,750 dust mites crawling in it.

Leave it for two more weeks and the mite population Ihere will double.

And here's the nub: Even if the flour is cooked at high temperatures, the dead mites can still trigger an attack in an asthmatic, paediatrician Lee Bee Wah has warned.

The adjunct. professor in paediatrics at the National University of Singapore was speaking at the 13th Asian Pacific Congress of Paediatrics here.

The five-day congress ending on Sunday has attracted more than 2,200 doctors and nurses from around the world, with some conling from as far as Costa Rica.

Dr Lee said that at least two children in Singapore have landed in hospital with severe asthma attacks following the consumption of food items made using mite-contaminated flour.

Wheat flour is best kept refrigerated once the package is opened, especially if the food made from it is for people prone to asthmatic attack.

This precaution should be taken with nearly all kinds of wheat flour, including tempura batter and bread flour. Glutinous rice flour, corn flour and tapioca flour are not as likely to breed mites when stored at room temperature.

Dr Lee said some controversial studies done in the temperale climates of Europe and the United State have implied that avoiding dust mites does little to curb asthma attack, but this finding may not be useful in Asian countries.

This is because the much higher populations of mites found in tropical Asian countries make it advisable to maintain the home in ways that would keep them at bay.

The severe attacks of asthma that high concentrations of mites can trigger take two forms: They can either cause the upper respiratory tract to swell, making it difficult for the patient to breathe, or cause a sudden expansion of the blood vessel, which will send one's blood pressure plummeting.

Both forms can kill.

Doctors in the tropics should thus continue recommending that patients practise dust mite avoidance in order to prevent asthma attacks.

In Singapore, between 10 per cent and 12 per cent of school-going children have asthma; among adults, the figure is 5 per cent.

Each year, more than 4,000 people end up in Singapore hospitals as a result of serious asthma attacks; of these, about 500 suffer complications.

Dr Lee said it is not just the mites that cause allergic reactions. Their skin flakes and faecal droppings can also cause harm because they are allergens - that is they can trigger allergic reactions.

This is why asthmatics are advised to avoid upholstered sofas, which trap these allergens.

She added that a battery of other anti-dust mite measures is needed to keep their number down.

Vacuuming carpets removes the allergens but not the mites. It is best not to have carpets at all, and if children have stuffed toys, these should be washed regularly.

Encasing mattresses and pillows in allergen-protective covers helps , but they have to be washed regularly in hot water, or in cool water with detergent and bleach, to get rid of accumulated mite droppings.

Asthma attacks can also be prevented with medication, the cost of which can be covered by Medisave. Since April last year, withdrawals of up to $300 have been allowed from each Medisave account each year or this purpose.