We are planning to fly to the UK from Australia transitting through Singapore with two children under two. Is the risk of contracting Sars on a plane such that we should cancel our trip? Joanna Peterson, Melbourne, Victoria

There is much discussion as to how effective aircraft air-conditioning systems are at removing viruses. The popular view, supported by some research, is that the filter systems are too coarse to remove viruses. Airlines deny this. There is a risk, but it would seem to be small. Don’t forget that it is very likely, if the virus behaves likes its cousin the corona virus, that it will also frequently be transmitted by contaminated door handles, seats, wash basin taps, tables, etc.

Flying anywhere in the Far East must be riskier than flying, for instance, to Italy or France. Flying to that part of Asia must obviously increase the chance of contacting Sars, albeit that chance for any individual traveller must be very low.

Does the virus predominantly affect Asians, or is this irrelevant? Name and address withheld

There is no evidence that Asians are more susceptible, but it is probably not chance that viruses of this sort often start in the Far East. Many people in these countries live in cramped, close quarters, not always with the best sanitation. In urban as well as rural areas they are in close contact with animals. It is probable that there is some shift in the nature of the virus, which has enabled it to jump species. It is not yet 100 per cent certain that the Sars virus is closely allied to one of the group of corona viruses.

Does the wearing of surgical masks make any difference at all in protecting people against Sars? I ask because I cannot get my children to wear them properly and, as they have been off school for weeks now because of the Sars fears, we sometimes have to go to crowded places on the island. Kate Weaver, Hong Kong

Surgical masks do make some difference but they must be clean, and they must be changed frequently. When people have been discussing the spread of Sars, they have tended to extrapolate from what they know about corona viruses. Corona viruses are the second most important cause of colds. In general, a mask is only useful so long as it hasn’t become waterlogged; once very damp from expired breath it may become a reservoir for the virus rather than a protection against it. Furthermore, there is very little experimental evidence to show how efficient masks are at excluding viruses. It is known that they stop surgeons spitting bacteria into patients’ wounds, but their ability to sieve out viruses is less certain.

Another problem with masks is that they need regular adjustment, and this involves the hands being in touch with the face and nose. The important precaution is to wash the hands frequently - and every time before the face or food is touched after the hand has been in contact with possibly contaminated door knobs, bell pushes and other surfaces over which people may have spat, sneezed or dribbled.

It always used to be thought that the way all colds, and therefore the coronas viruses, were spread was through coughing or sneezing. This is still thought to be important, but now it is known that infection is very frequently transferred by nasal secretions on the fingers. A patient with a cough or runny nose contaminates his or her hand, and then this infection is transferred to others via an intermediary surface.

As the corona virus can be spread by coughing and sneezing, an obvious precaution is to avoid those places where people are crowded together like sardines, particularly if conditions are very warm and humid, which would tend to keep the virus alive.

If I had children in Hong Kong I would do my best to see that they didn’t go to crowded places, but I would warn them that constant hand washing is probably more important than the mask.

I have been teaching in China for the past seven months, and at the weekend I visited Beijing. At that stage I was told it was safe to do so. Since my return I have had a bad cough and flu-like symptoms. I have been to the hospital here and they say I am clear but I am still high risk. Is there a chance that I may still have it? I am very frightened, as no one here seems able to tell me. Joanne Cullen, Harbin, China

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