Is it necessary to pass bread and rolls over an open fire to kill germs after people who may have been sick handled them? I do this regularly after bringing them home from the store. How long does it take before viruses or bacteria on a loaf of bread, door handle or keyboard die from exposure to the air or from other causes? - I.N., Jerusalem Prof. Amos Yinnon, head of infectious diseases unit at Shaare Zedek Medical Center in Jerusalem, replies: I always wonder why supermarkets and grocery stores still sell unwrapped bread. I often see people squeeze bread, feel it is not fresh and then put it back into the box. It is not hygienic. Everybody carries a large variety of bacteria, viruses and molds on and inside his body, and these get onto our hands. It is best to buy wrapped bread, even though it is more expensive. Fortunately, a strong immune system helps most of us survive. It is hard to say what danger these pathogens on bread pose to people. I know of no such study. It is certainly more dangerous to people with weak immune systems. But running bread over a flame has no beneficial effect, as to kill pathogens you need to heat at a very high temperature for several minutes, as with pasteurization of milk. Under these conditions, the bread would turn into toast. In hospitals we worry about the spread of nosocomial infections (infections resulting from stays in the hospital). Possible sources include the buttons on TV sets and elevators used by patients, as well as phones and keyboards used by staff members. Some viruses can't live or multiply without nutrients, as in a culture. Others, like HIV, can stay alive for 24 hours on surfaces, but HIV cannot be transmitted by such contact. Sneezes, coughs and direct contact are prime ways of spreading infections there. Patients' medical files placed on the hospital bed can also be a source of infection. The most important thing to avoid infection is to wash your hands frequently, especially after going to the bathroom and before eating. As a mother, I always make sure that my children are wearing hats in cold weather - especially those that cover the ears as well. If covering heads is so important in warding off colds, is there a significant difference in the frequency of colds and flus between the religious and secular communities ? - A.D., Jerusalem Prof. Yinnon answers this as well: The Black Plague killed one third of Europeans - some 25 million people - during the Middle Ages. Infection rates among Jews were relatively low because of their hygienic practices mandated by the Torah and Talmud. As a result, non-Jews carried out pogroms against the Jews, claiming the Jews spread the plague. What helped save many Jews from infection are the laws requiring washing of hands after the toilet, getting up in the morning and before eating. In addition, Jews of this era bathed in the mikve (ritual bath), especially before Shabbat and holidays. Today, there is no doubt that handwashing, especially the vigorous use of soap and warm water before ritual pouring of water on the hands, helps protect religious Jews from infection. But it's impossible to say without a reliable scientific study about the influence of hats. There are so many factors. In any case, handwashing is strongly recommended for reducing infection in all the seasons. My 16-year-old son is moderately shortsighted and needs glasses for seeing the board in school. He doesn't like wearing glasses. A friend of his has bought special contact lenses worn only at night that "shape" the cornea temporarily and make it unnecessary for him to wear glasses during the day. Do these work? Do they cause any harm to the eye? - D.A., Tel Aviv Prof. Anat Loewenstein, head of the ophthalmology department at Tel Aviv Sourasky Medical Center, answers: This is called orthokeratology. It is very questionable if such lenses improve eyesight. In addition, since the lenses fit very tightly over the eye, they are even more likely to cause eye infections than ordinary contact lenses. I would not recommend them at this point in time. Rx For Readers welcomes queries from readers about medical problems. Experts will answer those we find most interesting. Write Rx For Readers, The Jerusalem Post, POB 81, Jerusalem 91000, fax your question to Judy Siegel-Itzkovich at (02) 538-9527, or e-mail it to email@example.com, giving your initials, age and residence.