I am a 79-year-old man with a kidney stone. A stent was implanted at the end of January, and an operation is planned to remove the stone soon. Since the stent was put in to hold the ureter open, I have had no pain or discomfort. If I choose not to have the operation, what would be the consequences? Is it possible to continue live a normal senior's life without surgery? J.B., Eilat Dr. Mordechai Duvdevani, of the urology department at Hadassah University Medical Center in Jerusalem's Ein Kerem, replies: A stent is usually only a temporary means to ease pain and discomfort. It can't be left in the body, as it is a foreign object. It is left in for a maximum of three or four months. Although I have no more details about your medical condition, I would say that if your doctors decided you need surgery to remove the kidney stone, you should go ahead with it. I have always enjoyed taking my family out to picnics in the summer months, but I got nervous last year after several people taking part in a picnic I prepared got sick. What advice do you have to choose appropriate foods for outdoor eating in the heat and avoid food poisoning? E.V., Tel Aviv Marjorie Fitch-Hilgenberg, an associate professor of dietetics at the University of Arkansas, says: The main thing is to keep raw and cooked food cold. Take two or even three extra coolers with you and freeze ice in chunks, which will last much longer than the small cubes in bagged ice. You can do this by putting water in a rectangular cake pan and putting that in the freezer. Put that chunk of ice in a well-sealed plastic bag in the bottom of the cooler, add ice cubes with the food and top it all off with another chunk of ice. It lasts through the hottest weather. It can also serve as a serving tray on the table for potato salad or other sensitive foods. One cooler can carry extra bagged ice, while another can be dedicated to beverages and snacks, such as fruit and vegetables, that can tolerate the constant opening and closing of the cooler. Another cooler can hold raw meat. Prepare fresh-meat hamburger patties at home and freeze them in advance. If you have to keep raw meat with prepared foods, make sure they are well wrapped and are not in contact. Mayonnaise has gotten a bad name unfairly, as it's not the mayonnaise in potato salad that causes problems, but rather bacteria introduced during preparation or bacteria that develop while the salad is sitting out in the heat of the day. Mayonnaise is highly acidic since it's made with vinegar or lemon juice. You need to look at the pH of a food, not just the temperature. Most bacteria are pH-sensitive - that's why a dill pickle lasts a lot longer than a fresh cucumber. Anyone grilling meats or serving other foods needs to wash hands frequently. If there is no running water, bring bottles of water along plus lots of wet-wipes. Washing is key to preventing cross-contamination from raw meat to cooked meat or vegetables; cross-contamination can occur when the cook picks up a bun to toast it on the grill using hands that have handled raw meat. Watermelon can also carry bacteria on its rind, so wash it thoroughly at home and take it in a bag whole to the picnic. Cut it and serve it at the table. I am a 55-year-old man. I take 50 milligram iron (Solgar) because I am somewhat anemic and calcium (600+D) for osteoporosis. Is there a problem taking them together, and how much time must I wait to take the iron before or after consuming milk products? Five pharmacists have told me entirely different things. I.N., Jerusalem Prof. Jeffrey Aronson, a senior expert in the department of clinical pharmacology at Oxford University in the UK, comments: Calcium does seem to reduce the absorption of iron, although not all studies have shown this - which may be the reason for the conflicting information that you have been given. If in doubt, it is best to assume that there is an interaction. When an interaction between two drugs occurs in the gut, altering absorption, one should take the two medicines separately, about two or three hours apart. 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 firstname.lastname@example.org, giving your initials, age and residence.