Q: Ever since I read the stories about those children who got so sick from eating hamburgers, I've been afraid to serve any meat to my children that isn't well done. But they complain it's too dry. How do you know how much to cook meat? A: To answer your question, we need to explain a bit about the illness you describe. It was caused by the bacteria E. coli, which commonly live in cows' intestines. If eaten by humans, especially children, this bacteria can cause severe diarrheal illness that can proceed to shock and even death. During the slaughtering process, these intestinal bacteria are sometimes transferred to the cow's flesh via the knives the workers use. This doesn't cause a problem for cuts of meat that have distinct surfaces, such as steak or roasts because the E. coli (which are found only on the surface) are killed during the cooking process. However, if contaminated meat is ground up to make hamburger, then some of the surface bacteria get trapped inside the meat. Unless the ground meat (hamburgers, meatloaf or other dish) is thoroughly cooked, some of these interior bacteria may remain alive and cause illness when eaten. Fast food restaurants typically adjust the temperatures of their grills to assure the meat is thoroughly cooked. You can safely serve a roast or a steak to your family, even if cooked rare. However, please cook your family's hamburgers well. Dr. Wilson is director of general pediatrics at the Johns Hopkins Children's Center; Dr. Joffe is director of adolescent medicine.