Dr. David Acheson of the Center for Food Safety and Applied Nutrition, part of the FDA, said consumers are advised not to eat fresh bagged spinach until further notice, and anyone who has become sick after eating it should consult a doctor.

The brand of spinach, the grower or distributor, and its point of origin remain unknown. The first case came to light on Aug. 23, and the latest was reported on Sept. 3. Dr. Acheson said the outbreak is "ongoing," and suggested that more cases may come to light.

E. coli (Escherichia coli) causes diarrhea, often with blood in the stools. It can lead to hemolytic uremic syndrome, a type of kidney failure that can be fatal, especially in very young and elderly people. Eight persons affected by the current outbreak have developed this condition. For most adults, the illness runs its course in about a week, and recovery is complete.

In Wisconsin, at least 20 people remain ill. One person has been sickened in Connecticut, three in Idaho, four in Indiana, three in Michigan, two in New Mexico, five in Oregon and 11 in Utah. Most of the victims are women.

E. coli bacteria infect approximately 73,000 people a year in the US, causing an average of 61 deaths annually, according to the Centers for Disease Control and Prevention.

They normally reside in animals' intestines and enter the human food chain through fecal contamination. Health officials stress the importance of thoroughly washing all raw vegetables. Other foods that may contain E. coli include raw milk, unpasteurized juices, water and undercooked or raw meat -- particularly ground beef, says the CDC.

Tips for Avoiding E. Coli Infection

The CDC offers the following advice for preventing illness caused by E. coli contamination:

1. Cook all ground beef and hamburger thoroughly. Ground beef should be cooked until a thermometer inserted into several parts of the patty, including the thickest part, reads at least 160 degrees F. Don't eat ground beef patties that are still pink in the middle.
2. If you are served an undercooked hamburger or other ground beef product in a restaurant, send it back for further cooking. You may want to ask for a new bun and a clean plate, too.
3. Keep raw meat separate from ready-to-eat foods. Wash hands, counters, and utensils with hot soapy water after they touch raw meat. Never place cooked hamburgers or ground beef on the unwashed plate that held raw patties. Wash meat thermometers in between tests of patties that require further cooking.
4. Drink only pasteurized milk, juice, or cider. Juice concentrates are also heated sufficiently to kill pathogens.
5. Wash fruits and vegetables thoroughly, especially those that will not be cooked. Children under 5 years of age, immunocompromised persons, and the elderly should avoid eating alfalfa sprouts.
6. Drink municipal water that has been treated with chlorine or other effective disinfectants.
7. Avoid swallowing lake or pool water while swimming.
8. Make sure that persons with diarrhea, especially children, wash their hands carefully with soap after bowel movements to reduce the risk of spreading infection, and that persons wash hands after changing soiled diapers. Anyone with a diarrheal illness should avoid swimming in public pools or lakes, sharing baths with others, and preparing food for others.