Yet the recent outbreaks of hepatitis A linked to contaminated scallions imported from Mexico, which have killed three people and sickened hundreds, are only the latest examples in a sharp rise of food-borne illness from fruits and vegetables. In 2000, the last year for which information is complete, there were almost as many reported cases of food poisoning from produce as there were from beef, poultry, fish and eggs combined, according to an advocacy group's compilation of government data.
"It's a huge problem and not one easy to solve," said Dr. Glen Morris, chairman of the department of epidemiology and preventive medicine at the University of Maryland School of Medicine and a former Agriculture Department official. "Produce is emerging as an important cause of food-borne illness in this country."
Scientists and some government officials say illnesses have risen sharply because people are eating more fresh produce and want it year-round, leading to an increase in imports from countries with less stringent sanitary standards.
And until recent years, produce was the last place investigators looked for food-borne illness. Less than 2 percent of the produce that crosses the border is inspected for disease-causing bacteria, according to the Food and Drug Administration, which is responsible for the safety of produce.
When the F.D.A. tested 1,003 samples of fresh produce imported from 21 countries in 1999 and 2000, 4.4 percent were found to have harmful bacteria. Of 959 domestic samples, 1.3 percent tested positive. Dr. Bob Brackett, director of food safety and security for the agency, said the results were statistically insignificant because of the study design. But some scientists disagree. "While the study design may not have been optimal," Dr. Morris said, "the differences are striking given the relatively large overall sample size."
Dr. Robert V. Tauxe, an epidemiologist with the federal Centers for Disease Control and Prevention, said, "The American diet has really shifted, and we are eating more that is minimally processed and getting it from a broader variety of different sources." He added: "There has been an increase in the volume of production, so when something goes wrong it goes wrong on a bigger scale. It's a difficult trade-off if you want to have fresh produce in the off-season."
In 2000, there were 3,981 illnesses reported from outbreaks linked to contaminated produce, while 4,025 people were made ill by contaminated beef, poultry, seafood and eggs, according to figures compiled by the Center for Science in the Public Interest, a nutrition advocacy group that frequently criticizes the food industry. The group used statistics from the Centers for Disease Control and state health departments, along with news media reports verified by public health officials, to create the first database linking the outbreaks to specific foods.
Experts say the figures represent only a small percentage of the outbreaks (defined as two or more people who become ill from eating from the same food source). No records are kept for individual cases. The C.D.C. has estimated that each year 5,000 people die and 76 million become ill from food poisoning, largely from unknown causes.
The data from the advocacy group shows that reported outbreaks of produce-related illnesses have risen sharply over the past few years. In 1997 there were 29 such outbreaks; in 2000 there were 76.
Consumers can protect themselves by washing fruits and vegetables thoroughly under running water, peeling produce and removing the outer leaves of leafy vegetables. For people with compromised immune systems, the best advice is to eat only cooked produce.
In 1996 and 1997 large outbreaks of food-borne illness were traced to Guatemalan raspberries; from 2000 through 2002 there were three large outbreaks of salmonella traced to Mexican cantaloupes. In 1999 there was an outbreak of salmonella traced to domestic raw tomatoes.
The United Fresh Fruit and Vegetable Association, a trade group, said that produce had been unfairly singled out.
"Produce has been implicated in a very small percentage of food-borne illness outbreaks," the association said in a position paper, "and most of these were caused by improper handling, not by farm practices."
Dr. Brackett agreed, saying "a significant percentage of produce outbreaks are caused by contamination that occurs at the place of preparation."
Dr. Morris said that some of the outbreaks were due to improper sanitation in processing plants, restaurants and homes, but that many were due to poor sanitation on farms, particularly in foreign countries.
"Infected workers do play a role in some cases, but we've always had infected workers," Dr. Morris said. "And we've put a lot of focus on improving that area so when you see an increasing trend, it's not food handlers; I think it's coming from overseas."
Agriculture Department figures show that in 1997, 20.4 percent of the fresh fruits and vegetables Americans ate were imported. By 2002 the figure had risen to 23.2 percent.
Dr. Mike Doyle, a microbiologist and director of the Center for Safety at the University of Georgia, agrees. "There is a greater potential for contamination to occur in some developing countries where growing standards differ from U.S. standards," Dr. Doyle said. "One of the biggest problems is in the quality of the water used."
Dr. Tauxe of the Centers for Disease Control said: "As far as I know there is not a mandatory requirement that water used to rinse or ice or wash vegetables be potable. There are guidelines recommending this, but in terms of fairness we don't require other countries to meet standards that aren't required in this country."
Critics say part of the problem has been the F.D.A.'s lack of regulatory authority and its understaffing.
The Agriculture Department, which is responsible for meat and poultry safety, has 7,600 inspectors covering 6,500 domestic plants. The F.D.A. has 476 inspectors responsible for 420,000 places where food is held, processed or transported.
Because fruits and vegetables have historically been thought of as safe, they are the last things that investigators look at when there is an outbreak of diseases like hepatitis, giving the contaminated produce a chance to infect more people.
Dr. Brackett said the agency had not paid much attention to produce in the past. "We always assumed food-borne illness came from meat, poultry and seafood," he said.
Dr. Brackett said in an e-mail response to questions that the F.D.A. would have additional authority when the 2002 Bioterrorism Act takes effect on Dec. 12. Facilities that hold, process or transport produce will be required to register with the agency and to keep records showing the source of the produce and where it was shipped. "Both these regulations will facilitate better and more rapid trace-back," he said.