An Update on the 2006 Spinach Outbreak and Produce Safety

Richard H. Linton
Professor of Food Safety
Director of the Center for Food Safety Engineering
Department of Food Science, Purdue University

An Update on the 2006 Spinach Outbreak

Within the past ten years, there has been considerable concern about the safety of fresh produce. Numerous outbreaks have been associated with fresh vegetables (i.e. sprouts, tomatoes, lettuce, cabbage, celery, Cole-slaw, cucumbers, mushrooms, potatoes, radishes, green onions), fruit (i.e. cantaloupe, watermelon, raspberries, strawberries), and fruit juices (i.e. orange juice, apple juice).

As of September 26, 2006, 183 cases of illness have been reported due to spinach contaminated with E. coli O157:H7 including 29 cases involving a type of kidney failure called hemolytic uremic syndrome (HUS), 93 hospitalizations, and one death. These numbers are expected to increase as the full extent of the outbreak unfolds. Spinach implicated in the current outbreak was grown only in Monterey, San Benito, and Santa Clara counties in California. The Food and Drug Administration (FDA), the Centers for Disease Control and Prevention (CDC), and the State of California continue to work together to establish the sources and causes of the contaminated product. Outbreak information is updated regularly by FDA and more information about produce safety is available at: http://www.fda.gov/oc/opacom/hottopics/spinach.html.

Guidance for Industry

These recent outbreaks have promoted several food safety initiatives to better protect public health from pathogens associated with fresh produce. In 1998, the FDA published a document entitled "Guide to Minimize Microbial Food Safety Hazards for Fresh Fruit and Vegetables which can be found at: http://www.cfsan.fda.gov/~dms/prodguid.html. This guidance document addresses microbial food safety hazards and good agricultural and management practices common to the growing, harvesting, washing, sorting, packing, and transporting of most fruits and vegetables sold to consumers in an unprocessed or minimally processed (raw) form. Cornell University then assumed a leadership role in developing a national program on Good Agricultural Practices (http://www.gaps.cornell.edu/). This program has a wealth of information on produce safety, behavioral practices to minimize risk, and produce interventions. A full curriculum is available on the university's website, in English and Spanish, intended for production agriculture, distribution, and produce manufacturing employees.

In 2004, FDA published a document called Produce Safety from Production to Consumption: 2004 Action Plan to Minimize Foodborne Illness Associated with Fresh Produce Consumption (http://www.cfsan.fda.gov/~dms/prodpla2.html). There are four main objectives of the action plan which are to: 1) prevent contamination of fresh produce with pathogens, 2) minimize the public health impact when contamination of fresh produce occurs; 3) improve communication with producers, preparers, and consumers about fresh produce, and 4) facilitate and support research relevant to fresh produce.

Related to leafy vegetables, like spinach and lettuce, there is a special initiative called the lettuce safety initiative (http://www.cfsan.fda.gov/~dms/lettsafe.html). The initiative is intended to a) assess current industry approaches and actions to address the issue of improving lettuce safety, b) alert consumers early and respond rapidly in the event of an outbreak, c) document observations that identify practices that potentially lead to product contamination, and d) consider regulatory action, as appropriate, based on conditions and practices that could lead to, or spread contamination, or when lettuce has been adulterated. While the initiative focuses on lettuce, the safety of other leafy vegetables will also benefit from this program.

Guidance for consumers

The FDA is advising consumers not to purchase or consume fresh spinach if they cannot verify that it was grown in areas other than the California counties of Monterey, San Benito and Santa Clara. The fresh spinach implicated in the current outbreak was grown in these three counties in California only. Spinach from the rest of the U.S. has not been implicated in the current E. coli O157:H7 outbreak. Therefore, the public can be confident that spinach grown in the non-implicated areas can be consumed safely. Processed spinach, including frozen and canned spinach, is also not implicated in this outbreak. Both of these products have been heated to well over 160ºF, which is the temperature required to kill E. coli O157:H7 in spinach. Any other type of leafy greens (lettuce, collard greens, kale) are not implicated in this outbreak.

While cooking is the most effective method for destroying E. coli O157:H7 in foods, FDA is alerting consumers and food handlers not to cook spinach that may be contaminated. Likewise, FDA is also alerting consumers and food handlers not to wash raw spinach that may be contaminated. In both cases, there are just too many opportunities for cross-contamination where the bacteria may be transferred from the contaminated spinach to other foods and food-contact surfaces in the kitchen. The effectiveness of produce washing for reducing microorganisms has been highly debated in recent years. Leafy greens that are packaged into bags are normally subjected to a vigorous wash and then a sanitizing bath during manufacturing and packaging. Additional washing at home or in retail food establishments, while a good idea, may only have a minimal impact for reducing the microbial load to a safe level.

E. coli O157:H7

E. coli O157:H7 belongs to a group of bacteria called enterohemorragic Escherichia coli. Many people are curious about how E. coli O157:H7 was named. The "O" and the '"H" represent cellular and flagellar antigens, respectively, that are associated with the bacterial cell. These antigens are numbered depending on certain characteristics and this information is used to classify or name the bacteria. Escherichia coli is commonly found in the intestinal tract of warm-blooded animals. Approximately 10% of the bacteria found in the human intestine are made up of Escherichia coli. Most Escherichia coli bacteria are harmless and some types actually benefit human health. Fortunately, only a few types of Escherichia coli are harmful including E. coli O157:H7.

E. coli O157:H7 is dangerous because of the disease that it can cause. For healthy people, disease symptoms can range from flu-like symptoms to bloody diarrhea. However, for people who are immuno-compromised , the disease can lead to a disease called hemolytic uremic syndrome which can result in kidney failure and sometimes death. The immuno-compromised individuals who are most vulnerable are infants, children, and the elderly. Another concern of the infection caused by E. coli O157:H7 is that the infective dose may be as low as 10 cells. This is quite different compared to other disease-causing organisms where the infective dose may be in excess of a million cells.

The E. coli O157:H7 organism can be associated with any food that comes in contact with feces from animals or humans . The most likely source of contamination is the meat slaughter facility or milking operations. However, fruits and vegetables may also be contaminated during growing, harvest, and transportation. In recent years, unpastuerized apple cider, raw lettuce, and raw spinach have been implicated as a source of contamination and illnesses.

Since 1995, there have been 19 outbreaks of foodborne illness caused by E. coli O157:H7 for which lettuce or leafy greens were implicated as the outbreak vehicle. Although trace backs to growers were not conducted (or "not conclusive") in all of the outbreak investigations, a majority of the outbreaks traced product back to California growers, many of which were from the Salinas Valley, though not exclusively.

Prevention and control of E. coli O157:H7 needs to be implemented from the farm to processing to consumption. Many prevention techniques are being studied to prevent and/or reduce contamination on the farm including manure treatment, water treatment, and animal feeding operations. After the farm gate, care is being taken to ensure that transportation vehicles and processing equipment are cleaned and sanitized effectively. Informing the consumer is also an important part of prevention. For example, recommendations for handling meat are located on the packages of most raw meat products. This label helps educate consumers on thawing and cooking foods safely, avoiding cross contamination, and the importance of handwashing. There are many methods that can be used to reduce the risk of contamination; however, the best assurance of safety is through heating. Depending on the food product, E. coli O157:H7 is easily destroyed when food is heated to temperatures between 155º and 165ºF. However, this important safeguard is not available for fresh spinach and other ready-to-eat foods that are not usually cooked before they are eaten.