The FDA’s list of the ten riskiest foods in the US

Friday, 01 January, 2010

In the US, ten foods alone have accounted for nearly 40% of all foodborne-illness outbreaks linked to FDA-regulated foods since 1990.

The Center for Science in the Public Interest (CSPI) used data from the Centers for Disease Control and Prevention (CDC) and elsewhere to track more than1500 separate, definable food-borne illness outbreaks that were linked to the foods regulated by the Food and Drug Administration (FDA). The ‘FDA Top Ten’ come from all areas of the food supply: not only high-risk products, like seafood and dairy, but also the must-eat components of a healthy diet, like fruits and vegetables.

The 50,000 illnesses reported, ranging from temporary gastrointestinal distress to long-term disability and death, really only represent the tip of the iceberg as people rarely see a doctor to treat foodborne illness and those who do are often treated without the laboratory testing needed to document the cause of the illness.

In fact, in 1999, the CDC estimated that for each case of salmonellosis that is clinically diagnosed and reported to health officials, another 38 cases were unreported. All told, unsafe food causes tens of millions of illnesses, hundreds of thousands of hospitalisations, and thousands of deaths every year.

Leafy greens

Salads and other food items containing leafy greens - iceberg lettuce, romaine lettuce, leaf lettuce, butter lettuce, baby leaf lettuce (immature lettuce or leafy greens), escarole, endive, spring mix, spinach, cabbage, kale, arugula or chard - account for 24% of all of the outbreaks linked to the FDA Top Ten. Those outbreaks sickened over 13,568 people who were reported to have become ill - almost 30% of all the reported illnesses caused by the FDA Top Ten.

In 2006, bagged spinach contaminated with E. coli O157:H7 caused several deaths and hundreds of illnesses. That same year, E. coli O157:H7 appeared in two other outbreaks linked to leafy greens. Though produce companies have voluntarily increased their vigilance, E. coli O157:H7 is still cropping up in these products, and accounts for 10% of all outbreaks in leafy greens.

Another pathogen appearing frequently in leafy greens is Norovirus, which is commonly spread by the unwashed hands of an ill handler or consumer. This pathogen was linked to 64% of the outbreaks in leafy greens.

Salmonella was responsible for nearly 10% of the outbreaks.

Contamination may be present from production and processing, or may occur through improper handling and preparation, such as inadequate hand washing and cross-contamination of cutting boards and other equipment.

In restaurants, any of these problems in only a single food item can affect multiple patrons. For example, an outbreak of E. coli O157:H7 in 2006 began at Taco John’s, a popular Iowa eatery. Over 80 people were sickened - including two who developed potentially deadly haemolytic uremic syndrome - from contaminated iceberg lettuce from California’s Central Valley.

Overall, restaurant outbreaks accounted for almost 240 outbreaks from leafy greens. Private homes accounted for another 24 outbreaks. Notably, outbreaks in school settings tended to be quite large - averaging 89 reported illnesses per outbreak

Leafy greens can become initially contaminated on the farm through contact with wild animals, manure, contaminated water, or poor handling practices during harvest. Once they are contaminated, leafy greens can support, grow and spread pathogens until consumed. Chlorine washes and other post-harvest treatments can help reduce cross-contamination between lots, but they don’t make contaminated products truly safe to eat. In fact, bacteria can inhabit the washing systems used in making pre-washed bagged lettuce, transferring dangerous bacteria from one contaminated lot to the next, with the potential of affecting a full day’s production.

Shell eggs

The overwhelming majority of illnesses from eggs are associated with Salmonella, which sickened over 11,000 people.

Regulations for cleaning and inspecting eggs were implemented in the 1970s and have reduced salmonellosis caused by external faecal contamination of egg shells. However, Salmonella enteritidis, the most prevalent type of Salmonella in eggs today, infects the ovaries of otherwise healthy hens and contaminates the eggs before the shells are formed. Final regulations that require the adoption of controls aimed at minimising Salmonella enteriditis in egg production were issued in July 2009 (and will become effective in 2010 or 2012, depending on producer size), after over a decade of inaction by the federal government.

Half of all egg outbreaks occurred from restaurants and other food establishments.

The largest egg outbreaks occurred in prisons, with an average of 143 people reported sick in each outbreak. Catered events also had large outbreaks, averaging almost 60 people reported to have been sickened.


While a step down from leafy greens and eggs, tuna was linked to 268 outbreaks in the FDA Top Ten.

Scombroid, the illness caused by scombrotoxin, was by far the most common cause of illness related to tuna dishes, affecting over 2300 people who were reported to have been sickened, according to CSPI’s Outbreak Alert! database.

Fresh fish decay quickly after being caught and, if stored above 15.5 °C, begin to release natural toxins that are dangerous for humans. Adequate refrigeration and handling can slow this spoilage, but the toxin cannot be destroyed by cooking, freezing, smoking, curing or canning.

Symptoms of scombroid poisoning can include skin flushing, headaches, abdominal cramps, nausea, diarrhoea, palpitations and loss of vision.

As a naturally occurring toxin, scombrotoxin is foreseeable and should be properly addressed by HAACP, so tuna’s appearance in the FDA Top Ten suggests that FDA’s seafood program needs to more effectively address this hazard.

In addition to scombrotoxin, Norovirus- and Salmonella-caused illnesses related to tuna consumption, affecting nearly 1000 people.


Though they comprise a trivial part of the American diet, tainted oysters are the fourth entry in the FDA Top Ten, responsible for almost 2000 reported illnesses. Not surprisingly, the majority of outbreaks from oysters occurred in restaurants.

Illnesses from oysters occur primarily from two sources: Norovirus and Vibrio.

Although Norovirus in other foods is usually associated with improper handling during harvest or preparation, oysters can actually be harvested from waters contaminated with Norovirus.

Vibrio comes from the same bacterium family as cholera and the two most common strains in the US, V. vulnificus and V. parahaemolyticus, can both cause severe disease.


Potatoes are grown in the soil, but they are always cooked before consuming. Outbreaks are linked to dishes, like potato salad, that can contain many ingredients and also a broad range of pathogens. Salmonella is most common, associated with almost 30% of potato outbreaks.

E. coli also appears in the potato category, accounting for six potato outbreaks. Normally found in animal faeces, the presence of Salmonella and E. coli in potato dishes could indicate cross-contamination from the raw to the cooked ingredients or possibly from raw meat or poultry during handling and preparation.

Shigella and Listeria monocytogenes also appear in outbreaks associated with potatoes. Shigella is easily transmitted from an infected person to a food product, and thus may indicate improper handling during food preparation. Listeria is a stubborn bacterium that can live on deli counters and in other kitchen areas, and is often associated with cold deli salads.

More than 40% of potato outbreaks were linked to foods prepared in restaurants and food establishments (including grocery stores and delis).


Salmonella was the most common hazard among cheese products.

Cheese can become contaminated with pathogens during the initial phases of production (curdling, moulding and salting), or later during processing. Most cheeses are now made with pasteurised milk, lowering the risk of contamination with milk-borne pathogens. However, as recently as August 2009, California officials warned consumers about eating Latin American-style cheeses (such as queso fresco, queso oaxaca and others), which may be made by unlicensed manufacturers using unpasteurised milk that could contain harmful bacteria.

Linked to at least four outbreaks from cheese since 1990, listeriosis is vastly underreported, since overt symptoms of infection can be mild in those who are not particularly at risk.

Outbreaks from cheese products occur most frequently in private homes.


The largest ice-cream outbreak in history occurred in 1994, when a popular ice-cream manufacturer used the same truck to haul raw, unpasteurised eggs and pasteurised ice-cream premix. Contaminated with Salmonella en route to the plant, the premix was not pasteurised again before being incorporated into ice-cream products. The result: thousands of people sickened in 41 states.

Soft ice-cream can be a particular hazard to pregnant women and others who are more susceptible to listeriosis. A particularly hardy bacterium, Listeria can survive on metal surfaces - such as the interior of soft ice-cream machines - and may contaminate batch after batch of products.

Almost half of all ice-cream outbreaks contained in CSPI’s database occurred in private homes. This is most likely due to the use of undercooked eggs in homemade ice-cream.


Although tomatoes may have been wrongly implicated in a sweeping 2008 outbreak (later linked to fresh jalapeno and serrano peppers), tomatoes have caused at least 31 identified outbreaks since 1990.

In 2005 and 2006, for example, tomatoes were implicated in four large multi-state outbreaks of Salmonella, sickening hundreds of people.

The most common hazard associated with tomatoes is Salmonella, which accounted for over half of the reported outbreaks. Salmonella can enter tomato plants through roots or flowers and can enter the tomato fruit through small cracks in the skin, the stem scar or the plant itself.

Norovirus was the second most common hazard.


Raw and lightly cooked sprouts have been recognised as a source of foodborne illness in the US since the 1990s. Since 1999, the CDC and FDA have recommended that persons at high risk for complications of infection with Salmonella and E. coli O157:H7, such as the elderly, young children and those with compromised immune systems, not eat raw sprouts.

Although the FDA has provided guidance to sprout producers to enhance the safety of sprout products, these commodities are still causing problems.


In 1997, over 2.6 million pounds of contaminated strawberries were recalled after thousands of students across several states reported illnesses from eating frozen strawberries in their school lunches. Hepatitis A was the culprit, and contamination may have occurred through an infected worker. That same year, raspberries imported from Guatemala and Chile were implicated in an outbreak of Cyclospora across five states.

Most of these illnesses, affecting 2700 consumers, were caused by Cyclospora in berries. The resulting infection is a parasitic illness of the intestines, which can cause severe diarrhoea, dehydration and stomach cramps. Importantly, the illness does not resolve itself without antibiotics.

FDA Top Ten

The top ten riskiest foods regulated by the FDA are:

  1. Leafy greens: 363 outbreaks involving 13,568 reported cases of illness
  2. Eggs: 352 outbreaks involving 11,163 reported cases of illness
  3. Tuna: 268 outbreaks involving 2341 reported cases of illness
  4. Oysters: 132 outbreaks involving 3409 reported cases of illness
  5. Potatoes: 108 outbreaks involving 3659 reported cases of illness
  6. Cheese: 83 outbreaks involving 2761 reported cases of illness
  7. Ice-cream: 74 outbreaks involving 2594 reported cases of illness
  8. Tomatoes: 31 outbreaks involving 3292 reported cases of illness
  9. Sprouts: 31 outbreaks involving 2022 reported cases of illness
  10. Berries: 25 outbreaks involving 3397 reported cases of illness

Illnesses caused by these ten foods may be as minor as stomach cramps and diarrhoea for a day or two, or as serious as kidney failure or death. Notably, pathogens most commonly associated with meat and poultry - such as Salmonella and E. coli O157:H7 - have also been repeatedly linked to these food items. In fact, Salmonella was identified as the cause in 33% of the outbreaks from the FDA Top Ten. Other pathogens causing the outbreaks associated with these foods include Campylobacter, Scombrotoxin, Norovirus and Vibrio.

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