What do peanut butter, chocolate, ground beef, chicken, bacon, hot dogs, cheese, spinach, green onions, lettuce, tomatoes, olives, alfalfa sprouts, orange juice, apple juice, cantaloupes, raspberries, sesame tahini, ice cream, and strawberries have in common? The answer: contamination with foodborne pathogens.

Because infectious outbreaks from contaminated food are such a problem in the United States, nurses need to be familiar with the common foodborne pathogens that can be present in home, restaurant, and even hospital kitchens. With this knowledge, nurses can provide education about proper food preparation, inform special patient populations about foods to avoid, and care for patients who have contracted a foodborne illness.

Recall roll call

For a number of years, the agencies responsible for regulating the U.S. food supply, the FDA and the Department of Agriculture, have been issuing warnings about food contaminated with Escherichia coli O157:H7, Salmonella, Listeria, and Campylobacter. Just in the past 12 months, such warnings have resulted in United Food Group’s recalling 5.7 million pounds (about 2,585 tons) of E. coli O157:H7-contaminated ground beef. ConAgra Foods recalled its Peter Pan and Great Value peanut butter because of Salmonella contamination. The peanut butter-associated outbreak resulted in 628 illnesses in 47 states. A few months earlier, bagged spinach contaminated with E. coli O157:H7 sickened 199 people across 26 states. Of these people, 102 were hospitalized, 31 developed acute renal failure, and three died from hemolytic-uremic syndrome (HUS).¹ The contaminated spinach was traced back to a farm in the Salinas Valley in California, where an E. coli strain found in feces from cattle grazing near the farm matched the genetic pattern of the strain found in the bagged spinach.² Shortly after the spinach outbreak, a Salmonella outbreak linked to restaurant tomatoes caused 183 illnesses in 21 states.³ Then, green onions and lettuce were the source of two other E. coli outbreaks that sickened hundreds of Taco Bell and Taco John customers.⁴ In another, more recent recall for possible Clostridium botulinum contamination, millions of cans of sauces, chili, beef stew, corned beef hash, and other meat products sold under a multitude of brand names were pulled off supermarket shelves.

These recalls make up only a tiny fraction of the over-all problem in the United States, where each year consumption of food contaminated with microbial pathogens (bacteria, viruses, fungi, parasites, and their toxins) causes an estimated 76 million illnesses, 325,000 hospitalizations, and 5,000 deaths. These numbers were estimated from data the CDC collected more than 10 years ago,⁵ and most experts believe the problem has grown since then.

What’s more, the problem of unsafe food may continue to worsen. In 2006, 130 countries, led by Canada, Mexico, and China, shipped $60 billion of food into the United States, double the amount imported five years ago. And while the number of imports doubled, the number of inspections decreased because of funding shortfalls. Last year, only 20,662 of the 8.9 million shipments of food that arrived in U.S. ports were examined.⁶ The FDA, which is responsible for monitoring 80% of the U.S. food supply, inspects less than 1% of the food shipments that enter the United States, and between 2003 and 2006, FDA food safety inspections dropped 47% as the result of funding cuts.

But not all of the problems are from imported food. Safety tests on U.S.-produced food have dropped 75% since 2003. This decrease in FDA testing did not occur because U.S.-produced food is becoming safer.⁷ In April 2007, preliminary data from the CDC’s FoodNet surveillance system, which has collected information on foodborne illnesses from 10 states since 1996, indicated that the number of illnesses associated with three major food-related pathogens, E. coli O157:H7, Salmonella, and Listeria, increased from 2005 to 2006 while the number of illnesses caused by Campylobacter remained about the same.⁸

As an illustration of unsafe U.S.-produced food, a study in the January 2007 Consumer Reports magazine revealed that 83% of chickens (fresh whole broilers) purchased at supermarkets nationwide were contaminated with Campylobacter, Salmonella, or both — a 34% increase in contamination since a previous study, in 2003.⁹ Up to 70% of sporadic Campylobacter infections (about 1 million) in the United States can be attributed to contaminated chickens. In addition to Campylobacter, 110,000 Americans become infected with enterohemorrhagic shiga toxin-producing E. coli each year, with as many as 80 dying of the disease.¹

The most important reservoir for E. coli O157:H7 is the GI tract of cattle, and the majority of infections are the result of undercooked ground beef. However, an increasing number of E. coli O157:H7 outbreaks have been occurring as the result of fresh U.S.-grown fruit and vegetables fecally contaminated by cattle.¹ Contaminated produce is especially worrisome. Studies have shown that E. coli O157:H7 and Salmonella found in soil enriched with contaminated manure can be internalized in growing vegetables that are later often eaten raw. Internalized pathogens are impossible to remove from vegetables such as radishes, lettuce, parsley, and spinach by washing.¹⁰

This module focuses on four of the most common and serious foodborne illnesses: Salmonella, Campylobacter, E. coli O157:H7, and Listeria. Each causes an acute illness that is generally self-limiting and of short duration. However, 2% to 3% of patients (more than 2 million people each year) who contract one of these illnesses will develop secondary long-term illnesses and complications, called chronic sequellae. Examples include Guillain-Barré syndrome (GBS) after Campylobacter infections, reactive arthritis (ReA) after infections with Salmonella and Campylobacter, HUS after E. coli O157:H7 infections, and mental retardation after Listeria congenital infections.

Double the trouble: Salmonella

During the past two decades, the incidence of salmonellosis has doubled in the United States, where it’s either the first or second most common bacterial foodborne disease and the leading cause of food-related deaths.¹¹ Salmonellosis is usually contracted through eating contaminated food of animal origin (e.g., meat, poultry, eggs, and milk) or other foods (e.g., green vegetables) contaminated with animal feces during growth, transport, or processing. Each year, Salmonella cause an estimated 1.4 million infections resulting in 168,000 physician visits, 15,000 hospitalizations, and 400 deaths. The total cost for Salmonella infections in the United States is estimated at $3 billion annually.^11,12

About 2,501 Salmonella serotypes can cause human infections.¹² However, S. enteritidis and S. typhimurium are the two most common laboratory-confirmed serotypes causing foodborne infections. S. enteritidis is widespread in egg-laying and broiler poultry flocks. In chickens, the infection is localized to the ovaries, and developing eggs are contaminated before shell deposition. As a result, Salmonella can exist inside normal-appearing eggs, and if the eggs are eaten raw or undercooked, they can be the source of infection. About 10 years ago, a massive nationwide outbreak of salmonellosis occurred that was associated with contaminated raw eggs. The outbreak resulted from eating contaminated ice cream made from ice cream premix transported in tankers that had not been adequately cleaned after carrying nonpasteurized liquid eggs contaminated with S. enteritidis. More than 224,000 infections were reported.¹³

Symptoms: Salmonellosis has an incubation period of six to 48 hours after ingestion of contaminated food or water. The disease is characterized by fever (38 C to 39 C), abdominal pain, nausea, and vomiting. Stools are loose, usually without blood, and of moderate volume. The illness typically lasts four to seven days, and most people recover without treatment. After recovery, patients shed Salmonella in their stool for four to five weeks. Chronic shedding (carriage of Salmonella in stool or urine for more than a year) develops in 0.2% to 0.6% of patients.¹³

Occasionally, patients with severe diarrhea become dehydrated and require hospitalization. The elderly, infants, and immunocompromised patients, including those with lupus or AIDS, may have more severe disease. In these patients, the bacteria sometimes spread from the intestines to the blood stream. With bacteremia, metastatic infections and abscesses can occur in the heart, bones, or meninges.¹¹

HIV-infected patients have a 20- to 100-fold greater risk of salmonellosis than the general population, and the infection is more likely to cause invasive disease. Increased risk of infection also occurs in immunocompetent patients who have clinical conditions that reduce gastric acidity, such as gastric surgery. Medications that reduce gastric acidity — such as antacids or H2 blockers, such as famitidine (Pepcid), cimetidine (Tagamet), and ranitidine (Zantac) — also increase risk.

About one to four weeks after becoming infected with Salmonella, 6% to 30% of patients develop ReA, an inflammatory arthritis that occurs as a “reaction” against an infection elsewhere in the body. Symptoms include pain and swelling in the knees, ankles, and feet. Inflammation of the tendons (tendonitis) is also common as is inflammation during which tendons attach to the bone (enthesitis). The classic symptom of enthesitis is pain or irritation at the back of the heel (Achilles tendon) and at the bottom of the foot (the plantar fascia). Other nonjoint or tendon symptoms include inflammation of the urogenital tract and conjunctivitis. Fifty percent of patients with ReA recover spontaneously within six months; 50% go on to develop a chronic form of ReA.¹⁴

Treatment: Antimicrobial treatment is not recommended for uncomplicated salmonellosis. Medication does not shorten the length of illness and is associated with increased risk of positive stool cultures and relapse.¹³ However, for severe disease, patients should receive antibiotics. Antimicrobial therapy is determined by sensitivity testing. Therapy is usually with fluoroquinolones (Cipro, Levaquin) because of the widespread resistance to ampicillin (Omnipen, Principen), sulfonamides (Sulfadiazine), tetracycline (Achromycin), chloramphenicol (Chloromycetin), and ceftriaxone (Rocephin).¹¹

Campylobacter: the raw truth

Although Campylobacter species were not recognized as a cause of foodborne disease until the mid-1970s, they are now one of the most frequently identified causes of bacterial foodborne disease in the United States, with an estimated 2 million cases each year. Most cases of campylobacteriosis are sporadic or involve small family groups. The bacteria are common commensals in the GI tracts of chicken, cattle, sheep, pigs, domestic dogs and cats, rodents, and other animals. (Commensals live in host organisms without hurting or benefiting the host.) Chickens, however, are the single most important source of human infection, and over 80% of chickens purchased in U.S. supermarkets are contaminated with the bacteria. People usually acquire Campylobacter infection by eating raw or undercooked chicken or eating other foods crosscontaminated by raw chicken during preparation in a kitchen, particularly restaurant kitchens. A study of risk factors for campylobacteriosis found that 24% of the population-attributable risk for Campylobacter in the U.S. population is related to eating chicken prepared in a restaurant.¹⁵

Symptoms: The clinical features of a Campylobacter infection are not very different than those of a Salmonella infection.¹⁵ The incubation period is usually three days (range: one to seven days) before onset of disease. The most common presentation begins with diarrhea and abdominal pain. In one-third of cases there is a prodromal period of fever, headache, myalgia, and malaise 12 to 24 hours before the onset of intestinal symptoms. The prodromal period can be nasty — with high fever, rigors, generalized aches, dizziness, and delirium. Patients with prodromal symptoms tend to develop more severe disease than those who present initially with diarrhea.¹⁶ Diarrhea can range in severity from loose stools to profuse watery or grossly bloody stools with 10 or more bowel movements per day. Abdominal pain is the predominant symptom of Campylobacter enteritis, and it can be especially severe when compared to other bacterial gastroenteritis infections. Symptoms are usually self-limiting, lasting for a week.

Complications, such as ReA and GBS, can develop several weeks after infection. ReA develops in about 1% to 7% of patients. Joint pain and swelling typically appear one to two weeks after diarrhea and persist for one week to several months.¹⁴ GBS is the most dreaded complication of Campylobacter enteritis. It occurs five to 21 days after the diarrheal illness, starting with a symmetric weakness that begins in the legs and sometimes progresses to complete paralysis. Mechanical ventilation is required for up to one-third of patients who develop the syndrome. Five percent die despite respiratory care, and 20% are left with some permanent disability. In the United States, about one in a 1,000 patients with Campylobacter diarrhea develop GBS.^11,16

Treatment: For uncomplicated infections, treatment consists of rehydration and correction of electrolyte abnormalities. Antimicrobial therapy is used only for seriously ill patients who have bloody diarrhea and a worsening of symptoms or relapses. When patients need antimicrobial therapy to treat Campylobacter gastroenteritis, erythromycin (Ery-tabs) is the drug of choice. Serious systemic infections should be treated with an aminoglycoside (Amikin, Garamycin) or a carbapenem (Imipenem, Cilastin).¹⁶

Burgers and beyond: E. coli

E. coli O157:H7 (also called shiga toxin-producing E. coli, or STEC) became well-known over 20 years ago when an outbreak of severe bloody diarrhea occurred in 47 people who had eaten at the same fast-food restaurant.⁴ Since the 1982 restaurant outbreak with contaminated ground beef, E. coli have been linked to unpasterurized apple cider and milk, alfalfa sprouts, radish sprouts, salami, yogurt, cottage cheese, drinking water, potatoes, leaf lettuce, cantaloupe, and spinach. Currently in the United States, shiga toxin-producing E. coli cause more than 110,000 illnesses with about 80 deaths each year.¹

The most important source of E. coli O157:H7 for infections in humans is the GI tract of cattle. However, it can survive in environments outside the colon: E. coli O157:H7 can survive in manure in the field for more than 77 days, on onions for 85 days, and on lettuce or carrots for at least 175 days. As mentioned, the bacteria can be internalized in vegetables growing in soil enriched with contaminated manure, making it impossible to remove the E. coli O157:H7 by washing. While in the field, the bacteria can also be transmitted from fecal deposits by house flies and fruit flies to other foods, such as fruit and vegetables.¹⁰

Symptoms: The incubation period for E. coli O157:H7 is typically three to four days (range: one to nine days). Initial symptoms include watery diarrhea and cramps. Patients with more severe disease develop acute bloody diarrhea with abdominal pain and tenderness. Fever is usually absent. One-quarter to one-half of symptomatic patients with acute bloody diarrhea require hospitalization. About 5% to 15% go on to develop HUS.¹¹ A life-threatening disease, HUS is characterized by microangiopathic hemolytic anemia (destruction of red blood cells), thrombocytopenia (destruction of platelets), and acute renal failure. About 50% of patients require dialysis. The central nervous system also becomes involved. One-third of patients experience neurological symptoms including irritability, seizures, and altered mental status. HUS usually occurs five to 10 days after the onset of diarrhea. It develops when the shiga toxin enters the circulation and binds to special receptors. Shiga toxins target endothelial cells, causing vascular damage. Blood traveling through the damaged vascular system results in destruction of the red blood cells and platelets, leaving clumps of cellular debris in the capillaries. As this continues, the capillaries occlude, resulting in a decreased glomerular filtration rate and renal failure. Similar occlusions can damage the brain and other organs. Of patients who develop HUS, 3% to 5% die, and 5% to 10% of survivors will have permanent major complications, including chronic renal failure and neurological problems, such as seizures and strokes.^4,11 HUS is the most common cause of renal failure in children in the United States. Risk factors include bloody diarrhea, youth or old age (under 15 years or over 65), a short incubation period, elevated white blood cell count, high C-reactive protein, and low albumin.¹¹

Treatment: The only treatment for E. coli O157:H7 infection is supportive. Antibiotics or antimotility/antidiarrheal agents are contraindicated: Both increase the risk of HUS. Antibiotics are thought to increase production or release of toxin by E. coli O157:H7, and antimotility/antidiarrheal agents slow down intestinal motility, thereby exposing the gut to toxins for a longer time.

Listeria: a trip to the hospital

Although Listeria causes less than 1% of reported foodborne illnesses, it accounts for about 28% of all deaths from foodborne infections. It also has the highest hospitalization rates of all foodborne pathogens (91%).¹⁷

Nearly all Listeria infections are acquired by eating contaminated foods, especially hot dogs, Mexican-style soft cheeses, processed deli meats, smoked seafood, meat spreads, prepackaged turkey sandwiches, and pâtés. Listeria can grow at refrigeration temperatures, in acidic concentrations of a pH of 5 or higher, and in salt concentrations as high as 12%. The bacteria are typically found in ready-to-eat food that has been refrigerated for prolonged periods.¹⁸

The majority of infections in healthy adults are asymptomatic or at most a mild influenzalike illness — a self-limited febrile gastroenteritis that lasts two or three days. In fact, a significant proportion of healthy adults (5% to 10%) carry Listeria in their GI tract without showing any signs of illness.¹⁹

However, Listeria can cause serious clinical illnesses in immunosuppressed patients, neonates, the elderly, pregnant women, and people taking corticosteroids. In these hosts, the bacteria can cause meningitis, meningoencephalitis, and bacteremia. Pregnant women in their third trimester are especially susceptible and account for up to one-third of reported cases.¹⁷ Listeria can cross the placental barrier to cause amnionitis, premature labor, spontaneous abortion, stillbirth, and infection of the neonate. Listeria can also cause granulomatosis infantiseptica, a severe in utero inflection in which infants develop overwhelming disseminated disease with abscesses and granulomas in multiple organs. Most neonates with the infection are stillborn or die soon after birth.¹⁹

In nonpregnant adults, corticosteroids are the most important predisposing factor for Listeria infections. In these patients, bacteremia is the most common manifestation of invasive disease. Patients typically present with fever, myalgias, arthralgias, headache, and backache. In patients with underlying neoplastic disease and in those receiving corticosteroids, the bacteria can disseminate to the brain or meninges, causing meningitis or meningoencephalitis. Patients with meningitis present with altered consciousness, seizures, and movement disorders.¹⁹ Listeria is the fifth most common cause of meningitis, and meningitis caused by Listeria has the highest mortality rate of all meningitis, 22%. In patients with meningoenchephalitis caused by Listeria, the mortality rate ranges from 36% to 51% despite appropriate antibiotic treatment.^17,18

Treatment: Ampicillin is the preferred drug with the addition of gentamicin (Garamycin) for patients with meningitis.¹⁹

Foodborne illnesses are common, but the majority are transient and resolve within a few days. On occasion, however, eating contaminated food can be a costly experience that results in long-term medical complications or death. For all of us, and especially for people who are immunocompromised, knowing how to prevent foodborne diseases is of utmost importance.

Nurses can provide this information to patients and their families. Education is particularly important when food is being prepared for people who are elderly or very young, pregnant, or immunocompromised by diseases or medications. Because foodborne infections can be life-threatening for many people, nurses should encourage patients to take the following precautions when preparing food: 1) practice good personal hygiene; 2) cook foods adequately; 3) avoid crosscontamination; 4) keep food at safe temperatures; and 5) avoid foods that are likely to be contaminated with pathogens. Patients who are especially vulnerable to infection should be advised to avoid the following foods:

• Raw or undercooked meat, poultry, and fish
• Unpasteurized milk and milk products
• Raw or undercooked eggs or foods containing raw eggs
• Soft cheeses, such as Mexican-style cheeses, feta, and Brie
• Raw sprouts of all types
• Unpasteurized fruit juices
• Contaminated water

In addition, patients at high risk of listeriosis should be advised to reheat foods such as hot dogs, deli-style meats, and poultry products to 165 F before eating them.²⁰ Patients should be cautioned that fresh produce may be contaminated and to handle it with care. All fresh produce should be carefully washed, including cantaloupes and watermelons.

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