Published: August 2010
Foodborne disease is a pervasive problem caused by consumption of contaminated food and drink. More than 200 pathogens are associated with foodborne disease. An estimated 76 million cases occur annually (one in every four Americans), resulting in 300,000 hospitalizations and 5,000 deaths.1 Fewer cases are documented because of underreporting. International travel and food importation have further expanded the problem. The onset of foodborne disease is generally acute, with resolution of an uncomplicated illness in 72 hours for most episodes. Proper food handling and preparation, personal hygiene, and improved methods of decontamination of consumer products could significantly reduce the extent of morbidity and mortality of this common problem.
Foodborne illness is tracked in the United States through a system called FoodNet, a joint effort of the U.S. Food and Drug Administration (FDA) and the U.S. Department of Agriculture (USDA). Data are collected annually from ten different monitoring sites throughout the country (representing 15% of the population) and compiled by the Centers for Disease Control and Prevention (CDC). Only documented cases are used for reporting. The target organisms include Campylobacter spp., Salmonella spp., Shigella spp., Listeria spp., Shiga toxin-producing Escherichia coli O157:H7 (STEC O157), non-O157 STEC, Vibrio spp., Yersinia spp., Cryptosporidium spp., and Cyclospora spp. The hemolytic-uremic syndrome (HUS) is also tracked.
Foodborne disease can be caused by bacteria, parasites, toxins, and viruses (Box 1). Despite efforts to investigate foodborne disease, less than 50% of all outbreak causes are identified, usually because of limited diagnostic capabilities. Viruses are likely the most common cause of foodborne disease but are seldom investigated and confirmed because of the short duration and self-limited nature of the illness. In addition, the inherent difficulty of laboratory investigation and subsequent cost of viral studies lead to a lack of clinician investigation and therefore overall underreporting. Bacteria are the most common documented cause.
Cultural and demographic factors, as well as increased mobility, have resulted in major epidemiologic shifts in foodborne disease during recent decades.2 Previous outbreaks of foodborne disease were smaller and limited in scope, more often originated in the home, and were associated with Staphylococcus or Clostridium spp. Family picnics or dinners and home-canned foods were the typical sources for the outbreaks. Today, many more people dine outside the home and travel more extensively. As a result, more than 80% of foodborne disease cases occur from exposures outside the home.
|Box 1: Common Causes of Foodborne Disease
Shigella spp. STEC O157:H7
Paralytic shellfish toxin
© 2004 The Cleveland Clinic Foundation.
Technology has provided the means for mass production and distribution of food. Therefore, foodborne disease often occurs on a massive scale, whereby hundreds or thousands are exposed and may become ill. Mobility and travel have resulted in exposure to foods abroad, where regulation of food safety and food products for sale may vary. When traveling, the axiom “boil it, peel it, cook it, or forget it” remains true in many areas of the world. Travelers bringing home unique foods as gifts may unwittingly expose family members and friends to unexpected illness. International ships discharging their bilge in ports are another possible means of disseminating pathogens.
Food importation has steadily increased to meet the demand for seasonal and nonseasonal foods. Conditions of production and harvest may be unsupervised or uncontrolled, with resultant importation of contaminated foods. Raw manure is frequently used as fertilizer, causing contamination of fresh produce. If improperly cleaned, the fertilized produce may cause illness when consumed.
Unique ethnic food preferences and preparation have been associated with several food-related illnesses. One example is the African American tradition of eating chitterlings (cooked swine intestines) during the Christmas holiday season.3 This food has been associated with an outbreak of Yersinia enterocolitica infection in infants.4 Fresh cheese made from unpasteurized milk has been associated with episodes of listeriosis in Hispanic neighborhoods.
Foodborne disease is more likely to affect the extremes of age as well as immunocompromised patients and pregnant women. These groups suffer higher incidence, morbidity, and mortality.5,6 The effect of foodborne disease may extend beyond the immediate illness. This has been shown by a Danish study, which demonstrated a greater than threefold risk of dying in the year after contracting a foodborne illness.7
Most foodborne disease has a short duration of illness and a self-limited course. Others may cause a more protracted illness, such as Cryptosporidium and Cyclospora. However, some foodborne diseases are associated with long-term chronic sequelae (Box 2). Salmonella, Shigella, Yersinia, and Campylobacter spp. are linked to reactive arthritis; Campylobacter has also been associated with the Guillain-Barré syndrome, and STEC O157:H7 has been linked to renal failure.8
|Box 2: Sequelae of Foodborne Illness
|Hemolytic-Uremic Syndrome, Renal Failure|
© 2004 The Cleveland Clinic Foundation.
The most commonly identified pathogens are Campylobacter spp., Salmonella spp., Shigella spp., and STEC O157:H7. These organisms have evolved and now have greater cold, heat, and acid tolerance, as well as resistance to multiple antibiotics. Increased drug resistance has been associated with prolonged illness and a greater risk of hospitalization.9
Almost any food can be a source of foodborne disease. Some foods are more commonly associated with particular organisms (Box 3). Salmonella has traditionally been associated with poultry and eggs, Campylobacter with chicken and unpasteurized milk, and STEC O157:H7 with ground beef. An outbreak of STEC O157:H7 was associated with steak that had been needle-tenderized, thereby exposing the center of the meat to surface organisms. When the steak was not thoroughly cooked to an adequate internal temperature, the microorganisms survived and illness occurred after consumption.
|Box 3: Pathogens and Food Associations
|Campylobacter: chicken, unpasteurized milk and dairy products, water|
|Salmonella: eggs, poultry, fruits, vegetables, meats|
|Shigella: fruits, vegetables|
|Escherichia coli O157:H7: hamburger, salami, alfalfa sprouts, unpasteurized milk and dairy products and juice|
|Clostridium botulinum: home-canned foods|
|Listeria monocytogenes: delicatessen meats, soft cheeses, unpasteurized milk and dairy products, vegetables|
|Vibrio vulnificus: shellfish|
|Yersinia enterocolitica: raw pork, unpasteurized milk and dairy products, water|
© 2004 The Cleveland Clinic Foundation.
Water may be the vector of illness when contaminated with viruses, bacteria, parasites, or chemicals. Crowding, poor sanitation, disruption of water supplies, and natural disasters are closely linked to waterborne illness. Viruses are the most common cause of waterborne illness and include rotaviruses, enteric adenovirus, astrovirus, caliciviruses and hepatitis A virus. Outbreaks of gastroenteritis aboard cruise ships in recent years were a result of noroviruses. Salmonella spp., Shigella spp., E. coli, and Vibrio spp. are the predominant bacterial pathogens involved. Cryptosporidium spp. and Giardia lamblia are the parasitic pathogens most commonly encountered in water-borne illness. Immunocompromised hosts, particularly organ transplant recipients and HIV-infected patients, should exercise extra precaution in situations of potential waterborne illness.
Incubation periods of foodborne disease may offer clues to the cause. Four time frames may be envisioned: very brief, short, intermediate, and long durations of incubation. The very brief category (<8 hours) is generally caused by preformed toxins, which may be found in staphylococcal or bacillus-contaminated food. Short incubation periods (24-48 hours) are more typical of viral causes. Intermediate incubation periods (1-5 days) correlate with many bacterial pathogens. The long-duration incubation group (>5 days) approximates the time course of parasitic infections. These time frames are crude groupings and areas of overlap exist between them. In addition, the inoculum of organisms ingested may influence the incubation period and the rapidity of onset of illness—for example, a large inoculum may cause a shortened time to onset of illness.
Bloody diarrhea or a febrile illness is often associated with invasive organisms. The more common microorganisms associated with bloody diarrhea and fever are listed in Box 4.
|Box 4: Clinical Manifestations
© 2004 The Cleveland Clinic Foundation.
Diagnosis is accomplished through a careful history, physical examination, and laboratory evaluation. The history should include questioning about the suspected time of exposure, recent travel, the food and drink consumed, other people who may have been present and eaten similar foods, and the specific symptoms involved (e.g., nausea, vomiting, diarrhea with or without visible blood, cramping, gas, fever, neurologic symptoms, alteration of mental status). Dietary history may include intake during the last 2 to 3 weeks. The physical examination should focus on vital signs, including orthostatic measurements, skin turgor, mental status, abdominal findings, and stool testing for blood. Fresh stool samples for culture and analysis (<6 hours old) provide the highest yield. The clinician must be knowledgeable of the laboratory's assay procedures to facilitate proper sample testing. Specific culture requests for suspected organisms may be necessary, as well as microscopic examination of stool samples for parasites. Three samples on different days will generally provide adequate diagnostic results. Special circumstances may dictate the need to perform special assays for toxins (e.g., botulinum toxin) on gastric aspirates or stool samples. Blood cultures are often useful, particularly if Salmonella or Listeria is suspected or when evaluation involves high-risk groups and immunocompromised hosts.
Most foodborne disease is self limited and requires only supportive care. The very young, older adults, immunocompromised patients, and pregnant women may benefit from antibiotic treatment for certain bacterial or parasitic infections. Drug-resistant pathogens require knowledge of regional, national, and international patterns of resistance to allow appropriate empirical selection of therapy.
The most recent FoodNet data list nontyphoidal Salmonella as the most commonly identified bacterial cause of foodborne disease.10 It is estimated that 1,400,000 cases occur annually. Fever, abdominal cramps, and diarrhea (occasionally bloody in a minority of cases) are the usual manifesting symptoms after 8 to 48 hours of incubation. Although generally self limited, Salmonella infection may cause sepsis and localized infections, such as septic arthritis and infection of endovascular prosthetic devices, such as grafts. The most common serotypes are Salmonella typhimurium and S. enteritidis.
Eggs remain a common source because of vertical transovarial transmission within an infected poultry flock. Poultry itself has become a significant source of Salmonella infection. Fruits, vegetables, meats, and ice cream are other reported food associations.
Populations at greatest risk are infants, older adults, and the immunocompromised, but also those with inflammatory bowel disease, hemoglobinopathies, and endovascular prosthetic devices. Patients older than 60 years have the highest rate of hospitalization and highest case-fatality rate.11 Antibiotic treatment should be considered for these high-risk groups because bacteremia may occur in 2% to 14% of cases. Unfortunately, increasing resistance to the usual antibiotics (cephalosporins, aminoglycosides, and fluoroquinolones) has made therapy more challenging.
Campylobacter is the second most common identified organism in foodborne disease. Over one million cases are estimated to occur annually. After a 2- to 5-day incubation period, acute dysentery ensues. Nearly two thirds of patients will have fever, and one half will have bloody diarrhea. Illness may last 1 week and then resolve spontaneously. Immunocompromised patients may experience life-threatening sepsis and therefore should receive aggressive therapy.
Age-related biphasic peaks of Campylobacter infection occur in infancy and early adulthood. Young men are more often affected because of poor food handling knowledge. Almost all human illness is caused by one species, Campylobacter jejuni. Poultry is the overwhelming source. Additional food sources include raw milk, water, and ice cream. When treatment is deemed necessary, a macrolide is preferred or a fluoroquinolone antibiotic can be used, but once again increasing drug resistance may present a therapeutic challenge. Macrolide resistance remains less than 5% but quinolone resistance may be as high as 20%. Regions of southeast Asia have strains of Campylobacter that are resistant to both macrolide and quinolone antibiotics. Antibiotic-resistant strains are associated with more invasive disease and increased mortality.12 Guillain-Barré syndrome may be an unusual delayed sequela of infection with Campylobacter.
Although less common than Salmonella or Campylobacter, Shigella is a significant cause of foodborne disease. Shigella is responsible for 10% to 20% of cases of bacterial foodborne illness each year in the United States. After 2 to 4 days of incubation, it produces an invasive dysentery syndrome that often includes fever and bloody diarrhea. Shiga toxins are frequently elaborated. Duration is typically 5 to 7 days. Fruits, vegetables, and shellfish are common food associations. Third-generation cephalosporins and fluoroquinolones are the antibiotics of choice; however, drug resistance may be encountered. Long-term sequelae include reactive arthritis and HUS.
STEC O157:H7 infection was initially associated with ground beef. Multiple other food associations have been recognized, such as unpasteurized apple cider, milk and dairy products, juices, and lettuce. In addition, STEC O157:H7 has been associated with non-foodborne illness after contact with cattle and swimming in contaminated lakes. Crump and colleagues13 have described an outbreak among a group after they visited a dairy farm.
An estimated 60,000 to 70,000 cases occur annually, resulting in approximately 2000 hospitalizations and 60 to 70 deaths. The average incubation period is 4 to 8 days. Symptoms include abdominal cramps with bloody diarrhea but little or no fever. The diarrhea usually resolves within 1 week. Antibiotics appear to play no role in treatment, because the illness is the result of a Shiga toxin produced by the organism. Five to 10 days after the diarrheal illness, HUS develops. It is more common in the young (<5 years old) and older adults. Manifestations of HUS may include hemolytic anemia, thrombocytopenia, and acute renal failure. Neurologic sequelae (e.g., seizures or stroke) may be additional late complications.
Listeriosis is caused by Listeria monocytogenes. It is a much less common cause of foodborne disease, with approximately 2500 cases annually. However, it has the highest hospitalization and mortality rates of all foodborne diseases, with approximately 500 deaths each year. It strikes more often at the extremes of age, attacking the young and older adults, as well as those who are immunocompromised, causing a more severe illness in this population. Pregnant women are also at increased risk of infection. Manifestations appear to vary by host-related factors. Older adults and immunocompromised patients often present with sepsis and meningitis, whereas immunocompetent patients develop febrile gastroenteritis. Pregnant women may experience a flulike illness, but granulomatosis infantisepticum may afflict the fetus, resulting in bacteremia, meningitis, or both in the newborn infant.
Data from the CDC have suggested that Latin Americans may have a higher incidence of listeriosis. Latin American women of childbearing age and their infants have an 11-fold increased risk of infection.14 The reason for this finding is unclear and remains under investigation.
Listeriosis has been associated with delicatessen meats, hot dogs, soft cheeses, and unpasteurized milk and dairy products. Queso fresco, an ethnic homemade soft cheese produced from unpasteurized milk, has been associated with listeriosis in the Hispanic population.
Illness follows a 1- to 2-day incubation period. Clinical symptoms include fever, gastrointestinal upset, and subsequent diarrhea. When treatment is needed, ampicillin appears to be the most effective antibiotic.
Vibrio foodborne disease tends to be seasonal, with a peak incidence in late summer and early autumn. Consumption of raw seafood from the southern United States coast is the most common food association. V. parahaemolyticus and V. vulnificus are the most frequent species isolated. They are halophilic and cold-tolerant organisms, which allow Vibrio to survive in conditions that may normally retard or prevent food contamination.
A clinical syndrome of watery diarrhea, abdominal cramping, nausea, vomiting, and fever occurs 1 to 4 days after ingestion. The illness is usually self limited, with resolution in about 3 days. Persons with liver disease may develop a severe sepsis syndrome, bullous cellulitis, or both, with 50% mortality. Vibrio cellulitis and wound infections are occupational risks for fishermen and oyster shuckers. Appropriate antibiotic treatment includes tetracycline or ceftriaxone.
Yersiniosis is an uncommon cause of foodborne disease in the United States. It has been associated with the consumption of raw pork, unpasteurized milk and dairy products, and contaminated water. The preparation, handling, or consumption of chitterlings (see earlier) has been associated with Yersinia infections. Young African American children are disproportionately affected by this holiday food tradition.
The incubation period is 4 to 7 days and is followed by fever, abdominal pain, and bloody diarrhea. The abdominal pain may mimic that of appendicitis. Additional manifestations include carditis, joint pain, and sepsis. Although most cases resolve spontaneously, severe cases may require therapy with doxycycline, a fluoroquinolone, aminoglycoside, or trimethoprim-sulfamethoxazole.
Parasites are an uncommon form of foodborne illness. The most frequent causes include Cryptosporidium spp. and Giardia lamblia, which have been associated with contaminated water. Additional foodborne diseases include cyclosporiasis, trichinosis, toxoplasmosis, and amebiasis. Cyclosporiasis has been previously linked to imported raspberries. Trichinosis was traditionally linked to pork but can be contracted through other sources, such as inadequately cooked wild game. Toxoplasmosis has been most often associated with undercooked meat and amebiasis is associated with contaminated water.
Cryptosporidiosis may be difficult to treat. Response has been noted with nitazoxanide, paromomycin, or azithromycin. Metronidazole is the usual treatment for giardiasis. Prolonged treatment with trimethoprim-sulfamethoxazole may be necessary to cure cyclosporiasis.
Foodborne disease caused by toxins may have a variety of presentations that include gastrointestinal symptoms, neurologic manifestations, or both. Preformed heat-stable enterotoxins associated with Staphylococcus aureus and Bacillus cereus have an acute onset of nausea, vomiting, and diarrhea within 1 to 6 hours of ingestion. Fever is not a common component of this self-limited syndrome. Symptoms resolve rapidly, often within 12 hours.
Clostridium perfringens has a slower onset of illness, occurring approximately 12 hours after ingestion, because the heat-labile enterotoxin is produced in vivo after consumption of contaminated food. Cramping and diarrhea are the major manifestations, with resolution of symptoms in about 24 hours.
Botulinus toxin is considered the most potent lethal substance known. It is produced by Clostridium botulinum. Illness occurs 18 to 36 hours after ingestion of the source food. Home-canned foods have been the traditional sources. The onset of illness is heralded by nausea, vomiting, and diarrhea, followed by constipation. A descending paralysis then occurs. Antitoxins are available but only prevent further progression of paralysis because they neutralize circulating toxin and have no effect on bound toxin. Foodborne botulism carries a 5% to 10% mortality rate. If the individual survives, many months may be required before recovery.
The onset of paresthesias within minutes to a few hours of food ingestion should alert the clinician to the possibility of niacin, monosodium glutamate, fish, or shellfish poisoning. Marine bacteria present on the surface of some fish produce inhibitors of histamine degradation, resulting in high levels of histamine. When they are consumed, scombroid poisoning (histamine fish poisoning) may occur. The fish most often associated with scombroid poisoning are tuna, mackerel, skipjack, bonito, and mahi-mahi. The syndrome resembles a histamine reaction, with flushing, headache, nausea, vomiting, cramping, and burning in the mouth and throat. Poisoning by ciguatera fish such as grouper and snapper produces nausea, vomiting, and diarrhea as well as paresthesias of the lips, tongue, and throat. Shellfish poisoning causes a similar syndrome except that muscle weakness, paralysis, or amnesia may occur in severe cases. The neurologic manifestations resolve in hours to a few days.
Mushroom poisoning can produce various clinical syndromes. Depending on the toxin involved, symptoms may range from parasympathetic hyperactivity to hallucinations or hepatic and renal failure, in the case of amatoxins or phallotoxins. Onset is rapid, within 2 hours of ingestion, and resolution of symptoms occurs in approximately 24 hours. Organ failure may follow after an additional 1 to 2 days. Without emergent liver transplantation, acute hepatic failure rapidly leads to death.
Hepatitis A and Norwalk virus are the two most commonly identified viral sources of foodborne disease. Many additional cases of foodborne disease occur as a result of unidentified viruses. Hepatitis A is often associated with shellfish and infected food handlers. In addition, green onions were determined to be the source of a widespread outbreak in a restaurant chain in 2003.15
The high morbidity and overall relatively low mortality of foodborne disease could be significantly reduced. Proper knowledge of food handling, storage, and preservation could have a significant impact on the occurrence of this common problem. Improved conditions in mass production and processing of foods have produced tangible results. New methods of sterilization, such as irradiation, represent avenues of future progress.
Additional information on foodborne illness can be found on the CDC website.16 This site reviews many of the common syndromes in an educational case scenario format. Several useful tables list causative agents, incubation periods, and major manifestations.