- Email: [email protected]
Food-Borne Illnesses
Clinical Microbiology Newsletter Vol. 33, No. 6
www.cmnewsletter.com
$99 March 15, 2011
Food-Borne Illnesses Andrea J. Linscott, Ph.D., D(ABMM), Ochsner Medical Center, Department of Pathology, New Orleans, Louisiana
Abstract Millions of cases of food-borne illnesses occur annually in the United States. These food-borne illnesses can range from mild aggravations to life-threatening situations. Clinical microbiology laboratories play an important part in the detection of these illnesses by identifying and reporting the infections to public health officials, who use the data to detect food-borne outbreaks. This article highlights the more common causes of food-borne illness, symptoms, diagnosis, and prevention. The Centers for Disease Control and Prevention (CDC) estimates that 76 million cases of food-borne illnesses occur annually in the United States (1). The case numbers are based on reportable diseases that each laboratory is required to report to their local or state public health office and by active surveillance conducted by the CDC. Food-borne illnesses can be caused by a variety of substances. As microbiologists, we clearly associate food-borne illnesses with the consumption of contaminated food or beverages that contain bacteria, viruses, or parasites. However, there are non-infectious causes of foodborne illnesses, like chemicals and toxins, that occur as well (2). The majority of food-borne illnesses have either a bacterial or viral etiology. A list of the more common causative agents can be found in Table 1 (3-5). Symptoms of food-borne illnesses may include nausea, vomiting, and diarrhea, which typically last for 2 to 3 days in most individuals. However, severe complications can occur from food-borne illnesses in certain patients. These Corresponding Author: Andrea J. Linscott, Ph.D., D(ABMM), Ochsner Medical Center, Department of Pathology, 1514 Jefferson Highway, New Orleans, LA 70121. Tel.: 504-842-2171. Fax: 504-842-3515. E-mail: [email protected]
Clinical Microbiology Newsletter 33:6,2011
severe complications may include stillbirths, hospitalization due to sepsis, hemolytic uremic syndrome, Reiter’s syndrome (reactive arthritis), GuillanBarré syndrome (nerve paralysis), and/ or death. Table 1 also illustrates that severe complications are often associated with certain patient populations such as the very young or older patients or patients with underlying conditions and infections with certain organisms. Some examples of organism/complication correlations are Listeria – stillbirths, Shiga-toxin producing Escherichia coli (STEC) – hemolytic uremic syndrome, and Vibrio vulnificus sepsis in alcoholic patients. Preliminary data from FoodNet, a collaborative program comprised of 10 state health departments, CDC, the Food and Drug Administration, and the U.S. Department of Agriculture’s Food Safety and Inspection Service, listed the most common pathogens for food-borne illnesses for 2009, from highest to lowest incidence, as Salmonella, Campylobacter, Shigella, Cryptosporidium, STEC O157, STEC non-O157, Vibrio, Listeria, Yersina, and Cyclospora (6). Compared to previous years, there has been an increased incidence of Vibrio, while there has been a decrease in Shigella and STEC O157. These data also show that children less than 4 years © 2011 Elsevier
of age have the highest reported incidence of food-borne illnesses; however, adults 50 years of age have the highest hospitalization and fatality rates (6). The organisms that were most responsible for hospitalization of adults, in descending order, are STEC O157, Salmonella, Yersinia, Vibrio, STEC non-O157, Shigella, Cyclospora, Cryptosporidium, and Campylobacter. Listeria had the highest fatality rate in adults over 50, followed by Vibrio (6). Food-borne outbreaks are defined by the CDC as the “occurrence of two or more similar illnesses resulting from the ingestion of a common food.” When food products have been identified as a causative agent in a food-borne outbreak or if quality control measures during food processing indicate potential contamination, the food or beverage product may be recalled. A review of information from the U.S. Food and Drug
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Table 1. Common causative agents of food-borne illnesses Incubation period
Organism
Signs and symptoms
Epidemiology
Laboratory diagnosis
Bacillus cereus – preformed enterotoxin, emetic type
1 to 6 h
Sudden onset of nausea and vomiting, with or without diarrhea
Cooked foods, like meat or fried rice, that have not been properly refrigerated
Usually not performed; stool and food sources may be needed for public health investigation.
Bacillus cereus – diarrheal type
8 to 16 h
Abdominal pain with diarrhea
Variety of foods from meat, vegetables, pasta, deserts, cakes, sauces, milk
Usually not performed; stool and food sources may be needed for public health investigation.
Brucella sp.
7 to 21 days
Fever, night sweats, backache, muscle aches, diarrhea
Raw milk or other unpasteurized dairy products, meat
Positive serology and/or blood culture(s)
Campylobacter jejuni
2 to 5 days
Fever, abdominal cramping, diarrhea with or without blood; Guillan-Barre syndrome can be seen in some individuals.
Raw and undercooked poultry, unpasteurized milk, contaminated water
Stool culture with specific medium, temperature, and atmospheric conditions; rapid immuno-chromogenic tests or molecular assays
Clostridium botulinum – preformed toxin
12 to 72 h
Abdominal cramping, nausea, vomiting, diarrhea, double vision; death or long term nerve damage may be seen.
Improperly canned foods, herb-infused oils, baked potatoes in aluminum foil
Toxin testing of serum, stool, and/or food performed at some state health department laboratories or CDC
Clostridium botulinum – infant
3 to 30 days
Floppy baby syndrome – lethargy, weakness, poor head control; constipation, poor feeding and sucking reflexes
Honey, home-canned vegetables and fruits, corn syrup
Toxin testing of serum, stool, and/or food performed at some state health department laboratories or CDC
Clostridium perfringens – toxin
8 to 16 h
Diarrhea, abdominal cramping, and nausea
Meat, poultry, gravy, inadequately reheated food
Test stool for enterotoxin; not routinely performed in most clinical laboratories
Cryptosporidium sp.
2 to 10 days
Watery diarrhea, abdominal cramps; severity depends on host immune status.
Undercooked food or food contaminated by ill food handler, contaminated drinking water
Detection of oocysts in stool using modified acid-fast stain, direct fluorescent antibodies, or with immunoassays
Cyclospora cayetanensis
1 to 14 days
Watery diarrhea, abdominal pain, nausea, loss of appetite, and weight loss
Fresh fruits and vegetables
Detection of oocysts in stool using modified acid-fast stain
Enterohemorrhagic E. coli – O157:H7 and other Shiga toxins
1 to 8 days
Bloody diarrhea, abdominal pain and vomiting; fever may be absent; hemolytic uremic syndrome.
Undercooked beef, unpasteurized milk and fruit juices, raw fruits, and vegetables
Isolation of the organism from stool culture using Sorbitol MacConkey or CHROMagar media; confirmation using antisera or latex agglutination; detection of the shiga toxins by immunoassay testing
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© 2011 Elsevier
Clinical Microbiology Newsletter 33:6,2011
Table 1. Common causative agents of food-borne illnesses (continued) Organism
Incubation period
Signs and symptoms
Epidemiology
Laboratory diagnosis
Hepatitis A virus
15 to 50 days
Diarrhea, jaundice, dark urine, fever, headache, nausea, and abdominal pain
Raw product, contaminated drinking water, food contaminated by infected food handlers, and shellfish from contaminated water
Increase in ALT and bilirubin; serology test: positive IgM and anti-hepatits A antibodies
Listeria monocytogenes
9 to 48 h (gastrointestinal) 2 to 6 wk (invasive disease)
Diarrhea, fever, muscle ache, and nausea; pregnant women may have mild flu-like symptoms, and infection may lead to premature delivery or stillbirth. Meningitis and sepsis may be seen in elderly or immunocompromised individuals.
Unpasteurized milk, soft cheese made with unpasteurized milk, ready-to-eat deli meats and hot dogs
Blood and cerebrospinal fluid cultures; antibodies to listerolysin O; stool culture may not be useful, as asymptomatic carriage does occur.
Noroviruses
12 to 48 h
Nausea, vomiting, diarrhea, abdominal pain, fever, and headache
Raw produce, contaminated drinking water, food contaminated by infected food handler, shellfish from contaminated water
Reverse transcription PCR performed on fresh, unpreserved stool samples; negative stool cultures and fecal stain for white blood cells
Salmonella spp.
1 to 3 days (non-Typhi) 3 to 60 days (Typhi)
Non-Typhi: diarrhea, fever and abdominal cramps Typhi: Fever, chills, anorexia, malaise, constipation, and myalgia
Contaminated eggs; poultry; unpasteurized milk, dairy products, or juice; contaminated raw fruits and vegetables
Stool cultures (non-Typhi) Stool and blood cultures (Typhi)
Shigella spp.
24 to 48 h
Diarrhea (+/- blood and mucus), fever, and abdominal cramps
Food or water contaminated by fecal material; food contaminated by infected person
Stool culture
Staphylococcus aureus (preformed enterotoxin)
1 to 6 h
Sudden onset of nausea and vomiting and abdominal cramps; fever and diarrhea may be present.
Unrefrigerated or improperly refrigerated meats, potato and egg salads, or cream pastries
Clinical diagnosis; toxin can be tested from stool, vomitus, or food through public laboratory or reference laboratory.
Trichinella spiralis
1 to 2 days for intestinal symptoms; 2 to 4 wk for systemic symptoms
Acute phase: nausea, diarrhea, vomiting, fatigue, abdominal pain. Systemic phase: muscle soreness, periorbital edema, eosinophilia, occasional cardiac and neurologic abnormalities
Raw or undercooked contaminated meat (pork, bear, walrus, moose), crosscontaminated ground beef, lamb
Positive serology, demonstration of larvae in muscle biopsy specimens, increase in eosinophils
Vibrio cholerae (O1, O139) (non-O1 or non-O139)
24 to 72 h
Profuse watery diarrhea, vomiting; dehydration and death can occur within several hours.
Contaminated water, raw fish, shellfish, and crustaceans
Stool culture, including thiosulfate citrate bile salts sucrose agar (request needed to include specific media)
Vibrio parahaemolyticus
2 to 48 h
Watery diarrhea, abdominal cramps, nausea, vomiting
Raw or undercooked seafood or cooked seafood contaminated with seawater
Stool culture, including thiosulfate citrate bile salts sucrose agar (request needed to include specific media)
Vibrio vulnificus
1 to 7 days
Vomiting, diarrhea, abdominal pain, possible sepsis (especially in alcoholic patients or patients with liver problems)
Raw or undercooked seafood or cooked seafood contaminated with seawater
Stool culture, including thiosulfate citrate bile salts sucrose agar (request needed to include specific media)
Yersinia enterocolitica
24 to 48 h
Diarrhea, vomiting, fever, abdominal pain (may mimic appendicitis)
Undercooked pork, unpasteurized milk, tofu, contaminated water, chitterlings
Stool or blood cultures, including cefsulodin-irgasannovobiocin agar or routine stool media held at appropriate temperature
Clinical Microbiology Newsletter 33:6,2011
© 2011 Elsevier
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Administration Safety Recall website shows that for 2010, were been over 100 recalls due to “possible health risks” (7). Salmonella was the organism most commonly linked with food product recalls. In 2010, over 550 million eggs were recalled due to possible Salmonella contamination, resulting in one of the largest massive recalls (7). Other products recalled due to potential Salmonella contamination were headcheese, pickles, salami, raw tuna, frozen dinners, alfalfa sprouts, lettuce, tomatoes, and olives (7). Interestingly, there have been numerous recalls of pet food and pet treat products for Salmonella contamination (7). Pet food contamination is not usually a problem for the family pet but for the human who is handling the food product or treat and then not adequately washing their hands afterwards. A typhoid outbreak was associated with mamey pulp used in frozen drinks. In October 2010, there was a Listeria monocytogenes outbreak related to celery contamination in a processing plant, and at the time of this writing, 5 people had died from that outbreak (8). Numerous recalls of beef have been linked to E. coli O157:H7 contamination. In addition, buffalo meat and fruit compote have been linked to E. coli O157 outbreaks (7). An outbreak in a hospital cafeteria, in which one person died, was related to chicken salad contaminated with Clostridium perfringens (7). Norovirus was responsible for an outbreak at an Ivy League faculty club, as well as at the 2010 American Society for Microbiology Annual meeting (7). I can personally attest to the ASM outbreak, as I was one of the participants who became ill.
Epidemiology of Contaminated Food Food can become contaminated in several different ways. The source of the organism can be a healthy animal’s gastrointestinal tract, and those organisms may contaminate the animal carcass during slaughter. If that contaminated carcass is not thoroughly cooked, the organisms can be transmitted to humans. Examples of this type of transmission are Salmonella and Campylobacter found in chicken or E. coli O157 found in beef that has not been adequately cooked. Contamination of fruits and vegetables can occur when 44
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water contaminated with human or animal fecal material is used to irrigate the produce. Food handlers can spread organisms such as Shigella, hepatitis A virus, or norovirus via the fecal-oral route or when they have skin lesions caused by an organism like Staphylococcus aureus. Improperly cleaned cooking utensils and/or contaminated kitchen counters can aid in the transmission of these organisms that cause food-borne illness. During certain times of the year, shellfish and oysters harbor higher numbers of Vibrio species than normal, and eating them should be avoided during these times. Organisms like L. monocytogenes and Yersinia enterocolitica can actively multiply in foods, like deli meats and unpasteurized milk products, stored at refrigerated temperatures. Clostridium species and Bacillus cereus can produce toxins in food kept at inadequate temperatures or produce spores that are ingested and later germinate in the human gut when conditions are more favorable.
Diagnosis of Food-Borne Illnesses A true assessment of the number of food-borne illnesses may not be realized, as many cases of food-borne illnesses are not diagnosed because the patient does not feel ill enough to seek medical attention. When a person does seek medical attention for symptoms, stool specimens are often evaluated for bacteria and/or parasites. It is important for laboratories to report what organisms they routinely look for in their stool culture work up. Most laboratories routinely look for Shigella, Salmonella, Campylobacter, E. coli O157, and other E. coli Shiga toxin producers, but physician notification may be needed to alert the laboratory to look for Y. enterocolitica or Vibrio species so that appropriate media can be used to optimize the cultivation of those organisms. Special stains, like a modified acid fast-stain, should be ordered when infections with Cyclospora cayetanensis or Cryptosporidium species are suspected. Direct antigen tests for Cryptosporidium may also be used. Blood cultures may be useful for the detection of Brucella species, L. monocytogenes, Vibrio species, or Salmonella species. The recovery of norovirus may require sending fecal specimens to a reference or Public Health Laboratory for reverse transcrip© 2011 Elsevier
tion PCR testing. Toxin testing for botulism, usually performed through a state’s public health laboratory, requires stool and serum. Serology may be used in the diagnosis of brucellosis and trichinellosis. During outbreak situations, food products may be tested. Epidemiologists from the state health department or from the CDC determine what food products are to be tested. Cultures of these food products are usually performed by the local or state public health laboratory.
Preventive Measures Preventive measures, like the pasteurization of milk and dairy products, better manufacturing processes for canning, or education about home canning, and attention to clean water have helped reduce the cases of tuberculosis, typhoid fever, and cholera that were once common causes of food-borne illnesses. However, numerous outbreaks of foodborne illnesses still occur despite the implementation of these preventive measures. Where there are less stringent manufacturing guidelines, contaminated food or beverage products are being produced or imported into the U.S. with the potential to cause food-borne illnesses. Food irradiation is a technology that has recently begun to be used to prevent food-borne illnesses. Three food irradiation methods are available to kill organisms in food products (9). Gamma irradiation uses high-energy gamma rays that can penetrate deeply; this allows the treatment of items on a shipping pallet (9). Electron beam irradiation uses beta rays emitted from an electron gun. This method is used to treat foods in thin layers, as it can only penetrate a few centimeters. X-irradiation is the newest technology and combines the principles of gamma and electron beam irradiation (9). Irradiation works by destroying the organism’s DNA and preventing DNA replication. The treated food products do not become radioactive. It should be noted that not all food products can be irradiated without changing the product or resulting in a perceived change in the product. For example, Gulf Coast oysters are irradiated before being shipped outside of the Gulf Coast region, but consumers in the Gulf Coast region will not eat oysters that have been irradiated Clinical Microbiology Newsletter 33:6,2011
because they believe that the oysters taste different. If used, food irradiation could eliminate E. coli in ground beef, Campylobacter in poultry, Listeria in food and dairy products, and Toxoplasma gondii in meat (9). Precautions that consumers can take to reduce the incidence of food-borne illnesses include cooking meat, poultry, and eggs to temperatures that will kill bacteria; refrigerating leftovers promptly and storing foods at recommended temperatures; avoiding cross-contamination of cooked and raw foods; using clean counter tops, slicing boards, or utensils while cooking; and frequently washing hands and/or using gloves when preparing food. It is important to remember that consumers can all help reduce the rate of food-borne illnesses by taking the appropriate steps listed above. Food-borne illnesses will affect each of us at some point in our lives. We now understand that most food and beverage
Clinical Microbiology Newsletter 33:6,2011
products are capable of serving as a vector for the organisms that can cause illness, whether that is a minor inconvenience or a life-threatening illness. We have seen organisms like C. cayetanensis, a previously unknown coccidian, emerge as food-borne pathogens. Molecular techniques have made it easier to diagnose when viruses like norovirus cause food-borne illnesses. As clinical laboratory scientists, we can aid in recognition of food-borne outbreaks by reporting food-borne pathogens to our local or state health departments and by monitoring trends of these organisms in our clinical settings. In addition, we can aid in education about proper measures to prevent the transmission of these organisms to the public. References 1. Mead, P.S. et al. 1999. Food-related illness and death in the United States. Emerg. Infect. Dis. 5:607-625. 2. http://www.who.int/mediacentre/
© 2011 Elsevier
factsheets/fs237/en/ 3. Murray, P.R. et al. (ed.). Manual of clinical microbiology, 9th ed. ASM Press, Washington, DC. 4. Jones, T.F. 2007. Investigation of foodborne and waterborne disease outbreaks, p. 152-172. In P.R. Murray et al. (ed.). Manual of clinical microbiology, 9th ed. ASM Press, Washington, DC. 5. http://www.cdc.gov/outbreaknet/ foodborne_az.html 6. Centers for Disease Control and Prevention. 2004. Diagnosis and management of foodborne illnesses: a primer for physicians and other healthcare professionals. MMWR Morb. Mortal. Wkly. Rep. 53(RR-4):1-33. 7. http://www.fda.gov/Safety/Recalls/ default.htm 8. http://www.dshs.state.tx.us/news/ releases/20101020.shtm 9. Tauxe, R.V. 2001. Food safety and irradiation: protecting the public from foodborne infections. Emerg. Infect. Dis. 7:516-521.
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www.cmnewsletter.com
$99 March 15, 2011
Food-Borne Illnesses Andrea J. Linscott, Ph.D., D(ABMM), Ochsner Medical Center, Department of Pathology, New Orleans, Louisiana
Abstract Millions of cases of food-borne illnesses occur annually in the United States. These food-borne illnesses can range from mild aggravations to life-threatening situations. Clinical microbiology laboratories play an important part in the detection of these illnesses by identifying and reporting the infections to public health officials, who use the data to detect food-borne outbreaks. This article highlights the more common causes of food-borne illness, symptoms, diagnosis, and prevention. The Centers for Disease Control and Prevention (CDC) estimates that 76 million cases of food-borne illnesses occur annually in the United States (1). The case numbers are based on reportable diseases that each laboratory is required to report to their local or state public health office and by active surveillance conducted by the CDC. Food-borne illnesses can be caused by a variety of substances. As microbiologists, we clearly associate food-borne illnesses with the consumption of contaminated food or beverages that contain bacteria, viruses, or parasites. However, there are non-infectious causes of foodborne illnesses, like chemicals and toxins, that occur as well (2). The majority of food-borne illnesses have either a bacterial or viral etiology. A list of the more common causative agents can be found in Table 1 (3-5). Symptoms of food-borne illnesses may include nausea, vomiting, and diarrhea, which typically last for 2 to 3 days in most individuals. However, severe complications can occur from food-borne illnesses in certain patients. These Corresponding Author: Andrea J. Linscott, Ph.D., D(ABMM), Ochsner Medical Center, Department of Pathology, 1514 Jefferson Highway, New Orleans, LA 70121. Tel.: 504-842-2171. Fax: 504-842-3515. E-mail: [email protected]
Clinical Microbiology Newsletter 33:6,2011
severe complications may include stillbirths, hospitalization due to sepsis, hemolytic uremic syndrome, Reiter’s syndrome (reactive arthritis), GuillanBarré syndrome (nerve paralysis), and/ or death. Table 1 also illustrates that severe complications are often associated with certain patient populations such as the very young or older patients or patients with underlying conditions and infections with certain organisms. Some examples of organism/complication correlations are Listeria – stillbirths, Shiga-toxin producing Escherichia coli (STEC) – hemolytic uremic syndrome, and Vibrio vulnificus sepsis in alcoholic patients. Preliminary data from FoodNet, a collaborative program comprised of 10 state health departments, CDC, the Food and Drug Administration, and the U.S. Department of Agriculture’s Food Safety and Inspection Service, listed the most common pathogens for food-borne illnesses for 2009, from highest to lowest incidence, as Salmonella, Campylobacter, Shigella, Cryptosporidium, STEC O157, STEC non-O157, Vibrio, Listeria, Yersina, and Cyclospora (6). Compared to previous years, there has been an increased incidence of Vibrio, while there has been a decrease in Shigella and STEC O157. These data also show that children less than 4 years © 2011 Elsevier
of age have the highest reported incidence of food-borne illnesses; however, adults 50 years of age have the highest hospitalization and fatality rates (6). The organisms that were most responsible for hospitalization of adults, in descending order, are STEC O157, Salmonella, Yersinia, Vibrio, STEC non-O157, Shigella, Cyclospora, Cryptosporidium, and Campylobacter. Listeria had the highest fatality rate in adults over 50, followed by Vibrio (6). Food-borne outbreaks are defined by the CDC as the “occurrence of two or more similar illnesses resulting from the ingestion of a common food.” When food products have been identified as a causative agent in a food-borne outbreak or if quality control measures during food processing indicate potential contamination, the food or beverage product may be recalled. A review of information from the U.S. Food and Drug
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41
Table 1. Common causative agents of food-borne illnesses Incubation period
Organism
Signs and symptoms
Epidemiology
Laboratory diagnosis
Bacillus cereus – preformed enterotoxin, emetic type
1 to 6 h
Sudden onset of nausea and vomiting, with or without diarrhea
Cooked foods, like meat or fried rice, that have not been properly refrigerated
Usually not performed; stool and food sources may be needed for public health investigation.
Bacillus cereus – diarrheal type
8 to 16 h
Abdominal pain with diarrhea
Variety of foods from meat, vegetables, pasta, deserts, cakes, sauces, milk
Usually not performed; stool and food sources may be needed for public health investigation.
Brucella sp.
7 to 21 days
Fever, night sweats, backache, muscle aches, diarrhea
Raw milk or other unpasteurized dairy products, meat
Positive serology and/or blood culture(s)
Campylobacter jejuni
2 to 5 days
Fever, abdominal cramping, diarrhea with or without blood; Guillan-Barre syndrome can be seen in some individuals.
Raw and undercooked poultry, unpasteurized milk, contaminated water
Stool culture with specific medium, temperature, and atmospheric conditions; rapid immuno-chromogenic tests or molecular assays
Clostridium botulinum – preformed toxin
12 to 72 h
Abdominal cramping, nausea, vomiting, diarrhea, double vision; death or long term nerve damage may be seen.
Improperly canned foods, herb-infused oils, baked potatoes in aluminum foil
Toxin testing of serum, stool, and/or food performed at some state health department laboratories or CDC
Clostridium botulinum – infant
3 to 30 days
Floppy baby syndrome – lethargy, weakness, poor head control; constipation, poor feeding and sucking reflexes
Honey, home-canned vegetables and fruits, corn syrup
Toxin testing of serum, stool, and/or food performed at some state health department laboratories or CDC
Clostridium perfringens – toxin
8 to 16 h
Diarrhea, abdominal cramping, and nausea
Meat, poultry, gravy, inadequately reheated food
Test stool for enterotoxin; not routinely performed in most clinical laboratories
Cryptosporidium sp.
2 to 10 days
Watery diarrhea, abdominal cramps; severity depends on host immune status.
Undercooked food or food contaminated by ill food handler, contaminated drinking water
Detection of oocysts in stool using modified acid-fast stain, direct fluorescent antibodies, or with immunoassays
Cyclospora cayetanensis
1 to 14 days
Watery diarrhea, abdominal pain, nausea, loss of appetite, and weight loss
Fresh fruits and vegetables
Detection of oocysts in stool using modified acid-fast stain
Enterohemorrhagic E. coli – O157:H7 and other Shiga toxins
1 to 8 days
Bloody diarrhea, abdominal pain and vomiting; fever may be absent; hemolytic uremic syndrome.
Undercooked beef, unpasteurized milk and fruit juices, raw fruits, and vegetables
Isolation of the organism from stool culture using Sorbitol MacConkey or CHROMagar media; confirmation using antisera or latex agglutination; detection of the shiga toxins by immunoassay testing
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© 2011 Elsevier
Clinical Microbiology Newsletter 33:6,2011
Table 1. Common causative agents of food-borne illnesses (continued) Organism
Incubation period
Signs and symptoms
Epidemiology
Laboratory diagnosis
Hepatitis A virus
15 to 50 days
Diarrhea, jaundice, dark urine, fever, headache, nausea, and abdominal pain
Raw product, contaminated drinking water, food contaminated by infected food handlers, and shellfish from contaminated water
Increase in ALT and bilirubin; serology test: positive IgM and anti-hepatits A antibodies
Listeria monocytogenes
9 to 48 h (gastrointestinal) 2 to 6 wk (invasive disease)
Diarrhea, fever, muscle ache, and nausea; pregnant women may have mild flu-like symptoms, and infection may lead to premature delivery or stillbirth. Meningitis and sepsis may be seen in elderly or immunocompromised individuals.
Unpasteurized milk, soft cheese made with unpasteurized milk, ready-to-eat deli meats and hot dogs
Blood and cerebrospinal fluid cultures; antibodies to listerolysin O; stool culture may not be useful, as asymptomatic carriage does occur.
Noroviruses
12 to 48 h
Nausea, vomiting, diarrhea, abdominal pain, fever, and headache
Raw produce, contaminated drinking water, food contaminated by infected food handler, shellfish from contaminated water
Reverse transcription PCR performed on fresh, unpreserved stool samples; negative stool cultures and fecal stain for white blood cells
Salmonella spp.
1 to 3 days (non-Typhi) 3 to 60 days (Typhi)
Non-Typhi: diarrhea, fever and abdominal cramps Typhi: Fever, chills, anorexia, malaise, constipation, and myalgia
Contaminated eggs; poultry; unpasteurized milk, dairy products, or juice; contaminated raw fruits and vegetables
Stool cultures (non-Typhi) Stool and blood cultures (Typhi)
Shigella spp.
24 to 48 h
Diarrhea (+/- blood and mucus), fever, and abdominal cramps
Food or water contaminated by fecal material; food contaminated by infected person
Stool culture
Staphylococcus aureus (preformed enterotoxin)
1 to 6 h
Sudden onset of nausea and vomiting and abdominal cramps; fever and diarrhea may be present.
Unrefrigerated or improperly refrigerated meats, potato and egg salads, or cream pastries
Clinical diagnosis; toxin can be tested from stool, vomitus, or food through public laboratory or reference laboratory.
Trichinella spiralis
1 to 2 days for intestinal symptoms; 2 to 4 wk for systemic symptoms
Acute phase: nausea, diarrhea, vomiting, fatigue, abdominal pain. Systemic phase: muscle soreness, periorbital edema, eosinophilia, occasional cardiac and neurologic abnormalities
Raw or undercooked contaminated meat (pork, bear, walrus, moose), crosscontaminated ground beef, lamb
Positive serology, demonstration of larvae in muscle biopsy specimens, increase in eosinophils
Vibrio cholerae (O1, O139) (non-O1 or non-O139)
24 to 72 h
Profuse watery diarrhea, vomiting; dehydration and death can occur within several hours.
Contaminated water, raw fish, shellfish, and crustaceans
Stool culture, including thiosulfate citrate bile salts sucrose agar (request needed to include specific media)
Vibrio parahaemolyticus
2 to 48 h
Watery diarrhea, abdominal cramps, nausea, vomiting
Raw or undercooked seafood or cooked seafood contaminated with seawater
Stool culture, including thiosulfate citrate bile salts sucrose agar (request needed to include specific media)
Vibrio vulnificus
1 to 7 days
Vomiting, diarrhea, abdominal pain, possible sepsis (especially in alcoholic patients or patients with liver problems)
Raw or undercooked seafood or cooked seafood contaminated with seawater
Stool culture, including thiosulfate citrate bile salts sucrose agar (request needed to include specific media)
Yersinia enterocolitica
24 to 48 h
Diarrhea, vomiting, fever, abdominal pain (may mimic appendicitis)
Undercooked pork, unpasteurized milk, tofu, contaminated water, chitterlings
Stool or blood cultures, including cefsulodin-irgasannovobiocin agar or routine stool media held at appropriate temperature
Clinical Microbiology Newsletter 33:6,2011
© 2011 Elsevier
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Administration Safety Recall website shows that for 2010, were been over 100 recalls due to “possible health risks” (7). Salmonella was the organism most commonly linked with food product recalls. In 2010, over 550 million eggs were recalled due to possible Salmonella contamination, resulting in one of the largest massive recalls (7). Other products recalled due to potential Salmonella contamination were headcheese, pickles, salami, raw tuna, frozen dinners, alfalfa sprouts, lettuce, tomatoes, and olives (7). Interestingly, there have been numerous recalls of pet food and pet treat products for Salmonella contamination (7). Pet food contamination is not usually a problem for the family pet but for the human who is handling the food product or treat and then not adequately washing their hands afterwards. A typhoid outbreak was associated with mamey pulp used in frozen drinks. In October 2010, there was a Listeria monocytogenes outbreak related to celery contamination in a processing plant, and at the time of this writing, 5 people had died from that outbreak (8). Numerous recalls of beef have been linked to E. coli O157:H7 contamination. In addition, buffalo meat and fruit compote have been linked to E. coli O157 outbreaks (7). An outbreak in a hospital cafeteria, in which one person died, was related to chicken salad contaminated with Clostridium perfringens (7). Norovirus was responsible for an outbreak at an Ivy League faculty club, as well as at the 2010 American Society for Microbiology Annual meeting (7). I can personally attest to the ASM outbreak, as I was one of the participants who became ill.
Epidemiology of Contaminated Food Food can become contaminated in several different ways. The source of the organism can be a healthy animal’s gastrointestinal tract, and those organisms may contaminate the animal carcass during slaughter. If that contaminated carcass is not thoroughly cooked, the organisms can be transmitted to humans. Examples of this type of transmission are Salmonella and Campylobacter found in chicken or E. coli O157 found in beef that has not been adequately cooked. Contamination of fruits and vegetables can occur when 44
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water contaminated with human or animal fecal material is used to irrigate the produce. Food handlers can spread organisms such as Shigella, hepatitis A virus, or norovirus via the fecal-oral route or when they have skin lesions caused by an organism like Staphylococcus aureus. Improperly cleaned cooking utensils and/or contaminated kitchen counters can aid in the transmission of these organisms that cause food-borne illness. During certain times of the year, shellfish and oysters harbor higher numbers of Vibrio species than normal, and eating them should be avoided during these times. Organisms like L. monocytogenes and Yersinia enterocolitica can actively multiply in foods, like deli meats and unpasteurized milk products, stored at refrigerated temperatures. Clostridium species and Bacillus cereus can produce toxins in food kept at inadequate temperatures or produce spores that are ingested and later germinate in the human gut when conditions are more favorable.
Diagnosis of Food-Borne Illnesses A true assessment of the number of food-borne illnesses may not be realized, as many cases of food-borne illnesses are not diagnosed because the patient does not feel ill enough to seek medical attention. When a person does seek medical attention for symptoms, stool specimens are often evaluated for bacteria and/or parasites. It is important for laboratories to report what organisms they routinely look for in their stool culture work up. Most laboratories routinely look for Shigella, Salmonella, Campylobacter, E. coli O157, and other E. coli Shiga toxin producers, but physician notification may be needed to alert the laboratory to look for Y. enterocolitica or Vibrio species so that appropriate media can be used to optimize the cultivation of those organisms. Special stains, like a modified acid fast-stain, should be ordered when infections with Cyclospora cayetanensis or Cryptosporidium species are suspected. Direct antigen tests for Cryptosporidium may also be used. Blood cultures may be useful for the detection of Brucella species, L. monocytogenes, Vibrio species, or Salmonella species. The recovery of norovirus may require sending fecal specimens to a reference or Public Health Laboratory for reverse transcrip© 2011 Elsevier
tion PCR testing. Toxin testing for botulism, usually performed through a state’s public health laboratory, requires stool and serum. Serology may be used in the diagnosis of brucellosis and trichinellosis. During outbreak situations, food products may be tested. Epidemiologists from the state health department or from the CDC determine what food products are to be tested. Cultures of these food products are usually performed by the local or state public health laboratory.
Preventive Measures Preventive measures, like the pasteurization of milk and dairy products, better manufacturing processes for canning, or education about home canning, and attention to clean water have helped reduce the cases of tuberculosis, typhoid fever, and cholera that were once common causes of food-borne illnesses. However, numerous outbreaks of foodborne illnesses still occur despite the implementation of these preventive measures. Where there are less stringent manufacturing guidelines, contaminated food or beverage products are being produced or imported into the U.S. with the potential to cause food-borne illnesses. Food irradiation is a technology that has recently begun to be used to prevent food-borne illnesses. Three food irradiation methods are available to kill organisms in food products (9). Gamma irradiation uses high-energy gamma rays that can penetrate deeply; this allows the treatment of items on a shipping pallet (9). Electron beam irradiation uses beta rays emitted from an electron gun. This method is used to treat foods in thin layers, as it can only penetrate a few centimeters. X-irradiation is the newest technology and combines the principles of gamma and electron beam irradiation (9). Irradiation works by destroying the organism’s DNA and preventing DNA replication. The treated food products do not become radioactive. It should be noted that not all food products can be irradiated without changing the product or resulting in a perceived change in the product. For example, Gulf Coast oysters are irradiated before being shipped outside of the Gulf Coast region, but consumers in the Gulf Coast region will not eat oysters that have been irradiated Clinical Microbiology Newsletter 33:6,2011
because they believe that the oysters taste different. If used, food irradiation could eliminate E. coli in ground beef, Campylobacter in poultry, Listeria in food and dairy products, and Toxoplasma gondii in meat (9). Precautions that consumers can take to reduce the incidence of food-borne illnesses include cooking meat, poultry, and eggs to temperatures that will kill bacteria; refrigerating leftovers promptly and storing foods at recommended temperatures; avoiding cross-contamination of cooked and raw foods; using clean counter tops, slicing boards, or utensils while cooking; and frequently washing hands and/or using gloves when preparing food. It is important to remember that consumers can all help reduce the rate of food-borne illnesses by taking the appropriate steps listed above. Food-borne illnesses will affect each of us at some point in our lives. We now understand that most food and beverage
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products are capable of serving as a vector for the organisms that can cause illness, whether that is a minor inconvenience or a life-threatening illness. We have seen organisms like C. cayetanensis, a previously unknown coccidian, emerge as food-borne pathogens. Molecular techniques have made it easier to diagnose when viruses like norovirus cause food-borne illnesses. As clinical laboratory scientists, we can aid in recognition of food-borne outbreaks by reporting food-borne pathogens to our local or state health departments and by monitoring trends of these organisms in our clinical settings. In addition, we can aid in education about proper measures to prevent the transmission of these organisms to the public. References 1. Mead, P.S. et al. 1999. Food-related illness and death in the United States. Emerg. Infect. Dis. 5:607-625. 2. http://www.who.int/mediacentre/
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factsheets/fs237/en/ 3. Murray, P.R. et al. (ed.). Manual of clinical microbiology, 9th ed. ASM Press, Washington, DC. 4. Jones, T.F. 2007. Investigation of foodborne and waterborne disease outbreaks, p. 152-172. In P.R. Murray et al. (ed.). Manual of clinical microbiology, 9th ed. ASM Press, Washington, DC. 5. http://www.cdc.gov/outbreaknet/ foodborne_az.html 6. Centers for Disease Control and Prevention. 2004. Diagnosis and management of foodborne illnesses: a primer for physicians and other healthcare professionals. MMWR Morb. Mortal. Wkly. Rep. 53(RR-4):1-33. 7. http://www.fda.gov/Safety/Recalls/ default.htm 8. http://www.dshs.state.tx.us/news/ releases/20101020.shtm 9. Tauxe, R.V. 2001. Food safety and irradiation: protecting the public from foodborne infections. Emerg. Infect. Dis. 7:516-521.
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