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Guide to Confirming an Etiology in Foodborne Disease Outbreak

Report a Foodborne Disease Outbreak

A foodborne disease outbreak is defined as an incident in which two or more persons experience a similar illness resulting from the ingestion of a common food.* Foodborne disease outbreaks should be reported to CDC’s Enteric Diseases Epidemiology Branch through the National Outbreak Reporting System (NORS).**

The following tables provide information about etiologic agents (causes), incubation periods, clinical syndromes, and criteria for confirmation of a case after a foodborne disease outbreak has been identified. The information on incubation periods and clinical syndromes is not part of confirmation criteria. These guidelines might not include all etiologic agents and diagnostic tests.

Guidelines for Confirming Cause of Foodborne Disease Outbreaks

Etiologic Agent Incubation Period Clinical Syndrome Confirmation

Bacillus cereus - Vomiting toxin

1-6 hrs

Vomiting; some patients with diarrhea; fever uncommon

Isolation of organism from stool of two or more ill persons and not from stool of control patients

OR

Isolation of 105 organisms/g from epidemiologically implicated food, provided specimen is properly handled

Bacillus cereus - Diarrheal toxin

6-24 hrs

Diarrhea, abdominal cramps, and vomiting in some patients; fever uncommon

Isolation of organism from stool of two or more ill persons and not from stool of control patients

OR

Isolation of 105 organisms/g from epidemiologically implicated food, provided specimen is properly handled

Brucella

Several days to several mos; usually >30 days

Weakness, fever, headache, sweats, chills, arthralgia, weight loss, splenomegaly

Two or more ill persons and isolation of organism in culture of blood or bone marrow; greater than fourfold increase in standard agglutination titer (SAT) over several wks, or single SAT 1:160 in person who has compatible clinical symptoms and history of exposure

Campylobacter jejuni/coli

2-10 days; usually 2-5 days

Diarrhea (often bloody), abdominal pain, fever

Isolation of organism from clinical specimens from two or more ill persons

OR

Isolation of organism from epidemiologically implicated food

Clostridium botulinum

2 hrs-8 days; usually 12-48 hrs

Illness of variable severity; common symptoms are diplopia, blurred vision, and bulbar weakness; paralysis, which is usually descending and bilateral, might progress rapidly

Detection of botulinum toxin in serum, stool, gastric contents, or implicated food

OR

Isolation of organism from stool or intestine

Clostridium perfringens

6-24 hrs

Diarrhea, abdominal cramps; vomiting and fever uncommon

Isolation of 106 organisms/g from stool of two or more ill persons, provided specimen is properly handled.

OR

Demonstration of enterotoxin in the stool of two or more ill persons

OR

Isolation of 105 organisms/g from epidemiologically implicated food, provided specimen is properly handled

Escherichia coli - Enterohemorrhagic (E. coli O157:H7 and others)

1-10 days; usually 3-4 days

Diarrhea (often bloody), abdominal cramps (often severe), little or no fever

Isolation of E. coli O157:H7 or other Shiga-like toxin-producing E. coli from clinical specimen from two or more ill persons

OR

Isolation of E. coli O157:H7 or other Shiga-like toxin-producing E. coli from epidemiologically implicated food

Escherichia coli - Enterotoxigenic (ETEC)

6-48 hrs

Diarrhea, abdominal cramps, nausea; vomiting and fever less common

Isolation of organism of same serotype, demonstrated to produce heat-stable (ST) and/or heat-labile (LT) enterotoxin, from stool of two or more ill persons

Escherichia coli - Enteropathogenic (EPEC)

Variable

Diarrhea, fever, abdominal cramps

Isolation of organism of same enteropathogenic serotype from stool of two or more ill persons

Escherichia coli - Enteroinvasive (EIEC)

Variable

Diarrhea (might be bloody), fever, abdominal cramps

Isolation of same enteroinvasive serotype from stool of two or more ill persons

Listeria monocytogenes - Invasive disease

2-6 wks

Meningitis, neonatal sepsis, fever

Isolation of organism from normally sterile site

Listeria monocytogenes - Diarrheal disease

Unknown

Diarrhea, abdominal cramps, fever

Isolation of organism of same serotype from stool of two or more ill persons exposed to food that is epidemiologically implicated or from which organism of same serotype has been isolated

Nontyphoidal Salmonella

6 hrs-10 days; usually 6-48 hrs

Diarrhea, often with fever and abdominal cramps

Isolation of organism of same serotype from clinical specimens from two or more ill persons

OR

Isolation of organism from epidemiologically implicated food

Salmonella Typhi

3-60 days; usually 7-14 days

Fever, anorexia, malaise, headache, and myalgia; sometimes diarrhea or constipation

Isolation of organism from clinical specimens from two or more ill persons

OR

Isolation of organism from epidemiologically implicated food

Shigella spp.

12 hrs-6 days; usually 2-4 days

Diarrhea (sometimes bloody), often accompanied by fever and abdominal cramps

Isolation of organism of same species or serotype from clinical specimens from two or more ill persons

OR

Isolation of organism from epidemiologically implicated food

Staphylococcus aureus

30 min-8 hrs; usually 2-4 hrs

Vomiting, diarrhea

Isolation of organism of same phage type from stool or vomitus of two or more ill persons

OR

Detection of enterotoxin in epidemiologically implicated food

OR

Isolation of 105 organisms/g from epidemiologically implicated food, provided specimen is properly handled

Streptococcus, group A

1-4 days

Fever, pharyngitis, scarlet fever, upper respiratory infection

Isolation of organism of same M- or T-type from throats of two or more ill persons

OR

Isolation of organism of same M- or T-type from epidemiologically implicated food

Vibrio cholerae - O1 or O139

1-5 days

Watery diarrhea, often accompanied by vomiting

Isolation of toxigenic organism from stool or vomitus of two or more ill persons

OR

Significant rise in vibriocidal, bacterial-agglutinating, or antitoxin antibodies in acute- and early convalescent-phase sera among persons not recently immunized

OR

Isolation of toxigenic organism from epidemiologically implicated food

Vibrio cholerae - non-O1 and non-O139

1-5 days

Watery diarrhea

Isolation of organism of same serotype from stool of two or more ill persons

Vibrio parahaemolyticus

4-30 hrs

Diarrhea

Isolation of Kanagawa-positive organism from stool of two or more ill persons

OR

Isolation of 105 Kanagawa-positive organisms/g from epidemiologically implicated food, provided specimen is properly handled

Yersinia enterocolitica

1-10 days; usually 4-6 days

Diarrhea, abdominal pain (often severe)

Isolation of organism from clinical specimen from two or more ill persons

OR

Isolation of pathogenic strain of organism from epidemiologically implicated food

Etiologic Agent Incubation Period Clinical Syndrome Confirmation

Marine toxins - Ciguatoxin

1-48 hrs; usually 2-8 hrs

Usually gastrointestinal symptoms followed by neurologic symptoms(including paresthesia of lips, tongue, throat, or extremities) and reversal of hot and cold sensation

Demonstration of ciguatoxin in epidemiologically implicated fish

OR

Clinical syndrome among persons who have eaten a type of fish previously associated with ciguatera fish poisoning (e.g., snapper, grouper, or barracuda)

Marine toxins - Scombroid toxin (histamine)

1 min-3 hrs; usually 1 hr

Flushing, dizziness, burning of mouth and throat, headache, gastrointestinal symptoms, urticaria, and generalized pruritis

Demonstration of histamine in epidemiologically implicated fish

OR

Clinical syndrome among persons who have eaten a type of fish previously associated with histamine fish poisoning (e.g., mahi-mahi or fish of order Scomboidei)

Marine toxins - Paralytic or neurotoxic shellfish poison

30 min-3 hrs

Paresthesia of lips, mouth or face, and extremities; intestinal symptoms or weakness, including respiratory difficulty

Detection of toxin in epidemiologically implicated food

OR

Detection of large numbers of shellfish-poisoning-associated species of dinoflagellates in water from which epidemiologically implicated mollusks are gathered

Marine toxins - Puffer fish, tetrodotoxin

10 min-3 hrs; usually 10-45 min

Paresthesia of lips, tongue, face, or extremities, often following numbness; loss of proprioception or floating sensations

Demonstration of tetrodotoxin in epidemiologically implicated fish

OR

Clinical syndrome among persons who have eaten puffer fish

Heavy metals (Antimony, Cadmium, Copper, Iron, Tin, Zinc)

5 min-8 hrs; usually <1 hr

Vomiting, often metallic taste

Demonstration of high concentration of metal in epidemiologically implicated food

Monosodium glutamate (MSG)

3 min-2 hrs; usually <1 hr

Burning sensation in chest, neck, abdomen, or extremities; sensation of lightness and pressure over face or heavy feeling in chest

Clinical syndrome among persons who have eaten food containing MSG (e.g., usually 1.5 g MSG)

Mushroom toxins - Shorter-acting toxins (Muscimol, Muscarine, Psilocybin, Coprinus artrementaris, Ibotenic acid)

2 hrs

Usually vomiting and diarrhea, other symptoms differ with toxin

  • Confusion, visual disturbance

  • Salivation, diaphoresis

  • Hallucinations

  • Disulfiram-like reaction

  • Confusion, visual disturbance

Clinical syndrome among persons who have eaten mushroom identified as toxic type

OR

Demonstration of toxin in epidemiologically implicated mushroom or food containing mushroom

Mushroom toxins - Longer-acting toxins (e.g., Amanita spp.)

6-24 hrs

Diarrhea and abdominal cramps for 24 hrs followed by hepatic and renal failure

Clinical syndrome among persons who have eaten mushroom identified as toxic type

OR

Demonstration of toxin in epidemiologically implicated mushroom or food containing mushrooms

Etiologic Agent Incubation Period Clinical Syndrome Confirmation

Cryptosporidium spp.

2-28 days; median: 7 days

Diarrhea, nausea, vomiting; fever

Demonstration of oocysts in stool or in small-bowel biopsy of two or more ill persons

OR

Demonstration of organism in epidemiologically implicated food

Cyclospora cayetanensis

1-14 days; median: 7 days

Diarrhea, nausea, anorexia, weight loss, cramps, gas, fatigue, low-grade fever; may be relapsing or protracted

Demonstration of the parasite by microscopy or molecular methods in stool or in intestinal aspirate or biopsy specimens from two or more ill persons

OR

Demonstration of the parasite in epidemiologically implicated food

Giardia intestinalis

3-25 days; median: 7 days

Diarrhea, gas, cramps, nausea, fatigue

Demonstration of the parasite in stool or small-bowel biopsy specimen of two or more ill persons

Trichinella spp.

1-2 days for intestinal phase; 2-4 wks for systemic phase

Fever, myalgia, periorbital edema, high eosinophil count

Two or more ill persons and positive serologic test or demonstration of larvae in muscle biopsy

OR

Demonstration of larvae in epidemiologically implicated meat

Etiologic Agent Incubation Period Clinical Syndrome Confirmation

Hepatitis A

15-50 days; median: 28 days

Jaundice, dark urine, fatigue, anorexia, nausea

Detection of immunoglobulin M antibody to hepatitis A virus (IgM anti-HAV) in serum from two or more persons who consumed epidemiologically implicated food

Norovirus (NoV)

12-48 hrs (median 33 hours)

Diarrhea, vomiting, nausea, abdominal cramps, low-grade fever

Detection of viral RNA in at least two bulk stool or vomitus specimens by real-time or conventional reverse transcriptase-polymerase chain reaction (RT-PCR)

OR

Visualization of viruses (NoV) with characteristic morphology by electron microscopy in at least two or more bulk stool or vomitus specimens

OR

Two or more stools positive by commercial enzyme immunoassay (EIA)

Astrovirus

12-48 hrs

Diarrhea, vomiting, nausea, abdominal cramps, low-grade fever

Detection of viral RNA in at least two bulk stool or vomitus specimens by real-time or conventional reverse transcriptase-polymerase chain reaction (RT-PCR)

OR

Visualization of viruses (NoV) with characteristic morphology by electron microscopy in at least two or more bulk stool or vomitus specimens

OR

Two or more stools positive by commercial enzyme immunoassay (EIA)

* Before 1992, three exceptions existed to this definition; only one case of botulism, marine-toxin intoxication, or chemical intoxication was required to constitute a foodborne disease outbreak if the etiology was confirmed. The definition was changed in 1992 to require two or more cases to constitute an outbreak.

** For information regarding the general criteria and confirmation tests used by the national Foodborne Disease Outbreak Surveillance System, refer to Centers for Disease Control and Prevention (CDC). Surveillance for Foodborne Disease Outbreaks, United States, 2013, Annual Report. Atlanta, Georgia: US Department of Health and Human Services, CDC, 2015. For information regarding the collection of laboratory specimens and for additional information on viral agents, refer to "Recommendations for Collection of Laboratory Specimens Associated with Outbreaks of Gastroenteritis," MMWR 1990:39[No. RR-14] and "Viral Agents of Gastroenteritis: Public Health Importance and Outbreak Management," MMWR 1990;39[No. RR-5]).

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