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Appendix B
Guidelines for Confirmation of Foodborne-Disease Outbreaks

A foodborne-disease outbreak (FBDO) is defined as an incident in which two or more persons experience a similar illness resulting from the ingestion of a common food.* The following table provides information about incubation periods, clinical syndromes, and criteria for confirming the etiology once an FBDO has been identified. The information on incubation periods and clinical syndromes is provided as a guideline and should not be included in the confirmation criteria. These guidelines might not include all etiologic agents and diagnostic tests.

FBDOs should be reported to the Foodborne and Diarrheal Diseases Branch at CDC on Form 52.13, Investigation of a Foodborne Outbreak, which was updated in October 1999. Provision of other documents describing the outbreak investigation also is encouraged. For information regarding collection of laboratory specimens and for additional information on viral agents, refer to other CDC publications (i.e., "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]).

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



Table B

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Table B. Guidelines for confirmation of foodborne-disease outbreaks

Etiologic agent Incubation period Clinical syndrome Confirmation
Bacterial      
       
1. Bacillus cereus      
  a. 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
  b. 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
       
2. 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
       
3. 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
       
4. Clostridiumbotulinum 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 botulinal toxin in serum, stool, gastric contents, or implicated food
      OR
      Isolation or organism from stool or intestine
       
5. Clostridium perfringens 6-24 hrs Diarrhea, abdominal cramps; vomiting and fever uncommon Isolation of 105 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
       
6. Escherichia coli      
  a. 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
  b. 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
  c. Enteropathogenic (EPEC) Variable Diarrhea, fever, abdominal cramps Isolation of organism of same enteropathogenic serotype from stool of two or more ill persons
  d. Enteroinvasive (EIEC) Variable Diarrhea (might be bloody), fever, abdominal cramps Isolation of same enteroinvasive serotype from stool of two or more ill persons
       
7. Listeria monocytogenes      
  a. Invasive disease 2-6 wks Meningitis, neonatal sepsis, fever Isolation of organism from normally sterile site
  b. 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
       
8. 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
       
9. 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
       
10. Shigella spp. 12 hrs-6 days; usually 2-4 days Diarrhea (often bloody), often accompanied by 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
       
11. 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
       
12. 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
       
13. Vibrio cholerae      
  a. 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
  b. non-O1 and non-O139 1-5 days Watery diarrhea Isolation of organism of same serotype from stool of two or more ill persons
       
14. 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
15. 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
       
Chemical      
       
1. Marine toxins      
  a. 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)
  b. 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)
  c. Paralytic or neurotoxic shellfish 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
  d. 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
       
2. Heavy metals 5 min-8 hrs; usually <1 hr Vomiting, often metallic taste Demonstration of high concentration of metal in epidemiologically implicated food
  • Antimony 
  • Cadmium
  • Copper
  • Iron
  • Tin
  • Zinc
      
       
3. 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)
       
4. Mushroom toxins      
  a. Shorter-acting toxins 2 hrs Usually vomiting and diarrhea, other symptoms differ with toxin Clinical syndrome among persons who have eaten mushroom identified as toxic type
  • Muscimol
  • Muscarine
  • Psilocybin
  • Coprinus artrementaris
  • Ibotenic acid
  
  • Confusion, visual disturbance
  • Salivation, diaphoresis
  • Hallucinations
  • Disulfiram-like reaction
  • Confusion, visual disturbance
 OR
      Demonstration of toxin in epidemiologically implicated mushroom or food containing mushroom
b. Longer-acting toxins (e.g., Amanitaspp.) 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
       
Parasitic      
       
1. Cryptosporidium parvum 2-28 days; median: 7 days Diarrhea, nausea, vomiting; fever Demonstration of organism or antigen in stool or in small-bowel biopsy of two or more ill persons
      OR
      Demonstration of toxin in epidemiologically implicated food
       
2. Cyclospora cayetanensus 1-11 days; median: 7 days Fatigue, protracted diarrhea, often relapsing Demonstration of organism in stool of two or more ill persons
       
3. Giardia lamblia 3-25 days; median: 7 days Diarrhea, gas, cramps, nausea, fatigue Two or more ill persons and detection of antigen in stool or demonstration of organism in stool, duodenal contents, or small-bowel biopsy specimen
       
4. Trichinellaspp. 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
       
Viral      
       
1. Hepatitis A 15-50 days; median: 28 days Jaundice, dark urine, fatigue, anorexia, nausea Detection of immunoglobulin M anti-hepatitis A virus in serum from two or more persons who consumed epidemiologically implicated food
       
2. Norwalk family of viruses, small round-structured viruses (SRSV) 15-77 hrs; usually 24-48 hrs Vomiting, cramps, diarrhea, headache More than fourfold rise in antibody titer to Norwalk virus or Norwalk-like virus in acute and convalescent sera in most serum pairs
      OR
      Visualization of small, round-structured viruses that react with patient’s convalescent sera but not acute sera — by immune-electron microsopy (assays based on molecular diagnostics [e. g., polymerase-chain reaction, probes, or assays for antigen and antibodies from expressed antigen] are available in reference laboratories)
       
3. Astrovirus, calicivirus, others 15-77 hrs; usually 24-48 hrs Vomiting, cramps, diarrhea, headache Visualization of small, round-structured viruses that react with patient’s convalescent sera but not acute sera — by immune-electron microsopy (assays based on molecular diagnostics [e. g., polymerase-chain reaction, probes, or assays for antigen and antibodies from expressed antigen] are available in reference laboratories)

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