Foodborne Illness Primer for Physicians and Other Healthcare Professionals: A Review

Olugbenga Obasanjo, MD, MPH, PhD


August 10, 2010


In 2001, a foodborne illness primer for physicians and other healthcare professionals was prepared by the Foodborne Illness Primer Work Group. This group consisted of specialists in the field from the American Medical Association, the American Nurses Association, the Centers for Food Safety and Applied Nutrition of the US Food and Drug Administration, and the Food Safety and Inspection Service of the US Department of Agriculture. The primer is a guide for primary care and emergency medicine clinicians, who are likely to see the initial case of a potential food-related disease outbreak. It is also intended to serve as a teaching tool to update physicians and other healthcare professionals about foodborne illness and call attention to their important role in recognizing symptoms, disease clusters, and etiologic agents and in reporting cases of foodborne illness to public health authorities.[1] The original complete primer was printed in the January 26, 2001, issue of Morbidity and Mortality Weekly Report (MMWR),[2] with summaries in subsequent issues of MMWR and in other journals. The primer and the updates present case studies of different pathogens and conditions. Even though the primer was originally published before the increased alert following September 11, 2001, its reprints and updates have included considerations of new realities following those tragic events. The primer has been reviewed and cited in several articles that address the issue of foodborne illnesses and is recognized as a useful tool in identifying and managing these conditions.

This article summarizes and briefly discusses key aspects of the primer, with the goal of bringing the salient points to healthcare professionals and elucidating their role in identifying and controlling potential foodborne outbreaks. Throughout this article are recommendations for how physicians and other healthcare professionals can:

  • Recognize the potential for a foodborne cause of a patient's illness;

  • Identify cases of foodborne illness that both have and do not have gastrointestinal tract symptoms;

  • Obtain stool cultures in appropriate settings;

  • Recognize that testing for some specific pathogens (eg, Escherichia coli O157:H7 and Vibrio species) must be requested;

  • Report suspect cases to appropriate public health officials;

  • Talk with patients about ways to prevent food-related diseases; and

  • Be aware that any patient with foodborne illness could represent the first case of a more widespread outbreak.

A foodborne illness is any illness associated with or resulting from ingestion of food. This definition, as in most texts, is intentionally broad to accommodate the diverse methods and agents responsible for foodborne illness. These agents include microorganisms, marine organisms, and fungi, along with their associated toxins, and various chemical contaminants. The organism/agent and the vehicle causing the illness vary, although certain vehicles are known to be commonly associated with certain types of illness. For example, in 2006, norovirus was responsible for 337 (98%) of virus-caused outbreaks identified in the United States, whereas only 17 food commodities were responsible for 6395 (50%) of cases in which a food vehicle was identified.[3] However, in most cases of foodborne illness, people do not seek medical care, and when they do, they are unable or unwilling to give samples that can help identify the cause of the illness. Although viruses are thought to be associated with most foodborne illnesses in the United States, clinical tests for viruses are rarely done. The bacterial agents most often identified in patients with foodborne illness in the United States are Campylobacter, Salmonella, and Shigella species, with substantial variation occurring by geographic area and season.[2]

It is therefore important that healthcare professionals remain current on commonly occurring organisms, vehicles, and symptoms associated with foodborne illness, given that the few cases they see may serve as sentinel signals for more widespread infection. Healthcare professionals also should be aware of unusual presentations, pathogens, and vehicles, especially against the backdrop of potential intentional contamination and adulteration. Healthcare professionals also should be aware of the effects of global commerce and the national and international movement of goods and people on old and new foodborne threats.

Recognizing and Diagnosing Foodborne Illness

The typical presentations associated with foodborne illness are usually gastrointestinal, such as vomiting, diarrhea, and abdominal pain. Upon suspicion of a foodborne illness, the following are important questions for a physician or other healthcare professional to ask the patient[1]:

  • What symptoms have you been experiencing?

  • How long have you been experiencing these symptoms?

  • Do any of your close friends or family members have similar symptoms?

  • What is your occupation? Do any of your coworkers have similar symptoms?

  • Have you recently been hospitalized? If so, what was the reason for your hospitalization?

  • Are you currently using any medication?

  • Are you sexually active?

  • Have you ever resided in a nursing home residence?

  • Are you in contact with children on a regular basis?

  • Have you ingested any raw or poorly cooked food, unpasteurized milk or juices, home-canned goods, fresh produce, or soft cheeses made from unpasteurized milk?

  • Have you recently traveled or taken a camping trip? Do you live on or have you visited a farm? Have you had contact with an animal or pet?

  • Before you began experiencing your current symptoms, when was the last time you were sick? What was the associated or preceding illness? What medication did you use?

It is not recommended that the healthcare practitioner attempt to identify the source of the illness. This should be left to appropriate public health authorities. It is therefore essential that a good history is elicited and recorded to assist public health authorities if the need arises.

Gastrointestinal symptoms are the most common presentation for foodborne illness. Other symptoms that may be present in combination with gastrointestinal symptoms include fever, rash, myalgia, arthralgias, neurologic symptoms (paresthesias, weakness, and paralysis), and malaise. Strong clinical suspicion is needed because many of these symptoms resemble viral illness. Timing of symptoms, as well as specificity of symptoms, must be elicited from the patient to assist in differentiating one from the other. Clinicians should pay particular attention to known immunocompromised individuals as well as the very young and the elderly. Bloody diarrhea; weight loss; diarrhea leading to dehydration; fever; prolonged diarrhea (3 or more unformed stools per day, persisting for several days); neurologic involvement, such as paresthesias, motor weakness, or cranial nerve palsies; sudden onset of nausea, vomiting, or diarrhea; and severe abdominal pain are signs and symptoms occurring alone or in combination that require laboratory testing to provide important diagnostic clues.[1]

The preceding signs and symptoms may also be associated with non-foodborne diseases, such as irritable bowel syndrome and inflammatory bowel disease. As such, a history and physical examination should be completed to elicit signs and symptoms that would support these diagnoses. In most cases, chronicity of signs and symptoms is enough to provide the needed clues, but laboratory testing may give further proof. Other diagnoses that should be considered include malabsorption, malignancy, gastrointestinal tract surgery or radiation, structural or functional gastrointestinal blockage for various reasons (eg, worm infestation), and genetic or diet-related metabolic deficiencies.

Healthcare providers should also pay special attention to patients with neurologic symptoms because this may raise suspicion for potential life-threatening diagnoses, such as ingestion of contaminated seafood, mushroom poisoning, chemical poisoning, and ingestion of certain toxins (eg, botulinum toxin, tetrodotoxin) and chemicals (eg, organophosphates).

Laboratory Tests and Etiologic Agents

The most important laboratory test is a specimen collection. This should be done as soon as possible, and the specimen should be properly preserved. The specimen or the results should be reported to the appropriate public health authorities in the jurisdiction because all cases seen should be considered as possible index cases of a potential outbreak.

Healthcare professionals are encouraged to understand routine specimen collection and testing procedures, as well as circumstances and procedures for making special test requests. Healthcare professionals are also advised to be aware of the limitations of the laboratories they use in the event that more complex or special tests are indicated. Again, early communication with public health authorities is required in such situations.

Microscopy is recommended on all collected samples. The presence of leucocytes on microscopy suggests diffuse colonic inflammation and invasive bacterial infection. Stool culture is recommended in this instance. Stool cultures are indicated in such circumstances as an immunocompromised patient, a febrile patient, or a patient with bloody diarrhea or persistent illness.

Most laboratories limit routine stool cultures to screening for Salmonella and Shigella species and Campylobacter jejuni or E coli. Because cultures for Vibrio and Yersinia species, E coli O157:H7, and Campylobacter species other than C jejuni or C coli require additional media or incubation conditions, advanced notification or communication with laboratory and infectious disease personnel is needed in these cases.

Stool examination for parasites is indicated for immunocompromised patients, patients with suggestive travel history, and patients with persistent illness or illness unresponsive to treatment. Stool examination for infection with Cryptosporidium species and Cyclospora cayetanensis will require special laboratory procedures, and this must be considered when specimens are being submitted in suspected cases.

The Table lists clinical presentations and potential food-related agents to consider in each instance. Other tests that may provide additional diagnostic clues include a complete blood count, blood culture, testing of food samples and vomitus, endoscopy, imaging tests, and certain neurologic tests.

Table. Etiologic Agents to Consider for Various Manifestations of Foodborne Illness

Clinical Presentation Potential Food-Related Agents to Consider
Gastroenteritis (vomiting as primary symptom; fever and/or diarrhea also may be present) Viral gastroenteritis, most commonly rotavirus in an infant or norovirus and other caliciviruses in an older child or adult; or food poisoning due to preformed toxins (eg, vomitoxin, Staphylococcus aureus toxin, Bacillus cereus toxin) and heavy metals.
Noninflammatory diarrhea (acute watery diarrhea without fever/dysentery; some patients may present with fever)a Can be caused by almost all enteric pathogens (bacterial, viral, parasitic) but is a classic symptom of infection with:
  • Enterotoxigenic Escherichia coli

  • Giardia species

  • Vibrio cholerae

  • Enteric viruses (astroviruses, noroviruses, other caliciviruses, enteric adenovirus, rotavirus)

  • Cryptosporidium species

  • Cyclospora cayetanensis

Inflammatory diarrhea (invasive gastroenteritis; grossly bloody stool and fever may be present)b
  • Shigella species

  • Campylobacter species

  • Salmonella species

  • Enteroinvasive E coli

  • Enterohemorrhagic E coli

  • E coli O157:H7

  • V parahaemolyticus

  • Yersinia enterocolitica

  • Entamoeba histolytica

Persistent diarrhea (lasting > 14 days) Prolonged illness should prompt examination for parasites, particularly in travelers to mountainous or other areas where untreated water is consumed. Consider Cyclospora cayetanensis, Cryptosporidium species, Entamoeba histolytica, and Giardia lamblia
Neurologic manifestations (eg, paresthesias, respiratory depression, bronchospasm, cranial nerve palsies)
  • Botulism (Clostridium botulinum toxin)

  • Organophosphate pesticides

  • Thallium poisoning

  • Scombroid fish poisoning (histamine, saurine)

  • Ciguatera fish poisoning (ciguatoxin)

  • Tetraodon fish poisoning (tetrodotoxin)

  • Neurotoxic shellfish poisoning (brevetoxin)

  • Paralytic shellfish poisoning (soxitoxin)

  • Amnesic shellfish poisoning (domoic acid)

  • Mushroom poisoning

  • Guillain-Barré syndrome (associated with infectious diarrhea due to Campylobacter jejuni)

Systemic illness (eg, fever, weakness, arthritis, jaundice)
  • Listeria monocytogenes

  • Brucella species

  • Trichinella spiralis

  • Toxoplasma gondii

  • Vibrio vulnificus

  • Hepatitis A and E viruses

  • Salmonella typhi and Salmonella paratyphi

  • Amebic liver abscess

aNoninflammatory diarrhea is characterized by mucosal hypersecretion or decreased absorption without destruction and generally involves the small intestine. Some affected patients may be dehydrated because of severe watery diarrhea and may appear seriously ill. This is more common in the young and the elderly. Most patients experience minimal dehydration and appear mildly ill with scant physical findings. Illness typically occurs with abrupt onset and brief duration. Fever and systemic symptoms usually are absent (except for symptoms related directly to intestinal fluid loss).
bInflammatory diarrhea is characterized by mucosal invasion with resulting inflammation and is caused by invasive or cytotoxigenic microbial pathogens. The diarrheal illness usually involves the large intestine and may be associated with fever, abdominal pain and tenderness, headache, nausea, vomiting, malaise, and myalgia. Stools may be bloody and may contain many fecal leukocytes.
From the Foodborne Illness Primer Work Group.[1] Adapted with permission.

Treatment of Foodborne Illness

Most episodes of foodborne illness are characterized by gastrointestinal symptoms of acute gastritis. These episodes are typically self-limiting and require only fluid replacement and supportive care, such as medications to control symptoms. This is the management of choice in most instances after careful history, examination, and tests if needed. However, it is important to note that antidiarrheal agents are not recommended in children because they could lead to potential adverse health effects. Oral rehydration is indicated and appropriate for patients who can tolerate it, and the report provides information on drinking when thirsty and after episodes of fluid loss (diarrhea or vomiting). It is also important to drink appropriate liquids, avoiding fluids that may worsen symptoms, such as sodas, fruit juices, alcohol, and coffee. Intravenous therapy is indicated in more severe cases. When indicated, choice of antimicrobial use should be made on the basis of:

  • Clinical signs and symptoms;

  • Organism detected in clinical specimens;

  • Antimicrobial susceptibility tests; and

  • Appropriateness of treating with an antibiotic (some enteric bacterial infections are best not treated).

Antimicrobial use should be judicious in order to avoid development of microbial drug resistance. Therefore, healthcare professionals should be aware of the antimicrobial resistance patterns in the patient's presenting community. Additionally, adequate follow-up with the patient must take place to confirm treatment effectiveness. Botulinum antitoxin can prevent progression of neurologic symptoms in early phase of illness; it is therefore indicated in such cases.

Foodborne Illness, Healthcare Professionals, and Public Health

The United States began reporting foodborne illnesses more than 50 years ago. Concerned about the ever-rising morbidity and mortality rates caused by diseases, such as typhoid and infantile diarrhea, state health officials urged that these "enteric fevers" be properly investigated and reported. The goal of the investigations was to obtain information about the role of food, milk, and water in outbreaks of gastrointestinal tract illness as the basis for public health actions. These early reporting efforts led to the enactment of important public health measures (eg, the Pasteurized Milk Ordinance)[4] that profoundly decreased the incidence of foodborne illnesses.

Many times, healthcare professionals suspect foodborne illness because of the organism involved or because of other available information, such as the existence of several ill patients in the surrounding communities who have eaten the same food. Healthcare professionals serve as the eyes and ears for the health department and provide important information to local and state public health authorities. Foodborne disease reporting not only is important for disease prevention and control but also helps ensure that more accurate assessments of the burden of foodborne illness in the community occur when such cases are reported. Additionally, practicing clinicians help health officials identify and follow the disease outbreak in a community by reporting cases of foodborne illness. This may lead to early identification and removal of contaminated products from the commercial market and can help contain the outbreak. For example, if a restaurant or other food service establishment is identified as the source of the outbreak, health officers will work to correct any inadequate food preparation practices. If the home is the likely source of the contamination, health officers can institute public education about proper food-handling practices. Occasionally, reporting may lead to the identification of a previously unrecognized agent of foodborne illness and can sometimes lead to the identification and appropriate management of human carriers of known foodborne pathogens, especially those with high-risk occupations for disease transmission (such as food workers).

If foodborne illness is suspected, healthcare providers should follow normal protocols and follow-up with local or state health departments to help identify a notifiable foodborne disease. Also, because many times it is unclear whether a patient has a foodborne illness before diagnostic tests, healthcare professionals should also report potential foodborne illnesses, especially when 2 or more patients present with a similar illness that may have resulted from the ingestion of a common food. After this step, local health departments report the illnesses to the state health departments and determine whether further investigation is warranted.

Each state health department reports foodborne illnesses to the Centers for Disease Control and Prevention (CDC), which compiles the data at a national level and disseminates information weekly to health officials and the public via the MMWR and annual summary reports. The CDC assists local and state public health authorities with epidemiologic investigations and the design of interventions to prevent and control food-related outbreaks. The CDC also coordinates a national network of public health laboratories, called PulseNet, which performs "molecular fingerprinting" of bacteria (via pulsed-field gel electrophoresis) to support such epidemiologic investigations.

In addition to reporting cases of potential foodborne illnesses, it is important for clinicians to report noticeable increases in unusual illnesses, symptom complexes, or disease patterns (even without definitive diagnosis) occurring in surrounding communities to public health authorities. This allows public health officials to initiate an epidemiologic investigation as soon as possible.[1]


Physicians and other healthcare professionals have a critical role in the prevention and control of food-related disease outbreaks. Therefore it is important for them to have the tools needed to help identify and understand foodborne illnesses. With new information constantly emerging, physicians and other healthcare professionals should be aware of the most current recommendations on food safety in order to diagnose, treat, report, and prevent foodborne illnesses.


This article uses information with permission from the Foodborne Illness Primer Work Group.[1] Special thanks to Michael L. Clark, RN, for contributing and reviewing earlier drafts of the column.


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