Food-Borne Illnesses: A Primary Care Primer

August 1, 2004

Backyard cookouts . . . picnics at the beach . . . these warm-weather pleasures can heighten your patients' risk of exposure to food-borne pathogens. An egg salad sandwich, left in the hot sun too long, can become a breeding ground for Salmonella, and undercooked burgers can harbor Escherichia coli O157:H7.

Backyard cookouts . . . picnics at the beach . . . these warm-weather pleasures can heighten your patients' risk of exposure to food-borne pathogens. An egg salad sandwich, left in the hot sun too long, can become a breeding ground for Salmonella, and undercooked burgers can harbor Escherichia coli O157:H7.

Although most food-related illnesses are self-limited, elderly, very young, and immunocompromised patients may face serious and even life-threatening complications if they are not treated. Each year about 76 million persons become ill, more than 300,000 are hospitalized, and about 5000 die as a direct result of food-borne illnesses.1

Because the GI symptoms of food poisoning resemble viral gastroenteritis, making an early, accurate diagnosis can be difficult. Summarized here are tips from the CDC on recognizing-as well as treating and reporting-food-borne illness.1

HOW TO RECOGNIZE FOOD-BORNE ILLNESS

Clues in the history. Keys to determining the origin of a food-borne pathogen infection are:

Length of the incubation period.

Duration of the illness.

Predominant symptoms.

Involvement of other persons with similar illness.

Ask the patient about:

Consumption of raw or undercooked foods (eg, eggs, meats, shellfish [Figure], fish), unpasteurized milk or juices, home-canned goods, fresh produce, or soft cheeses made from unpasteurized milk.

Similar symptoms in family members or close friends.

Occupation, contact with pets or farm animals, day-care attendance, foreign travel, trips to coastal regions, camping trips to areas where treated water is unavailable, or attendance at group picnics or similar outings.

Suggestive symptoms. In a patient who has GI symptoms, a viral infection must be ruled out. The absence of myalgias or arthralgias would make a viral syndrome less likely. However, bear in mind that food-borne illnesses that target the CNS can produce paresthesias, weakness, and paralysis. Bloody diarrhea suggests a food-borne pathogen infection, especially if this symptom occurs early in the illness. Table 1 lists symptoms of food-borne illness and possible causative pathogens.

Other conditions to consider in the differential of GI illness. These include underlying medical conditions such as irritable bowel syndrome; inflammatory bowel diseases such as Crohn disease or ulcerative colitis; malignancy; medication use (including antibiotic-related Clostridium difficile toxin colitis); GI tract surgery or radiation; malabsorption syndromes; and immune deficiencies.

LABORATORY TESTS

Consider ordering laboratory tests if any of the following signs and symptoms are present (particularly in very young, elderly, or immunocompromised patients):

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.

Severe abdominal pain.

Note that the protocols used to detect pathogens differ among clinical microbiology laboratories. Be aware of circumstances and procedures for making special test requests, such as toxin testing, serotyping, and molecular techniques.

Stool cultures are indicated if your patient is immunocompromised, febrile, has bloody diarrhea, has severe abdominal pain, or has a high fecal leukocyte count, or if the illness is clinically severe or persistent. In most laboratories, routine stool cultures screen only for Salmonella and Shigella species, Campylobacter jejuni, and Campylobacter coli. Give advance notification to the laboratory if you suspect infection with Vibrio or Yersinia species, E coli O157:H7, or Campylobacter species other than Cjejuni or C coli, because these pathogens require additional media or incubation conditions.

Examination of the stool for parasites is generally indicated only for patients with significant recent travel histories, those who are immunocompromised, and those who have chronic diarrhea or diarrhea that fails to respond to appropriate antibiotic therapy. Routine stool examination for ova and parasites can identify Giardia lamblia and Entamoeba histolytica; however, a special request is often needed to test for Cryptosporidium and Cyclospora cayetanensis.

TREATMENT

Although many episodes of acute GI illness are self-limited and nothing more than rest and oral rehydration is required, patients with more severe cases of gastroenteritis may require intravenous rehydration. Avoid anti-diarrheal agents in children and infants, because these patients are at risk for severe adverse effects from these drugs. If antimicrobial therapy is necessary, base your selection on:

Clinical signs and symptoms.

Organism detection in clinical specimens.

Antimicrobial susceptibility tests.

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

Treat suspected cases of botulism promptly with botulinum antitoxin to prevent the progression of neurologic dysfunction. Notify your local and state health departments if you suspect botulism. The CDC maintains a 24-hour service to assist health care providers with the diagnosis and management of botulism.

SURVEILLANCE AND REPORTING

Primary care clinicians serve as the "eyes and ears" for health departments by providing information regarding possible outbreaks of food-borne disease. Table 2 lists the current reporting requirements for food-borne diseases and conditions in the United States.

When you identify a notifiable disease, contact the local or state health department. Also report potential food-borne illnesses, such as when 2 or more patients present with similar symptoms that may have resulted from the ingestion of a common food. In addition, it is advisable to report noticeable increases in unusual illnesses, symptom complexes, or disease patterns (even without definitive diagnosis) to public health authorities. n

References:

REFERENCE:

1. Centers for Disease Control and Prevention. Diagnosis and management of foodborne illnesses: a primer for physicians and other health care professionals. MMWR. 2004;53(RR-4):1-29.