Foodborne and Waterborne Illness: Diagnosis

A detailed history to assess changes in the patient’s bowel pattern and temporal relationships with exposures to food, antibiotics, sick persons, or travel (including hiking and camping) is important. The history may help determine whether the condition is likely to be self–limited or requires treatment. In addition, the history points toward likely causative organisms that may be candidates for testing. For example, a history of blood or mucus in the diarrhea warrants stool examination. Laboratory evaluation usually includes culture, leukocyte count, fecal occult blood testing, and possibly screening for ova and parasites.

Acute diarrhea diagnosis in the clinical setting is based on an increased frequency and looser consistency of stools. Diarrhea is defined as 6 or more soft or waterlike daily stools, although episodes vary considerably. Severe bacterial cases may cause diarrhea every 30 minutes. Viruses, especially noroviruses, cause the majority of gastroenteritis cases. The major clinical decision for severe or persistent diarrhea is whether supportive therapy (ie, oral or intravenous rehydration therapy for volume depletion) is sufficient, or whether pathogen–focused antibiotics are required. Note: Antibiotics are rarely needed.

Irritable bowel syndrome, inflammatory bowel disease, malabsorption syndromes (eg, celiac sprue, gluten, and other food intolerances), and hyperthyroidism should be considered in the differential if the diarrhea does not resolve within 1 to 2 weeks.

Diarrheal Illness

Salmonella. This widespread foodborne illness occurs in 2 main types: typhoid fever and nontyphoidal infection. Typhoid fever classically presents systemically with fever, hepatomegaly, and splenomegaly, and a tender abdomen, but it may also include rash (ie, a classic “rose spot” skin lesion) and diarrhea or constipation. Nontyphoidal salmonella infection typically presents with nausea, vomiting, diarrhea, and fever, and is the most common cause of foodborne gastroenteritis in the United States. Illness usually occurs due to undercooked poultry, cross–contamination of other foods or cooking surfaces, and raw or undercooked eggs (including egg–containing products, such as mayonnaise and custards, left at room temperature).

Milk, meat, and fecally contaminated fresh produce, such as alfalfa sprouts, may also transmit disease, as can pet reptiles. Disease occurs more commonly in the summer and fall. Particularly susceptible are individuals with inflammatory bowel disease, lymphomas, and altered bowel flora (eg, due to antibiotics). Bloody diarrhea may occur.

Carriers of Salmonella typhi (eg, the infamous cook “Typhoid Mary” in early 20th century New York) occasionally cause typhoid fever epidemics.

Campylobacter. The second most common cause of foodborne illness in the United States is Campylobacter jejuni. Undercooked poultry and cross–contamination of other foods are the most likely sources. On average, 60% of retail poultry products throughout the world,⁴ and up to 88% in the United States,⁵ are contaminated with campylobacter. Bloody diarrhea may also occur with campylobacter infection.

Shigella. The third most common cause of foodborne illness in the United States, Shigella flexneri, is a highly infectious (an inoculum of just 10 organisms can cause infection) and pathogenic bacterium that often causes bloody diarrhea. Other complications include hemolytic uremic syndrome and thrombotic thrombocytopenic purpura. It spreads through food, water, or person–to–person contact, and is common in nursing homes and daycare settings.

Cryptosporidium parvum. This parasite is transmitted through ingestion of C parvum eggs in contaminated or inadequately filtered water, or exposure to cows and their manure. In addition to being a common water contaminant, it can contaminate produce and unpasteurized milk. Cryptosporidium is a common infectious agent in pools and spas and can also spread from person to person.⁶

Escherichia coli. The E coli O157:H7 strain is spread most often through undercooked hamburger. Unpasteurized juice and raw produce contaminated by cattle manure may also be sources. It may cause bloody diarrhea and can lead to the hemolytic uremic syndrome and thrombotic thrombocytopenic purpura. Like salmonella, it usually occurs in the summer and fall. Other more common E coli strains may also cause diarrheal illness, such as enterohemmorhagic and enteroinvasive E coli.

Yersinia enterocolitica. This bacterial infection typically comes from undercooked pork, unpasteurized milk, or contaminated water.

Vibrio cholerae. This bacterial infection results in a secretory diarrhea. It occasionally occurs along the Gulf Coast from contaminated water. Vibrio parahaemolyticus infection is due to ingestion of contaminated shellfish.  

Cyclospora cayetanensis. A parasitic infection acquired from produce exposed to contaminated water and from person–to–person contact, it may cause prolonged diarrhea and systemic symptoms, such as fatigue.

Bacillus cereus. A bacterium that can multiply in underheated foods, such as rice, it is often found in food left under heating lamps. B cereus produces toxins that typically cause rapid–onset vomiting and may also cause diarrhea.

Staphylococcus aureus. The toxins produced by S aureus may cause symptoms similar to those caused by B cereus. Common sources include contaminated salads, eggs, meat, and dairy products that have been prepared and left at room temperature.

Clostridium perfringens. Found in contaminated meat and poultry, it produces toxins after ingestion.

Viral gastroenteritis. Norovirus is the most common viral cause of gastroenteritis and may cause vomiting and explosive diarrhea. It occurs in families and among persons living in other close quarters, such as cruise ships, and can be transmitted through the air and via the fecal–oral route. Rotavirus, adenovirus, and astrovirus are other viral causes of intestinal illness.

Giardia lamblia. This very common intestinal parasite is often found in mountain streams due to fecal contamination by beavers and bears. It is also spread through food and person–to–person (fecal–oral) contact.

Entamoeba histolytica. An infection occurring worldwide, it is prevalent in tropical regions. In addition to causing painful profuse diarrhea with blood and mucus, amoebic infection may also cause ulcers on the anus and liver abscesses with systemic symptoms. It can be transmitted sexually, as well as by consumption of contaminated water.

Nondiarrheal Illness

Hepatitis A. This virus can be contracted through water, produce (eg, strawberries and cantaloupe), milk, and raw shellfish. Spread usually occurs through cross–contamination by an infected food handler at any point from the farm to the plate. Fecal–oral transmission may also occur through sexual contact.

Listeria monocytogenes causes listeriosis and is fatal in nearly 20% of cases. The most common manifestations include bacteremia and meningitis, particularly in infants and the elderly. This organism is the basis for the warning to pregnant women not to consume unpasteurized soft cheeses, particularly from Latin America. Raw hot dogs and deli meats are also high–risk foods. Less commonly, one may develop gastroenteritis related to listeriosis.

Clostridium botulinum causes a life–threatening paralysis and may result from home canning, fish fermentation, and extended use of food warmers.

Toxoplasma gondii infection may occur through ingestion of raw beef or lamb or through cross–contamination from cat feces (eg, in infrequently cleaned litter boxes and gardens). Infection is generally self–limited and asymptomatic, except in immunocompromised patients. However, primary infection with toxoplasmosis during pregnancy is dangerous to the fetus. Immunocompetent individuals may develop a mononucleosis–like syndrome. With T–cell immunodeficiencies, such as HIV or those in heart transplant recipients, the organism often causes brain, retinal, lung, and muscle lesions.

Trichinosis. This disease is caused by ingestion of encysted larvae in undercooked pork and wild carnivorous game, such as bear. Cattle and horse meat can be cross–contaminated. Trichinosis rarely causes diarrhea, but may cause ocular, cardiac, neurologic, and muscular symptoms such as muscle swelling and pain after larval migration. It is now rare in the United States, due to regulatory controls on the feeding of pigs.

Echinococcus. This parasite may be ingested in water contaminated by wild and domestic canines (eg, foxes and wolves), particularly in the Middle East, Greece, Africa, and Asia. Cysts may infect the liver and lungs.

Brucellosis.  Brucellosis, particularly B abortus, B melitensis,and B suis, is found in contaminated dairy and meat products, commonly from Latin America. Brucellosis may result in high fevers, septicemia, septic arthritis, meningitis, osteomyelitis, and rashes.

Tapeworms can result from eating raw fish, beef, and pork. Cysticercosis occurs through raw pork ingestion. Migration to the brain may result in seizures, and migration to the skin and liver may also occur. In rare instances, fish tapeworms may cause pernicious anemia due to vitamin B₁₂ malabsorption. Beef tapeworms are asymptomatic.

Fish toxins, such as ciguatera and scombroid, can become concentrated in larger fish. Cigutera is associated with neurologic/cardiovascular complications, while histamine–related complications are associated with scombroid. In addition, tetrodotoxin in puffer fish is often fatal due to multiorgan system collapse.

Prions are abnormal proteins that cause slowly progressive spongiform encephalopathies, including Creutzfeldt–Jakob disease and bovine spongiform encephalopathy (BSE, or “mad cow disease”). The latter disease emerged in the mid–1990s in Great Britain, presumably due to the practice of feeding cattle the remains of other ruminants, particularly sheep (sheep are susceptible to a similar spongiform encephalopathy called scrapie). Evidence suggests that human cases of variant Creutzfeldt–Jakob disease have been due to prion transmission through consumption of infected cattle.⁷ The risk to humans has been reduced by regulations for livestock feeding and processing that helps prevent ingestion of concentrated neural material (ie, brain and spinal cord). Similar diseases occur in other animals, such as chronic wasting disease in deer and elk.