Approach
Characteristic history is essential to diagnose foodborne illness or poisoning.
History
It is important to determine food exposure, exposure to animals, duration of disease, the presence of local outbreaks of foodborne illnesses, contact history, substance abuse history, and travel history (especially foreign travel). If 2 or more people have symptoms, then this is considered an outbreak. Certain pathogens are notifiable.
Specific food exposures to identify include the following:[34][40]
Undercooked meat: associated with Salmonella, Campylobacter, Shiga toxin-producing Escherichia coli, Clostridium perfringens, Yersinia, Staphylococcus aureus, Trichinella, and hepatitis E[24]
Raw seafood: associated with norovirus, Vibrio species, hepatitis A, Plesiomonas, or trematoda (flukes); raw or cooked seafood may also be associated with toxin contamination (e.g., marine toxins, mercury, cadmium, histamine)
Homemade canned foods: associated with Clostridium botulinum
Unpasteurized milk, soft cheeses, or other raw dairy products: associated with Listeria, Salmonella, Campylobacter, Shiga toxin-producing E coli, Yersinia, S aureus, Cryptosporidium, Brucella, Mycobacterium bovis, and Coxiella burnetii
Deli meats, cheeses, or salads: associated with Listeria
Fruits, vegetables, or unpasteurized fruit juice: associated with Shiga toxin-producing E coli, nontyphoidal Salmonella, Cyclospora, Cryptosporidium, norovirus, hepatitis A, and Listeria
Raw eggs: Salmonella
Mushrooms: associated with mushroom poisoning.
Improper food handling and storage
Associated with a higher risk of developing and transmitting foodborne illness.
Examples include:[1][17][20][25][26]
improper refrigeration and storage (home-canning)
not rinsing cutting boards and sinks before and after washing fresh produce
not keeping raw animal products separated from fresh produce in the refrigerator, or when transporting from shop to home
not using a meat thermometer to determine whether meat is cooked
not refrigerating foods promptly
putting large quantities of hot food in the refrigerator without portioning into smaller amounts
thawing frozen food on the counter
using refrigerators that are too warm (≥43°F [6°C]) for safe storage of food.
Specific patient populations who may be at increased risk
A history of foreign travel should prompt suspicion of infections endemic to the region of travel.
Older people and pregnant women are more vulnerable to foodborne illness and to a more severe illness that may require hospitalization and is associated with higher morbidity and mortality. Some chronic diseases (e.g., diabetes and cancer) and use of immunosuppressive medications (e.g., corticosteroids, antitumor necrosis factor medicines, and chemotherapies) increase a patient's vulnerability to opportunistic infections.[17][20][21] People with alcohol-use disorder and people with chronic liver disease (hemochromatosis or cirrhosis) are at increased risk of infections due to Vibrio vulnificus from raw shellfish.[22] The use of gastric acid suppression has been associated with an increased risk of enteric infections.[27][28][29]
Many risk factors for food poisoning are closely associated and may have synergetic effect.[1]
Symptoms may suggest the underlying pathologen
Characteristics and frequency of bowel movements, associated abdominal and systemic symptoms and/or vomiting may suggest the underlying pathogen.
With reference to diarrhea, the World Health Organization (WHO) defines 3 clinical types:[43]
acute watery; lasts several hours or days (includes cholera)
acute bloody (dysentery)
persistent; lasts 14 days or longer.
The presence of blood or mucus in the stool indicates invasion of the intestinal or colonic mucosa. Proctitis syndrome, seen with shigellosis, is characterized by tenesmus, rectal discomfort, and frequent painful bowel movement containing blood, pus, and mucus. Profuse rice-water stool suggests cholera or a similar enterotoxigenic process. This leads to large-volume watery stools in the absence of blood, pus, or severe abdominal pain. Profound dehydration may result.
Parasitic infections are more likely to cause persistent diarrhea than bacterial causes.[3] Trematodiasis is a challenge to diagnose due to the insidious onset of symptoms, which are often vague and depend on the fluke species involved. Patients can present with hepatobiliary symptoms (e.g, abdominal pain, jaundice, right upper quadrant pain), pulmonary symptoms (e.g., chronic cough, chest pain, dyspnea, hemoptysis), or intestinal symptoms (e.g., mucosal ulceration, malnutrition).[5]
Abdominal pain is commonly severe in inflammatory processes. Painful abdominal muscle cramps suggest underlying electrolyte loss, as in severe cholera. Yersinia enterocolitis may mimic the symptoms of appendicitis or Crohn ileitis (right lower quadrant pain and guarding), as can trematodiasis.
Bloating for a relatively long period should raise the suspicion of giardiasis.
When vomiting is the major presenting symptom, Staphylococcus aureus, Bacillus cereus, norovirus, or rotavirus is suspected. Ingestion of poisonous mushrooms or heavy metals may also present with nausea and vomiting.[2]
Physical examination
The presence of tachycardia, tachypnea, pyrexia, and altered conscious level would indicate severe illness. Abdominal exam may be unremarkable, or demonstrate diffuse or localized tenderness, and in some patients the abdomen may be distended. An assessment of dehydration should be made.
The WHO classifies the degree of dehydration on a scale of 1-3:[43]
No dehydration; with no signs or symptoms
Some dehydration; which is indicated by two or more of these signs: thirst, restless or irritable behavior, decreased skin elasticity, and sunken eyes
Severe dehydration; in which symptoms become more severe, indicated by two or more of these signs: diminished consciousness/lethargy, sunken eyes, unable to drink or drink poorly, and skin pinch goes back very slowly (≥2 seconds).
Dehydration is less likely with inflammatory diarrhea than with noninflammatory diarrhea because inflammatory diarrhea is usually a disease of the colon, is not toxin-mediated, and usually results in smaller stool volume.
There can be a broad spectrum of possible extra-intestinal symptoms including skin (e.g., rose spot macules in Salmonella typhior erythema nodosum in Yersinia infection), musculoskeletal (e.g., reactive arthritis occurring 1 to 3 weeks after infection with Salmonella, Shigella, Campylobacter, and Yersinia infections), and neurologic manifestations (e.g., diplopia, reduced muscle tone, and slurred speech seen with botulism).
Patients with trematodiasis may present with features of biliary colic, cholestasis, cholelithiasis, hepatic abscess, or hepatitis.[5] Ectopic infection from trematodiasis can include central nervous system, heart, reproductive organ, spleen, skin, or blood vessel manifestations.
If a stool sample cannot be provided a digital rectal exam can be performed to test for occult blood and to obtain a rectal swab for culture.
Laboratory tests
In general, laboratory evaluation is not required in patients with mild and uncomplicated illness, which is usually self-limiting.
Laboratory workup is indicated for severe disease (e.g., blood in stool, fever, diarrhea leading to dehydration); for patients at high risk of severe disease; when noninfectious causes (toxins or chemicals) are suspected; or when identification of the pathogen is needed to guide management or public health efforts.[1][40]
Initial tests should include:
Basic metabolic panel: to rule out electrolyte abnormalities and renal dysfunction in all patients with evidence of moderate or severe dehydration, and in those with severe vomiting or diarrhea or symptoms without improvement after 24 hours. Hemolytic uremic syndrome is suspected when uremia is present.
Complete blood count (CBC) with differential: in patients presenting with blood in stool, fever, suspected invasive pathogens (e.g., Shiga toxin-producing Escherichia coli [e.g., O157:H7]), and extragastrointestinal manifestations. Helps to assess the inflammatory response and the degree of hemoconcentration, and may detect evidence of hemolytic uremic syndrome when Shiga toxin-producing E coli is suspected.
Stool microscopy:
For white blood cells (WBCs) and red blood cells in patients presenting with blood in stool, fever, suspected invasive pathogens (e.g., Shiga toxin-producing E coli [e.g., O157:H7]), and when other diagnoses are considered (e.g., inflammatory bowel disease, ischemic or infectious colitis), and with symptoms of 3 days or more.
Includes exam of the stool for ova and parasites (including trematode eggs), performed on all samples, when a stool sample is indicated. Recommended in immunocompromised patients, patients with persistent diarrhea, and when the patient has visited an area where parasites are endemic.[40][44] Do not routinely order a comprehensive stool ova and parasite microscopic exam in all patients presenting with diarrhea.[45] The comprehensive ova and parasite microscopic exam often requires submission of multiple stool samples. It is labor intensive, requires significant expertise to perform, and typically has lower sensitivity when compared to other available tests.[45]
Dark-field microscopy can be included to identify Vibrio cholerae if suspected.
Stool culture:
Guidelines recommend stool testing for Salmonella, Shigella, Campylobacter, Yersinia, Clostridioides difficile, Shiga toxin-producing E coli, and Entamoeba in people with diarrhea accompanied by fever, bloody or mucoid stools, severe abdominal cramping or tenderness, or signs of sepsis.[40]
Testing for additional organisms may be considered depending on the clinical scenario.[3] Testing for Yersinia enterocolitica should be arranged in people with persistent abdominal pain and in people with fever at epidemiologic risk for yersiniosis.[40] In individuals with addition with large volume rice water stools or either exposure to salty or brackish waters, consumption of raw or undercooked shellfish, or travel to cholera-endemic regions within 3 days prior to onset of diarrhea, test stool specimens for Vibrio species.[40]
Stool serologic testing and toxin testing can help diagnose the type of Shiga-toxin producing bacteria, and also which toxin is being produced. Testing for Yersinia typically involves serologic testing with a repeated level 2 weeks later, but local infectious disease consult is recommended.
Other tests to consider:
Polymerase chain reaction: some centers are moving to polymerase chain reaction sequencing to detect a number of bacterial, viral, and parasitic infections (e.g., Campylobacter, Salmonella, Shiga toxin-producing E coli O157, Giardia, Cryptosporidium).[3][46][47] Useful in detecting viruses, such as norovirus, and in differentiating pathogenic from nonpathogenic Entamoeba species.[3][48]
Clostridioides difficile (formerly known as Clostridium difficile) toxin test: to exclude C difficile diarrhea.
Blood culture: if the patient is febrile (e.g., temperature >101°F [>38.4°C]) and there are signs of sepsis (e.g., tachycardia, hypotension, poor capillary refill, tachypnea, acute mental confusion, decreased urine output), a blood culture should be taken to exclude bacteremia. Also recommended for immunocompromised people, people with signs of systemic infection, and when enteric fever is suspected.[40] Signs of sepsis may be difficult to differentiate from signs of severe dehydration. See Sepsis in adults.
Liver function tests (LFTs): to distinguish food poisoning from acute cholecystitis or acute hepatitis.
Hepatitis A and E serology: when there is evidence of deranged liver enzymes.
Serum lipase or amylase: should be ordered if severe abdominal pain, in order to rule out acute pancreatitis. Serum lipase testing is used in preference to serum amylase, but depends on local availability.[49][50]
Stool antigen tests: are improving the diagnostic yield of conditions such as Giardia and Cryptosporidium.
String test (entero-test): considered if stool microscopy fails to diagnose Giardia and antigen test is negative or unavailable. A capsule with a string in it is swallowed, with the free end of the string taped to the patient’s cheek. It is allowed to dissolve and the string passes into the duodenum where it is left for 4 to 6 hours before being removed. The string can then be examined for trophozoites. In some centers, polymerase chain reaction can be used to diagnose Giardia.
Consideration of differential diagnosis
The initial symptoms of diarrhea, vomiting, and abdominal pain may be common to a number of other differential diagnoses. If the patient develops symptoms that differ from those typical of foodborne illness, or there is no or inadequate response to treatment, a differential diagnosis should be considered.
Findings that would prompt additional investigations include:
Patients presenting with jaundice and/or significant abdominal pain; LFTs should be done for hepatitis and choledocholithiasis.
Suspected pancreatitis and patients with significant abdominal pain; in particular, epigastric pain with nausea and vomiting and abnormal liver tests, serum lipase or amylase should be requested. Serum lipase testing is used in preference to serum amylase.[49][50]
Other causes of abdominal pain/bloating with diarrhea should be considered, such as inflammatory bowel disease (needs CBC, C-reactive protein, abdominal x-ray, sigmoidoscopy/colonoscopy with biopsies, and small bowel radiology), ischemic colitis (needs sigmoidoscopy/colonoscopy with biopsies and cross-sectional imaging), celiac disease (exclude with endomysial antibodies/tissue transglutaminase and esophagogastroduodenoscopy with both D1 and quadrantic D2 biopsies), and C difficile-associated diarrhea (exclude with stool toxin test).
When there is a history or occupation (e.g., daycare, nursing) suggestive of exposure, or if LFTs are abnormal, hepatitis A screen is indicated.
Signs of botulism (cranial nerve palsies, oculobulbar weakness and descending, symmetrical flaccid paralysis in the absence of fever), serum, stool, gastric secretions, or food samples should be sent for toxin detection.[51] Do not await test results before administering botulinum antitoxin if the patient is symptomatic and botulism is suspected.[51]
Imaging/endoscopy/pathology
Imaging and endoscopic studies are unnecessary in mild uncomplicated diseases and in patients whose illness is resolving or improving.
Abdominal series should be ordered urgently in patients experiencing severe pain, or obstructive symptoms, or when perforation is suspected.
Sigmoidoscopy is considered in patients with bloody diarrhea in whom no enteric pathogen has been identified, with bloody diarrhea that persists or increases in severity, and in those patients whose clinical picture and tests results are incompatible with a diagnosis of foodborne illness. Sigmoidoscopy can be useful in diagnosing inflammatory bowel disease, antibiotic-associated diarrhea, shigellosis, and amebic dysentery. Obtaining a tissue biopsy is mandatory, though due to often demonstrating only acute inflammatory response, it is rarely helpful. Biopsy may distinguish inflammatory bowel disease from acute infectious enteritis or colitis by the presence of crypt architectural changes such as crypt branching or sparsity. However, these features take several weeks to develop and are not likely to be present in an infectious colitis. Electron microscopy of biopsied tissue is helpful when intracellular parasites (Cryptosporidium or Cyclospora cayetanensis) are suspected. A colonoscopy should be reserved for those in whom sigmoidoscopy does not yield a diagnosis, or in patients with persistent symptoms or are not responding to initial treatment.
Esophagogastroduodenoscopy with duodenal aspirate, with or without biopsy, is considered in immunocompromised patients, patients receiving chemotherapy and patients with persistent, severe symptoms lasting more than 5 days, and those not responding well to initial treatment. Duodenal aspirate is invasive, but may be used to diagnose Giardia, Strongyloides, Cystoisospora, or microsporidia infection when other tests have failed to reveal the diagnosis.[40]
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