Food poisoning is defined as an illness caused by the consumption of food or water contaminated with bacteria and/or their toxins, or with parasites, viruses, or chemicals. The most common pathogens are Norovirus, Escherichia coli, Salmonella, Clostridium perfringens, Campylobacter, and Staphylococcus aureus.
Signs and symptoms
The symptoms of food poisoning vary in degree and combination. They may include the following:
Abdominal pain: Most severe in inflammatory processes; painful abdominal muscle cramps suggest underlying electrolyte loss
Vomiting: Major presenting symptom of S aureus, B cereus, or Norovirus 
Diarrhea: Usually lasts less than 2 weeks
Fever: May be an invasive disease or an infection outside the GI tract
Stool changes: Bloody or mucousy if invasion of intestinal or colonic mucosa; profuse rice-watery if cholera or a similar process
Reactive arthritis: Seen with Salmonella, Shigella, Campylobacter, and Yersinia infections
Bloating: May be due to giardiasis
More serious cases of food poisoning can result in life-threatening neurologic, hepatic, and renal syndromes leading to permanent disability or death.
See Clinical Presentation for more detail.
See 5 Cases of Food Poisoning: Can You Identify the Pathogen?, a Critical Images slideshow, to help identify various pathogens and symptoms related to foodborne disease.
Examination of patients suspected of having food poisoning should focus on assessing the severity of dehydration. General findings may include the following:
Mild dehydration: A dry mouth, decreased axillary sweat, decreased urine
More severe volume depletion: Orthostasis, tachycardia, hypotension
Salmonella typhi infection: Upper abdominal rose spot macules, hepatosplenomegaly
Yersinia infection: Erythema nodosum, exudative pharyngitis
Vibrio vulnificus or V alginolyticus infection: cellulitis, otitis media
Always perform a rectal examination to (1) directly visualize the stool, (2) test occult blood, and (3) palpate the rectal mucosa for any lesions.
The following routine laboratory tests may help to assess the patient’s inflammatory response and the degree of dehydration:
CBC with differential
Serum electrolyte assessment
BUN and creatinine levels
Other laboratory studies can be helpful in cases of food poisoning and include the following:
Stool Gram staining and Loeffler methylene blue staining for WBCs: To help differentiate invasive disease from noninvasive disease
Microscopic examination of the stool: To detect any ova and parasites
Bacterial culture for enteric pathogens (eg, Salmonella, Shigella, Campylobacter organisms): Mandatory when a stool sample shows positive results for WBCs or blood or if patients have fever or symptoms persisting for longer than 3-4 days
Blood culture in febrile patients
C difficile assay: To help rule out antibiotic-associated diarrhea in patients receiving antibiotics or in those with a history of recent antibiotic use
Obtain flat and upright abdominal radiographs if the patient experiences bloating, severe pain, or obstructive symptoms or if the clinical picture suggests perforation.
Consider performing the following procedures when a stool examination is nondiagnostic, especially in immunocompromised patients:
Sigmoidoscopy/colonoscopy with biopsy
EGD with duodenal aspirate and biopsy
In patients with bloody diarrhea, sigmoidoscopy can be useful in diagnosing inflammatory bowel disease, antibiotic-associated diarrhea, shigellosis, and amebic dysentery.
See Workup for more detail.
Most food-borne illnesses are mild and improve without any specific treatment. Some patients have severe disease and require hospitalization, aggressive hydration, and antibiotic treatment. 
The main objective in managing patients with food poisoning is adequate rehydration and electrolyte supplementation, which can be achieved with either an oral rehydration solution or intravenous solutions in severely dehydrated individuals or those with intractable vomiting (eg, isotonic sodium chloride solution, lactated Ringer solution).
Patients should avoid milk, dairy products, and other lactose-containing foods during episodes of acute diarrhea, as these individuals often develop an acquired disaccharidase deficiency due to washout of the brush-border enzymes.
Medications that may be needed to treat patients with food poisoning include the following:
Antidiarrheals: Absorbents (eg, attapulgite, aluminum hydroxide); antisecretory agents (eg, bismuth subsalicylate); antiperistaltics (eg, opiate derivatives such as diphenoxylate with atropine, loperamide)
Antibiotics (eg, ciprofloxacin, norfloxacin, TMX/SMP, doxycycline, rifaximin): Selection of antibiotic depends on clinical setting and guided by microbiology and blood culture sensitivity results
The best ways to prevent food poisoning caused by infectious agents are as follows:
Practice strict personal hygiene
Cook all foods adequately
Avoid cross-contamination of raw and cooked foods
Keep all foods at appropriate temperatures (ie, refrigerated items: < 40°F; hot items: >140°F)
Food poisoning is defined as an illness caused by the consumption of food or water contaminated with bacteria and/or their toxins, or with parasites, viruses, or chemicals. The symptoms, varying in degree and combination, include abdominal pain, vomiting, diarrhea, and headache; more serious cases can result in life-threatening neurologic, hepatic, and renal syndromes leading to permanent disability or death.
Most of the illnesses are mild and improve without any specific treatment. Some patients have severe disease and require hospitalization, aggressive hydration, and antibiotic treatment. 
A food-borne disease outbreak is defined by the following 2 criteria:
- Similar illness, often GI, in a minimum of 2 people
- Evidence of food as the source
The pathogenesis of diarrhea in food poisoning is classified broadly into either noninflammatory or inflammatory types.
Noninflammatory diarrhea is caused by the action of enterotoxins on the secretory mechanisms of the mucosa of the small intestine, without invasion. This leads to large volume watery stools in the absence of blood, pus, or severe abdominal pain. Occasionally, profound dehydration may result. The enterotoxins may be either preformed before ingestion or produced in the gut after ingestion. Examples include Vibrio cholerae, enterotoxic Escherichia coli, Clostridium perfringens, Bacillus cereus,  Staphylococcus organisms , Giardia lamblia, Cryptosporidium,rotavirus, norovirus (genus Norovirus, previously called Norwalk virus), and adenovirus.
Inflammatory diarrhea is caused by the action of cytotoxins on the mucosa, leading to invasion and destruction. The colon or the distal small bowel commonly is involved. The diarrhea usually is bloody; mucoid and leukocytes are present. Patients are usually febrile and may appear toxic. Dehydration is less likely than with noninflammatory diarrhea because of smaller stool volumes. Fecal leukocytes or a positive stool lactoferrin test indicates an inflammatory process, and sheets of leukocytes indicate colitis.
Sometimes, the organisms penetrate the mucosa and proliferate in the local lymphatic tissue, followed by systemic dissemination. Examples include Campylobacter jejuni, Vibrio parahaemolyticus, enterohemorrhagic and enteroinvasive E coli, Yersinia enterocolitica, Clostridium difficile, Entamoeba histolytica, and Salmonella and Shigella species.
In some types of food poisoning (eg, staphylococci, B cereus), vomiting is caused by a toxin acting on the central nervous system. The clinical syndrome of botulism results from the inhibition of acetylcholine release in nerve endings by the botulinum.
The pathophysiological mechanisms that result in acute GI symptoms produced by some of the noninfectious causes of food poisoning (naturally occurring substances [eg, mushrooms, toadstools] and heavy metals [eg, arsenic, mercury, lead]) are not well known.
A major contributor to seafood contamination with foodborne pathogens appears to be naturally occurring biofilm formation.  Vibro and Salmonella species, Aeromonas hydrophila, and Listeria monocytogenes are common seafood bacterial pathogens that form biofilms.
Initially, food-borne diseases were estimated to be responsible for 6-8 million illnesses and as many as 9000 deaths each year. [5, 6] However, the change in food supply, the identification of new food-borne diseases, and the availability of new surveillance data have changed the morbidity and mortality figures. The US Centers for Disease Control and Prevention (CDC) estimates 1 in 6 Americans (48 million people) are affected by foodborne illness annually. The estimates suggest 128,000 people are hospitalized and 3,000 die.  The 31 known pathogens account for an estimated 9.4 million annual cases, 55,961 hospitalizations, and 1,351 deaths. Unspecified agents account for 38.4 million cases, 71,878 hospitalizations, and 1,686 deaths. 
Overall, food-borne diseases appear to cause more illnesses but fewer deaths than previously estimated. 
In a 2013 report, CDC investigators used data spanning the decade between 1998 and 2008 to report estimates for annual US food-borne illnesses, hospitalizations, and deaths attributable to each of 17 food categories. [10, 11] The following were among their findings [10, 11] :
Leafy green vegetables were the most common cause of food poisoning (22%), primarily due to Norovirus species, followed by E coli O157.
Poultry was the most common cause of death from food poisoning (19%), with Listeria and Salmonella species being the main infectious organisms.
Dairy items were the second most frequent causes of foodborne illnesses (14%) and deaths (10%), with the main factors being contamination by Norovirus from food handlers and improper pasteurization resulting in contamination with Campylobacter species.
In March 2012, the CDC reported a rise in foodborne disease outbreaks caused by imported food in 2009 and 2011. Nearly 50% of the outbreaks implicated food that was imported from regions not previously associated with outbreaks. Outbreaks reported to CDC’s Foodborne Disease Outbreak Surveillance System from 2005-2010 implicated 39 outbreaks and 2,348 illnesses that were linked to imported food from 15 countries. Within this 5-year period, nearly half (17) occurred in 2009 and 2010. Fish (17 outbreaks) was the most common source of implicated imported foodborne disease outbreaks, followed by spices (6 outbreaks including 5 from fresh or dried peppers). Approximately 45% of the imported foods causing outbreaks came from Asia. 
The CDC recognized the following outbreaks and sources in 2012  :
E coli – Spinach and spring mix, raw clover sprouts at a national chain of restaurants
Salmonella – Peanut butter, ricotta salata cheese, mangoes, cantaloupe, ground beef, live poultry, dry dog food, raw scraped ground tuna product, small turtles, raw clover sprouts
Transnational trade; travel; and migration and globalization of food production, manufacturing, and marketing pose greater risk of cross-border transmission of infectious diseases and food-borne illness.  A travel history should be obtained because traveler's diarrhea is the leading cause of travel-related illness. Onset occurs 3 days to 2 weeks after arrival. Illness is self-limiting within 5 days. Enterotoxigenic E coli is the most common isolate.
Symptoms vary in degree and combination. These may include abdominal pain, vomiting, diarrhea, headache, and prostration. More serious cases can result in life-threatening neurologic, hepatic, and renal syndromes leading to permanent disability or death.
Morbidity and mortality are higher in elderly individuals. The reasons for this increased susceptibility in elderly populations include age-associated decrease in immunity, decreased production of gastric acid and intestinal motility, malnutrition, lack of exercise, habitation in a nursing home, and excessive use of antibiotics. Elderly persons are more likely to die from infection with C perfringens; E coli O157; and Salmonella, Campylobacter, and Staphylococcus organisms.
The CDC found that 5 bacterial enteric pathogens (Campylobacter, E coli 0157 , Salmonella, Shigella, and Y enterocolitica) caused 291,162 illnesses annually in children younger than 5 years.  This resulted in 102,746 doctor visits, 7,830 hospitalizations, and 64 deaths. Rates of illness remain higher in children.
Complications are very rare in healthy hosts, except in cases of botulism or mushroom poisoning. Infants, elderly people, and immunocompromised hosts are more susceptible to complications. Other complications include the following:
Guillain-Barré syndrome ( Campylobacter infection)
Hemolytic uremic syndrome ( E coli O157:H7)
Irritable bowel symptoms may follow acute gastroenteritis.
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