The salient facts about food poisoning

Food poisoning is an acute illness, usually of sudden onset, brought about by consuming poisonous food or food and water contaminated with bacteria and/or their toxins, or with parasites, viruses, or chemicals.  

The most common pathogens involved in foodborne infections are NorovirusSalmonella sp., Shigella dysenteriae, Campylobacter jejuni, Clostridium perfringens, Escherichia coli, Yersinia enterocolitica, Listeria monocytogenes and Vibrio parahaemolyticus. The symptoms of food poisoning normally include abdominal pain, diarrhoea, nausea, vomiting and fever. 

Bacterial food poisonings are of two types: infection and intoxication. Infections are caused by the presence of ingested viable, usually multiplying microorganisms at the site of inflammation.  

However, intoxications are strictly poisonings due to toxins produced by microorganisms in the ingested food. Common bacteria involved in intoxications are Staphylococcus aureus, Bacillus cereus and Clostridium botulinum.  

Intoxications and enterotoxins (toxins released after ingestion of contaminated food) in the gut are associated with non-inflammatory diarrhea characterized by large volume watery diarrhea in the absence of blood, pus, or severe abdominal pain. Occasionally, profound dehydration may result.  

Inflammatory diarrhea is caused by the action of cytotoxins on the mucosa, commonly of colon or the distal small bowel which then promote invasion and destruction of gut mucosa. The diarrhea usually is bloody; mucoid and leukocytes are present. Patients are usually febrile. Dehydration is less likely than with noninflammatory diarrhea because of smaller stool volumes. Examples of these pathogens include Campylobacter jejuni, Vibrio sp, enterohemorrhagic and enteroinvasive E coli, Yersinia enterocolitica, Clostridium difficile, Entamoeba histolytica, and Salmonella and Shigella species. 

Information about the length of time between eating the food and the beginning of symptoms can help in diagnosing the problem: Less than six hours suggests that the infection was caused by a type of bacterium that creates a toxin in the food before it was eaten (such as staphylococcus); Twelve hours or more suggests the infection was caused by enterotoxic bacteria (such as certain types of E. coli), or a bacterium, virus or parasite that can damage the cells lining the intestine (such as salmonella) 

Abdominal pain is most severe in inflammatory processes. Painful abdominal cramps suggest underlying electrolyte loss, as in severe cholera.  

When vomiting is the major presenting symptom, suspect Staphylococcus aureus, B cereus, or Norovirus. 

Reactive arthritis can be seen with Salmonella, Shigella, Campylobacter, and Yersinia infections, which can over time develop into chronic arthritis. 

A history of bloating should raise the suspicion of giardiasis. 

A profuse rice-water stool suggests cholera or a similar process. 

Yersinia enterocolitis may mimic the symptoms of appendicitis. 

Proctitis syndrome characterized by tenesmus and frequent painful bowel movements containing blood, pus, and mucus is seen with shigellosis. 


The main objective in managing patients with food poisoning is adequate rehydration and electrolyte replacement, which can be achieved with either an oral rehydration solution or intravenous solutions (eg, isotonic sodium chloride solution, lactated Ringer solution) in severely dehydrated individuals or those with intractable vomiting.  

Use of antidiarrheal medications, including antimotility agents (diphenoxylate, loperamide), anticholinergics (atropine), and adsorbents, is not recommended in children, especially those younger than two years, or in patients with fever, systemic toxicity, or bloody diarrhea or in patients whose condition either shows no improvement or deteriorates, because they may increase the risk of invasive disease. 

Symptomatic treatment with antisecretory agents (eg, bismuth subsalicylate) and antiperistaltics [eg diphenoxylate with atropine (lomotil), loperamide (imodium)] may be considered in adults with uncomplicated acute or traveler’s diarrhea. 

In patients with clinically significant vomiting, antiemetics should be considered.  A single dose of ondansetron is recommended in children. 

Antibiotic therapy can shorten the duration of symptoms and may prevent bacteremia in older adults, newborns, and immunocompromised patients. However, most acute diarrheal infectious are viral, and improper use of empiric antibiotics is associated with increased morbidity (eg, increased risk of hemolytic uremic syndrome by shiga toxin-like E coli) and superinfection with Clostridium difficile.  

Thus, in the absence of dysentery, do not administer antibiotics until a microbiologic diagnosis is confirmed and Shiga toxin–producing E coli O157:H7 is ruled out. 

Empiric antibiotics (generally, fluoroquinolone or trimethoprim/sulfamethoxazole in children and a macrolide, such as erythromycin and azithromycin in areas where Campylobacter jejuni is present) should be considered in the presence of fever, and signs of invasive disease (e.g., gross hematochezia, leukocytes on fecal smear); if symptoms have persisted for more than one week or are severe (i.e., more than eight liquid stools per day), or if hospitalization may be required.  

Enterotoxigenic E. coli is the most common cause of traveler’s diarrhea worldwide and is generally susceptible to ciprofloxacin or TMP/SMX. 

Infection with either V cholerae or V parahaemolyticus can be treated either with a fluoroquinolone or with doxycycline. 

Shigella can be managed with a 3-day course of ciprofloxacin or 5 days of Azithromycin (Children, TMP-SMX or Azithromycin). 

Patients with fatty or foul-smelling stools, cramps, bloating, and weight loss can be treated empirically for Giardia infection with Metronidazole. 

Probiotics (Lactobacillus and Saccharomyces: live “good” bacteria and yeasts) may also be helpful in treating gastroenteritis. One study found that the use of probiotics in children for acute gastroenteritis shortened their hospital stay by an average of 1.12 days.  

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. 

If a stool sample shows positive results for WBCs or blood or if patients have fever or symptoms persisting for longer than 3-4 days, stool and blood culture should commenced. 

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 


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