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Infectious Disease And Microbiology – Food-Borne Diseases
Food-borne diseases are illnesses that result from ingestion of food contaminated by pathogenic microorganisms, microbial toxins, or chemical substances. They are extremely common and represent a major public health problem. In the United States alone, it has been estimated that more than 75 million episodes occur annually. Outbreaks are most often caused by noroviruses, followed by Salmonella. Infants, older adults, and immunocompromised individuals are at particularly high risk for severe disease. Some pathogens also have specific risk groups; for example, Vibrio vulnificus infection is more common and more severe in patients with chronic liver disease or other forms of immunosuppression.
Prevention is centered on safe food handling and avoidance of high-risk foods. Raw or undercooked eggs, unpasteurized dairy products, raw or undercooked meat, poultry, and seafood, as well as soft cheeses, should be avoided when possible. Cross-contamination during food preparation should be prevented, and handwashing before handling food is essential. Vaccination also plays a role in prevention, particularly hepatitis A immunization and infant vaccination against rotavirus.
The causes of food-borne illness are broad and include bacterial, viral, parasitic, and noninfectious toxins. Bacterial causes include Salmonella, Shigella, enterohemorrhagic and enterotoxigenic Escherichia coli, Campylobacter jejuni, Vibrio species, Yersinia species, Clostridium perfringens, Staphylococcus aureus, Bacillus cereus, Clostridium botulinum, and Listeria monocytogenes. These organisms are associated with particular foods such as poultry, eggs, shellfish, contaminated water, undercooked beef, rice, canned foods, and unpasteurized dairy products. Viral agents include norovirus, rotavirus, and hepatitis A virus, while parasites include Giardia lamblia, Entamoeba histolytica, Cryptosporidium, and Cyclospora cayetanensis. Noninfectious causes include marine toxins such as ciguatera toxin, scombroid toxin, tetrodotoxin, shellfish toxins, as well as heavy metals, mushroom toxins, pesticides, and certain food additives such as monosodium glutamate.
The clinical presentation depends on the causative agent. Bacterial infections often present with diarrhea, abdominal cramps, fever, nausea, and vomiting, although the exact pattern varies. Salmonella commonly causes diarrhea, fever, and cramps, while Shigella often produces bloody, mucus-containing stools. Enterohemorrhagic E. coli typically causes severe abdominal pain and bloody diarrhea with little or no fever. Campylobacter may cause bloody diarrhea and fever, while cholera presents with profuse watery diarrhea leading to dehydration. Preformed toxin illnesses such as those caused by Staphylococcus aureus and the emetic type of Bacillus cereus produce abrupt, intense vomiting within hours of ingestion. Clostridium botulinum causes gastrointestinal symptoms followed by neurologic signs such as blurred vision, diplopia, dysphagia, and descending paralysis.
Viral food-borne diseases commonly cause acute gastroenteritis. Norovirus produces nausea, vomiting, cramping, diarrhea, low-grade fever, and myalgias, with vomiting more common in children and diarrhea more common in adults. Rotavirus causes vomiting and watery diarrhea, especially in young children. Hepatitis A has a much longer incubation period and presents with jaundice, dark urine, flu-like symptoms, and sometimes diarrhea.
Parasitic infections tend to have more prolonged courses. Giardia causes diarrhea, gas, and abdominal cramps that may last weeks to months. Entamoeba histolytica often causes bloody diarrhea and lower abdominal pain. Cryptosporidium usually causes watery diarrhea and cramps, while Cyclospora often causes prolonged watery diarrhea with nausea, anorexia, and weight loss.
Noninfectious food-borne toxins often produce rapid symptom onset. Ciguatera poisoning causes gastrointestinal symptoms followed by neurologic manifestations such as paresthesias and reversal of hot and cold sensation, and sometimes cardiovascular effects such as bradycardia and hypotension. Scombroid poisoning causes flushing, rash, urticaria, dizziness, and paresthesias shortly after eating affected fish. Tetrodotoxin from puffer fish causes rapid neurologic symptoms, ascending paralysis, and respiratory failure. Shellfish toxins may cause diarrheal, neurotoxic, amnesic, or paralytic syndromes depending on the toxin involved.
Physical examination usually focuses on assessing dehydration and abdominal findings. Signs such as dry mucous membranes, reduced urine output, tachycardia, and hypotension suggest volume depletion. Abdominal tenderness may be present. In Vibrio vulnificus infection, bullous skin lesions may occur.
Diagnosis depends on the suspected cause. Stool culture is useful for Salmonella, Shigella, Campylobacter, certain E. coli strains, Vibrio, and Yersinia, although special media are needed for some of these organisms. Clostridium botulinum diagnosis relies on testing stool, serum, or food for toxin. Viral illnesses such as norovirus are often diagnosed clinically, while rotavirus can be identified by stool immunoassay and hepatitis A by positive IgM antibody. Parasitic infections are diagnosed by stool examination for ova, cysts, or parasites, or by enzyme immunoassays. Toxin-mediated illnesses may require toxin assays, chromatography, or histamine detection in food.
Treatment for most food-borne illnesses is supportive, with fluid and electrolyte replacement as the mainstay. Specific antimicrobial therapy is reserved for selected infections. Typhoid fever caused by Salmonella typhi or S. paratyphi may be treated with cefixime, ceftriaxone, or quinolones, although resistance is an issue in some regions. Severe enterotoxigenic E. coli and Campylobacter infections may be treated with antibiotics. Cholera requires aggressive rehydration plus doxycycline or tetracycline in adults, or trimethoprim-sulfamethoxazole in young children. Botulism requires prompt antitoxin administration, with botulism immune globulin used in infants. Serious Listeria infections are treated with ampicillin, sometimes combined with gentamicin. Parasitic infections are treated with agents such as metronidazole, nitazoxanide, or trimethoprim-sulfamethoxazole depending on the organism. Noninfectious toxin syndromes are managed supportively, though antihistamines may help in scombroid poisoning and intravenous mannitol has been used for ciguatera.
The prognosis is generally good for most uncomplicated food-borne illnesses, though immunocompromised individuals may have prolonged disease and prolonged shedding of pathogens. Some conditions are life-threatening, especially cholera because of severe dehydration, and tetrodotoxin or paralytic shellfish toxin poisoning because of respiratory paralysis. Complications may also occur, such as temporary lactose intolerance after rotavirus infection, and reactive arthritis or Guillain–Barré syndrome after Campylobacter jejuni infection.
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