23 - Food poisoning - Diagnosis

• Short incubation (ie, within 1 d, usually less than16 h)
  
  • Chemical causes (ultrashort incubation): The onset of nausea, vomiting, and cramps within 1-2 hours is observed in poisonings involving metal, fish-associated toxins (eg, scombroid, ciguatera), shellfish-associated toxins, monosodium glutamate, or mushrooms. The toxic agent in shellfish-related and ciguatera-related disease is derived from dinoflagellate organisms present in the fish or shellfish. Note that neurologic symptoms can present weeks later. Amanita mushrooms can lead to hepatorenal failure.
  • Bacterial causes - Emetic syndrome (1-6 h)
    
    • S aureus: Nausea and vomiting are caused by the action of preformed enterotoxins A-E.
    • Bacillus cereus (emetic syndrome, indistinguishable from staphylococcal food poisoning): This spore-forming rod is present in raw rice grains. The emetic toxin is a preformed heat-stable toxin produced upon germination of the spores.
    
    
  • Bacterial causes - Diarrheal syndrome (8-16 h)
    
    • B cereus (diarrheal syndrome): The diarrheal toxin is a heat-labile toxin formed after sporulation.
    • Clostridium perfringens type A: Diarrhea and abdominal cramps occur within 1 day of ingestion of cooked meat stored at 15-60°C. Slow cooling allows heat-activated spores to germinate and to elaborate the enterotoxin.
    
    
  
  
• Intermediate incubation (1-3 d)
  
  • Diarrheal disease: This category comprises bacterial and viral infectious pathogens. The clinical presentation depends on the target organ (ie, small bowel or large bowel), which varies depending on the pathogen.
  • Diarrheal disease, large bowel enteritis: Fever and constitutional symptoms usually accompany the diarrhea caused by invasive pathogens in the large bowel. Dysentery, bloody stools with mucous, and cramps or tenesmus are typical.
    
    • Campylobacter jejuni: This is a leading cause of bacterial food-borne illness in the United States. Vomiting is uncommon, and the illness is short and self-limiting.
    • Shigella species: Shigellae cause the prototypical diarrheal syndrome with blood, mucous, and pain that is termed bacillary dysentery. Tenesmus and small-volume stools are typical. Toxemia may be severe, occasionally causing seizures in children.
    • Enteroinvasive E coli (EIEC): Several serotypes of diarrheagenic E coli possess Shigella -like invasiveness factors that allow mucosal invasion. The disease is a febrile dysentery that mimics shigellosis.
    • Salmonella species, nontyphoidal salmonellosis: This is a zoonotic infection acquired from bovine or poultry reservoirs and is very common in the United States. The illness can range from mild nonbloody diarrhea to a severe dysenteric illness.
    • Salmonella species, enteric (typhoid) fever: In the United States, enteric fever occurs in travelers or recent immigrants and is a systemic toxic illness. Salmonella typhi has an exclusively human reservoir and is acquired either via ingestion of a large inoculum in food or contaminated water or from personal contact with a carrier.
    • Vibrio parahaemolyticus: Although it is a common worldwide pathogen, in the United States, V parahaemolyticus infection is restricted geographically to the Atlantic and Gulf coasts. The diarrhea is profuse and watery, and blood is not commonly present in the stool.
    
    
  • Diarrheal disease, small bowel enteritis
    
    • Enterotoxigenic E coli (ETEC): Enterotoxin-producing strains of E coli are the most common cause of traveler's diarrhea. The diagnosis is clinical; fever and bloody stools are typically absent.
    • Vibrio cholerae (01 and non-01 strains): Cholera is likely only in endemic areas and during epidemics. The profuse diarrhea and vomiting can lead to dehydration and prostration.
    • Viral agents (Norwalklike viruses, rotavirus, adenoviruses, astroviruses, caliciviruses): Vomiting and headache accompany the diarrhea and fever more commonly with viral than with bacterial infections.
    • All the large bowel pathogens also secrete enterotoxins that induce profuse watery small bowel diarrhea in some patients.
    
    
  • Botulism: Nausea, vomiting, skeletal muscle paralysis, and autonomic symptoms occur within 18-36 hours of ingestion of food containing Clostridium botulinum. The disease is mediated by preformed toxin in older children and adults, but it may follow ingestion of spores in infants. Diarrhea occurs only in approximately 5% of patients; instead, constipation may be noted. Infants with botulism present with muscular weakness that manifests as weak cry, difficulty sucking and swallowing, or respiratory failure. Upon examination, the baby has profound hypotonia but may be alert.
  
  
• Long incubation (3-5 d)
  
  • Enterohemorrhagic E coli (EHEC): These strains of E coli cause hemorrhagic colitis with a 15% risk of progression to hemolytic-uremic syndrome (HUS) in children, which is the result of cytotoxins termed verotoxins or Shigalike toxins. E coli O157:H7 is one of many such cytotoxin-producing E coli strains that reside in the gut of cattle. Although these organisms can cause mild nonbloody diarrhea, hemorrhagic colitis is the usual symptom. Mild abdominal pain, malaise, and transient fever are followed by watery diarrhea. Bloody stools and more severe abdominal pain ensue several days later. Paucity of fever is a diagnostic clue. When HUS occurs, its onset is 5-13 days after the onset of diarrhea.
  • Yersinia species
    
    • Yersinia enterocolitica most often causes a febrile illness with abdominal pain due to mesenteric lymphadenitis in which diarrhea is not prominent. The illness can mimic appendicitis. The illness may be prolonged, lasting 2-3 weeks. In infants, a diarrheal illness is common, with occasional septicemia. The diagnosis is made with blood and stool cultures. Treatment is indicated only for infants with septicemia.
    • The symptom complex for Yersinia pseudotuberculosis infection includes fever, rash (scarlatiniform or erythema nodosum), and abdominal pain.
    
    
  
  
• Very long incubation (1-4 wk): This category comprises parasitic food-borne diseases (FBDs), but shorter incubation periods can occur, especially in Entamoeba histolytica infection.
  
  • Parasitic
    
    • Giardiasis: The spectrum of illness ranges from asymptomatic carriage to acute watery diarrhea, but a subacute intermittent diarrheal illness is also common.
    • Amebiasis: E histolytica is a protozoan that causes dysentery and extraintestinal, most commonly hepatic, abscesses.
    • Cryptosporidiosis: The organism Cryptosporidium parvum causes a diarrheal illness with fever and abdominal pain.
    • Cyclosporiasis: Frequent watery stools, which can be accompanied by fever and a relapsing course, characterize this FBD caused by Cyclospora cayetanensis.
    • Trichinosis: This is a rare illness, caused by Trichinella spiralis, that is acquired by ingestion of contaminated or raw pork, bear, or moose meat. GI tract symptoms are followed by muscle inflammation and periorbital edema.
    • Cysticercosis: This infection is caused by the larval stage of pork tapeworm and is most often acquired by ingestion of food or water contaminated with the ova of the tapeworm rather than from eating raw pork.
    • Anisakiasis, fish tapeworm, and flatworm infections: These uncommon worm infestations occur after consumption of certain types of raw fish.
    
    
  • Bacterial
    
    • Listeriosis: Diarrhea in Listeria monocytogenes infection may be mild, but systemic symptoms are prominent. The diarrhea has a short incubation period (<48 h), but symptoms of systemic spread could appear weeks later. The major risk is that of maternal infection during pregnancy. Neonatal sepsis and meningitis follow amniotic fluid infection. Older children and adults can develop meningitis. The infection is a particular hazard to individuals who are immunocompromised.
    • Brucellosis: This is a febrile illness now only rarely acquired in the United States. The food source is raw or unpasteurized milk or cheese, most commonly from goats (Brucella melitensis).
    
    
  • Viral: The incubation period of hepatitis A is 15-50 days for this viral hepatitis transmitted via the fecal-oral route.
  • Protozoal, toxoplasmosis: A febrile and subacute lymphadenitis results from ingestion of undercooked meat. A nonspecific illness with systemic symptoms and generalized lymphadenopathy can occur in healthy individuals, or an asymptomatic infection can result. Persons who are immunocompromised can develop CNS infection.
  
  

12 - Facultative anaerobes part 2 ( ENTEROBACTERIACEAE )

• Salmonella :

o 2000 serotypes based on H (flagella protein), O (outer membrane protein) & K (Capsular protein)

o Antibodies obtained commercially for serotyping using Kauffmann-White scheme.

o Some Salmonella serotypes are host specific (humans= S. typhi S. paratyphi; animals (S. cholerae-suis but cause severe disease if transmitted to humans) & some others not host specific (affect humans & animals)

o Food borne disease mainly thro' poultry, eggs & dairy products

o Exposure to Salmonella is frequent but requires a high dose of 1 to 100 million (eg improperly refrigerated foods; low dose for immunocompromised, very young and the elderly or with decreased gastric acidity

o Disease is due to microbial growth in body tisssue & not by ingestion of foods contaminated with toxins as a result of microbial growth

o Salmonella infections occurs in one of four forms:

 Gastoeneteritis (S. enteritis) most common form; eating contaminated foods; elevated temperatures, cramps & head ache. Symptoms disappear spontaneously in 2 to 7 days
 Septicimia--All Salmonella can cause bacterimia (S. cholera-suis, S. typhi & S. paratyphi)
 Enetric fever (S. typhi- typhoid fever & S. paratyphi- paratyphoid fever)-- Similar symptoms but paratyphoid fever milder; Transmission by consumption of contaminated foods --> multiplication in intestine (endothelial cells)--> invades lymphatic tissues to blood stream & kidneys (excreted in urine)
 Asymptomatic carriage-- Establishes in gall bladder (ressists bile & bile salts); continuous feedback into intestine; known as carrier state (2-5% typhoid patients become carriers & excrete 1 to 1000 million S. typhi /gm feces & also in urine); Carrier state is important in transmission of the disease. Mary Mallon (1901), aka Typhoid Mary, was the first carrier case to be detected; In 15 years infected 200 & jailed to prevent spred of typhoid fever. Disease has declined due to curative & preventative measures (heat killed injectable vaccines or the new live oral vacciine; same efficacy but later has less side effects


• Shigella : 

o Simple taxonomy (4 species & 32 serotypes) unlike Salmonella

o Found in humans, apes & monkey only unlike Salmonella

o Cause bacillary dysentry (shigellosis); S. sonnei (industrialized nations) & S. flexneri (developing nations); S. sonnei mild but S. dysenteriae (aka Shiga bacillus produces Shiga toxin) severe.

o Shigella enter endothelial cells (intestine) & multiply causing tissue damage; exotoxins stop host cell protein synthesis. Rarely (with the exception of S. dysenteriae) cause septicimia. 20 bowel motions a day.

o Transmission by fecal-oral route thro' contaminated hands & usually not by food-water

o Low dose required-- 200 Shigella cells can establish disease

11 - Facultative anaerobes part 1 ( ENTEROBACTERIACEAE )

• Produce acid & gas anaerobically
• Medically very important
• 3 families:
o ENTEROBACTERIACEAE (peritrichous)
o VIBRIONACEAE (polar)
o PASTEURELLACEAE (none)
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ENTEROBACTERIACEAE : 

General comments - 
 
• Most important heterogenous collection of medically significant bacteria (27genera & 110 sp)
 
• Ubiquitous- soil, water, vegetation (saprophytes) & some normal flora of humans & animals but opportunistic (E.coli, Klebsiella pneumoniae, Proteus mirabilis) and some always pathogenic (Salmonella, Shigella & Yersinia pestis).
 
• Infections can originate from an animal reservoir (Salmonella), from a human carrier (S. typhi, Shigella) or by endogenous spread of the organism in a suspetible patient (E. coli)
 
• Readily culturable on non-selective media from sterile specimens (spinal fluid, tissues), selective media eosin methylene blue (EMB), MacConkey agar for contaminated specimens (sputum, feces), highly selective media (eg stool samples-- normal flora mask) & cold enrichment technique (stool sample + saline --> 4 C / 2 weeks; most enerobacters killed but not Yersinia enterocolitica (slow grower)
 
• Identification based on fermentation products (types & ratio) eg Butanediol (Enterobacter); mixed acids (E. coli; Salmonella & Shigella-- ratios of products important) , serological properties but cross-reactions limit usefulness [flagella (H), lipopolysaccaharide (O) & capsular (K); eg E.coli (170H, 56H & numerous K), biochemical propeties identification within 4 to 24 hrs; Capsules-- Klebsiella
 
• Treatment with antibiotics (E. coli, Proteus miabilis) but some highly ressistant & in some cases not recommended (S. enteriditis, prolongs carrier state). Antibiotic ressistant bacterial infections commonly hospital acquired (not community aquired)
 
• Pathogenecity : 
 
• Endotoxins (lipid A of LPS) released from cell lysis , flagella, pilli & fimbrae in adherence & attachment; capsules --weakly antigenic & protect against antibody mediated phagocytosis