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7/28/2019 Lab Diagnosis of Diarrheal Diseases
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Lab diagnosisof Diarrhealdiseases
Dr.TanmayMehta
Ahmedabad
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Epidemiology
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Diarrheal diseases in developing countriescause death of children
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Endemic infections
High frequency in children is related tofecaloral spread and lack of immunity
Geographic distributions change
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Epidemic infections
Typhoid, cholera, and shigellosis spreadwhere hygiene is poor or after majordisasters
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definitions
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Diarrheal diseases includes
Diarrhea
DysenteryGastroenteritis , Food poisoning
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Diarrhea : WHO definition
Frequency > 3 times a day
Consistency is looser than usual
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Dysentery
Stool + mucous + blood
It can be
Bacillary: Shigella (MC)
Amoebic : E.histolytica(MC)
Sigmoidoscopy : inflammed and
engorged mucosa of largeintestine in bacillary dysentery
Inflammation, cytotoxins, or
invasion produce pus and blood
Colon is primary location
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-itis = inflammation
Gastroenteritis = inflammation of g.i. tract(stomach + inestine) due to infection withbacteria and viruses
Acute
Chronic
Enterocolitis = inflammoation of lower g.i.t.
(intestine + colon) without involvingstomach
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Food Poisoning
Acute Gastroenteritis
Caused By ingestion of
single meal contaminated by large no. ofbacteria or preformed bacterial toxin
Nonbacterial causes
Mushroom
chemicals
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Food poisoning (c0nt.)
Single-source outbreaks are becoming largerwith modern food processing anddistribution
Diseases from ingestion of preformed toxinhave short incubation periods
Infection is associated with impropercooking and/or storage
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Classification of diarrheal
diseases-Noninfective : e.g., UC-Infective
-Bacterial-Nonbacterial
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Infective diarrheal diseases
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Modes of transmission:
Feco-oral transmission:
Person to person
Food contamination before,during&afterprocessing
Drinking Water contamination
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Etiological agent
Clinical syndromes overlap for
specific etiologic agents
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Etiology of Infective Diarrhea
Noninvasive bacteria (toxin)
V.cholera (CT)
EPEC (LT)
EHEC (VT) Cl.perfringens A
Staph. Aureus
Bacillus cereus
Shigella dysenteriae-1
Vibrio parahemolyticus
Invasie bacteria (nontoxin)
Salmonella
Campylobacter
Shigella EIEC
EHEC
Yersinia enterocolitica
Yersiniapseudotuberculosis
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Etiology of food poisoning
Intoxication
B.cereus -V(IP=1-6 h)
Rewarmed fried rice
S.aureus (IP=2-4 h) Meat , custords , salads
C.botulinum (12-72 h)
Canned food
V.parahemolyticus (10-24h) Shell fish
Infection
B.cereus-D (6-12 h)
Meat , poultry , vegetables
C.perfringens (9-15 h) Meat , poultry
Salmonella (6-48h)
Poultry , eggs , meat ,
vegetables Shigella (12-48 h)
Variable
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Non bacterial causes
Viruses
Rotavirus (MC)
Norwalk virus
Noro virus
Adeno virus
Astrovirus
Parasites
C.parvum
Giardia lamblia
E.histolytica
Fungi
candida
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Hospital-associated Diarrhea
E. coli, C. difficile, and rotaviruses can causehospital outbreaks
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Travelers Diarrhea
Visits to developing countries are frequentlymarred
ETEC is the predominant cause of travelers
diarrhea
Travelers should avoid salads and otheruncooked foods
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Pathogenesis
Invasive
Invasion ofintestinalmucosa by celldestruction
Toxin mediated
Enterotoxins : CT of V.cholerae ,LT of E.coli
Subunit B : binding to intestinal epithelium
Subunit A : activates adenyl cyclase : increase CAMP
Cytotoxin : VTEC & Shiga toxin
Bloody diarrhea
HUS =ARF + thrombocytopenia + hemolytic anemia
Multiplication of bacteria in GIT
Adherence (colonisation) by fimbriae and other proteins : adherence preventsnormal function of absorption and secretion
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Clinical features
Frequency of stools
Nausea , vomiting
Abdominal pain , fever Cramps
Dehydration : Dry mouth , low BP
Electrolyte imbalance
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Lab diagnosis
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Specimen collection
Stool sample
Vomitus material
Food sample Blood
Rice watery stool sample of cholera
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Microscopy
Gram stain : Gram negative and positive Bacteria
Saline & Iodine preparation : for cysts and eggs ofparasites
Acid fast stain : for Bacteria and parasites Electron microscopy detects rotaviruses
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Gram negative S shaped and gull wing shapedCampylobacter jejuni
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Acid fast stain : C.parvum
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Culture
Stool culture requires selective media forcommon agents
MacConkey agar LF colonies
Dry Mucoid
NLF colonies
TCBS for suspected cholera Blood agar & RCM for food poisoning cases Blood cultures are positive in early stages of
enteric fever
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TCBS : Yellow coloniesof V.cholerae
MacConkey : LF colonies
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Identification of organisms
Biochemical reactions
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Toxin assays
Detection of toxin in supected food and inpatients serum in food poisoning cases
Cell culture or antigen assays detect C.difficile toxin
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Antibiotic sensitivity
To decide specific therapy against identifiedorgansim
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Ag-Ab reactions
Serology is generally ancillary
Antigen detection available for a rotaviruses
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Moral of the story is
Diarrheal diseases in developing countriescause death of children
Fluid loss from proximal small intestine is theprimary mechanism
Maintenance of fluid and electrolyte balancealways important
Antimicrobic therapy is primarily for invasivedisease
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THANKS