Lab Diagnosis of Diarrheal Diseases

7/28/2019 Lab Diagnosis of Diarrheal Diseases

1/37

Lab diagnosisof Diarrhealdiseases

Dr.TanmayMehta

Ahmedabad


2/37

Epidemiology


3/37

Diarrheal diseases in developing countriescause death of children


4/37

Endemic infections

High frequency in children is related tofecaloral spread and lack of immunity

Geographic distributions change


5/37

Epidemic infections

Typhoid, cholera, and shigellosis spreadwhere hygiene is poor or after majordisasters


6/37

definitions


7/37

Diarrheal diseases includes

Diarrhea

DysenteryGastroenteritis , Food poisoning


8/37

Diarrhea : WHO definition

Frequency > 3 times a day

Consistency is looser than usual


9/37

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


10/37

-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


11/37

Food Poisoning

Acute Gastroenteritis

Caused By ingestion of

single meal contaminated by large no. ofbacteria or preformed bacterial toxin

Nonbacterial causes

Mushroom

chemicals


12/37

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


13/37

Classification of diarrheal

diseases-Noninfective : e.g., UC-Infective

-Bacterial-Nonbacterial


14/37

Infective diarrheal diseases


15/37

Modes of transmission:

Feco-oral transmission:

Person to person

Food contamination before,during&afterprocessing

Drinking Water contamination


16/37

Etiological agent

Clinical syndromes overlap for

specific etiologic agents


17/37

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


18/37

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


19/37

Non bacterial causes

Viruses

Rotavirus (MC)

Norwalk virus

Noro virus

Adeno virus

Astrovirus

Parasites

C.parvum

Giardia lamblia

E.histolytica

Fungi

candida


20/37

Hospital-associated Diarrhea

E. coli, C. difficile, and rotaviruses can causehospital outbreaks


21/37

Travelers Diarrhea

Visits to developing countries are frequentlymarred

ETEC is the predominant cause of travelers

diarrhea

Travelers should avoid salads and otheruncooked foods


22/37

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


23/37

Clinical features

Frequency of stools

Nausea , vomiting

Abdominal pain , fever Cramps

Dehydration : Dry mouth , low BP

Electrolyte imbalance


24/37

Lab diagnosis


25/37

Specimen collection

Stool sample

Vomitus material

Food sample Blood

Rice watery stool sample of cholera


26/37

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


27/37

Gram negative S shaped and gull wing shapedCampylobacter jejuni


28/37


29/37

Acid fast stain : C.parvum


30/37

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


31/37

TCBS : Yellow coloniesof V.cholerae

MacConkey : LF colonies


32/37

Identification of organisms

Biochemical reactions


33/37

Toxin assays

Detection of toxin in supected food and inpatients serum in food poisoning cases

Cell culture or antigen assays detect C.difficile toxin


34/37

Antibiotic sensitivity

To decide specific therapy against identifiedorgansim


35/37

Ag-Ab reactions

Serology is generally ancillary

Antigen detection available for a rotaviruses


36/37

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


37/37

THANKS

Documents

Lab Diagnosis of Diarrheal Diseases