Typhoid fever



Pathogenesis of typhoid fever:

[A]Causative agent:Salmonella typhi.

[B]Route of transmission:Faeco-oral route(from food,water,ice cream etc)

[C]Incubation period:10-14 days.


Entry of salmonella typhi to the stomach.

Duodenum(Small intestine)

Mesentric lymph nodse (Multiply)Via thoracic duct.

Enter blood (Primary bacteraemia)

Multiply in liver,spleen,bone marrow,kidney,lung.

Pass into blood causing secondary baxtermia(Onset of fever & other signs of clinical illness-Typhoid fever)

Gall bladder,liver,spleen(2nd & 3ed week)

Peyer’s patches of intestine.

Lymphatics follicles(Necrosis & Sloughing).

Typhoid fever/Ulcer(4th & 5th weeks)

Lab diagnosis of Typhoid fever:                       

[A]Principle:Diagnosis is based on isolation of salmonella typhi by blood culture and antigen.Perference of diagnosis defer according to duration of fever.


(A)Specimen collection:

  1. a) Blood:For culture (1st week).
  2. b) Serum:For widal test (2nd week).
  3. c) Stool:For culture (2nd & 3rd week).
  4. d) Urine:For urine culture (4th week).

(B)Microscopic examination:It is not helpful.

  1. a) WBC count may be normal or low.
  2. b) Raised ESR.

(C)Isolation & Identification(Culture):

Blood culture:Mostly reliable in 1st week can be done in 3 processess:

a) Rapid culture system(Examined after 24 hours).

b) Trypticase soy broth(Blood is collected before starting specific antibiotic).

c) Automated method(Solid media are used very rapid with in 6 hour)

Stool culture:Positive for 2nd or 3rd week.It is done in at least 2 solid media (e.g Macconkey agar deoxycholate citrate agar etc) and 1 liquid media (e.g Tetrathionate broth).

Urine culture:Positive in 2nd,3rd & 4th week,culture is done   in- Macconkey agar deoxycholate citrate agar.

Serological test:Positive from 2nd week widle test usually positive.

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