Widal test

Question 1

gold standard for detection of salmonella

Answer 1

blood culture for isolation
typhidot qualitative testing

Question 2

widal test is to diagnose enteric or typhoid fever that is caused by what micoorganisms?

Answer 2

• S. typhi
• S. paratyphi A, B, and C

Question 3

principle of widal test

Answer 3

agglutination (clumps)

Question 4

composed to proteins. its antibody formation is rapid and sustained, highly immunogenic and its antibody levels persists for a longer period

heat — and —

Answer 4

Flagellar antigen
H antigen

heat labile and sensitive

Question 5

composed of polysaccharide, is heat — and alcohol —. its antibody formation is rapid but only on an early phase, — immunogenic, and its antibody levels falls off quickly

Answer 5

Somatic “O” antigen
heat stable and alcohol resistant
less immunogenic

Question 6

it is the surface polysaccharide envelope covering the O antigen. this antigen is expressed only on a few serotypes and renders the Bacilli inagglutinable with O anti-serum. the name is believed to be related in virulence

Answer 6

Surface Vi antigen

Question 7

what is being detected by the widal test?

Answer 7

O and H antigen

Question 8

widal uses — and was discovered by — in 1896

Answer 8

uses direct agglutination
discovered by Fernand Widal

Question 9

enumerate the clinical manifestations

Answer 9

• chest congestion
• constipation
• diarrhea
• gastroenteritis
• headache
• body malaise
• high temperature
• loss of apetite
• stomach pain

Question 10

mode of transmission

Answer 10

• ingestion of contaminated food or water
• person to person
• fecal-oral route
• carriers from food handlers

Question 11

enumerate the procedures that can be used to detect typhoid infections

Answer 11

• widal test (rapid slide)
• widal test (tube agglutination)
• typhoid test (IgG or IgM rapid test)
• ELISA
• electrochemiluminiscent immunoassay
• PCR

Question 12

— stained organisms are specific to somatic (O) antigen while the — stained organisms are specific to flagella (H) antigen

Answer 12

blue - O antigen
red - H antigen

Question 13

widal kit inclusions

Answer 13

• antigen suspension
• positive control vial
• negative control vial
• package insert
• white glass slide
• stirring sticks

Question 14

positive control contains ready to use — with polyspecifc antibodies having specific reactivity towards O and H antigens, useful in the validation of the performance of widal reagents

Answer 14

standardized goat antiserum with polyspecific antibodies

Question 16

this control does not contain antibodies against the specific bacteria

Answer 16

widal negative control

Question 17

why widal is difficult to interpret for diagnosis of typhoid fever?

Answer 17

because cross-agglutinating antibodies remaining from the past infection with related salmonella giving FALSE POSITIVE results

Question 18

advantages of widal

Answer 18

cheap
accessible
simple

Question 19

enumerate the causes of false positives

Answer 19

• previous immunization with salmonella antigen
• cross-reaction with non-typhoid salmonella
• variability and poor standardized commercial antigen preparation kit
• infection with malaria
• other enterobacteriaceae with the same endotoxins or lipopolysaccharides