Widal Test Flashcards
Typhoid fever
Causative agent:
Salmonella enterica serotype typhi
• Paratyphoid fever
• Causative agent:
Salmonella enterica serotype paratyphi
CAUSATIVE AGENT
ENTERIC FEVER
Family:
Enterobacteriaceae
Characteristics
Gram stain…
Motility…
Oxidase…
TSI:…
LF?..
Agar…
Gram negative bacilli
Motile
(-)
K/A, G (-), H2S (+)
Non-lactose
Colorless fermenter/ colonies on MacConkey agar
MODE OF TRANSMISSION
TYPHOID FEVER
Through food, drinks, and water that have been contaminated by sewage
Through food that has been rinsed
in contaminated water and then eaten
Through food that has been touched by a person who did not wash their hands after using the bathroom or changing a diaper
Fecal-oral route
SIGNS AND SYMPTOMS
TYPHOID FEVER
•______ is common.
• People can have other symptoms, including: WSHCCL
• Some people get a….
Fever
• Weakness
• Stomach pain invade vall westine
• Headache
• Constipation or diarrhea
• Cough
• Loss of appetite
rash with flat, rose-colored spots.
_____less severe
Paratyphoid
Antigens of Salmonella typhi
H
O
Vi
Antigens of paratyphi
O
H
•
Flagellin/Flagellar antigen
•
Cell wall/Somatic antigen
•
Capsular polysaccharide
Important for immune evasion and intracellular invasion
H antigen
O antigen
Vi antigen
Salmonella paratyphi
H antigen
O antigen
Flagellin/Flagellar antigen
Cell wall/Somatic antigen
Paratyphi
Additional antigens:
• S. paratyphi A:
• S. paratyphi B:
A
B
• A serological test used for over a century to help diagnose typhoid fever.
WIDAL TEST
WIDAL TEST
• It was developed in 1896 by….
Georges-Fernand-Isidor Widal
Widest test
• The test works by detecting antibodies in patient’s serum that are specific to the antigens of_______, the bacterium that causes typhoid fever.
Salmonella typhi
PRINCIPLE
WIDAL TEST
• Direct agglutination
The test uses suspensions of killed Salmonella typhi bacteria treated to retain specific antigens, namely the O (somatic) and H (flagellar) antigens.
Antigens
Direct agglutination
• Antigens
The test uses suspensions of killed Salmonella typhi bacteria treated to retain specific antigens, namely the
O (somatic) antigens
H (flagellar) antigens
• Serum
• A sample of the patient’s blood is taken, and the serum, the liquid portion containing____ against O and H antigens, is separated.
antibodies
• Observation and Interpretation
Presence of agglutination:
Absence of agglutination:
Positive
Negative
INTRODUCTION
WIDAL TEST
_______ (type of test)
• The correlation of test results with typical signs, symptoms, and patient’s history should be taken into account before arriving at the final diagnosis.
• The test is standardized in such a way that they can be used for____ or ____ technique
Screening test
slide or tube technique
Widal Test
• An undiluted serum is used in___ test.
• It is simple, rapid, and convenient screening test.
slide
Widal test
• In doubtful cases, it is recommended to perform the_____ technique for obtaining a conclusive result.
• A marked rise in the titer to one serotype (______) suggests infection.
• Diagnostically, a rising antibody titer of at least_____ (two tube difference) is considered more significant than a single test.
tube
above 1:80
four-fold
WIDAL TEST
ADVANTAGES
SIM
• Relatively simple to perform
• Relatively inexpensive
• Rapid and useful for monitoring the extent of an outbreak
WIDAL TEST
DISADVANTAGES
NLILDN
• Non-specific, Cross-reactivity
• Lack of standardization
• Influence of prior exposure
• Limited diagnostic value of a single
test
• Difficulty in interpreting results
• Not as accurate as bacterial culture
Widal test
False negatives: (3)
First week of infection
hyperproteinemia
immune deficiencies
Widal test kit containing Salmonella antigens
O-antigen of Salmonella Typhi
H-antigen of Salmonella Typhi
AH-antigen of Salmonella Paratyphi A
BH-antigen of Salmonella Paratyphi B
Color
O-antigen of Salmonella Typhi
Blue
Color
H-antigen of Salmonella Typhi
Red
Color
AH-antigen of Salmonella Paratyphi A
Yellow
Color
BH-antigen of Salmonella Paratyphi B
Green
TEST KIT: CONTROLS
WIDAL TEST
POSITIVE CONTROL
Contains ready to use standardized ____ antiserum with ______ having specific reactivity towards:
• S. typhi O and H antigens
• S. paratyphi AH and BH antigens
• S. paratyphi AO and BO antigens
• S. paratyphi CO and CH antigens
• Useful in the validation of the performance of Widal reagents.
goat antiserum with polyspecific antibodies
TEST KIT: CONTROLS
WIDAL TEST
Contains no antibodies against
the specific bacteria.
NEGATIVE CONTROL
TEST KIT: CONTROLS WIDAL TEST
• Notes:
• A ______ and ______should be run with each test.
• If the reagent fails to agglutinate with the positive control, or does agglutinate with the negative control, it should be_____.
positive and negative control
discarded
TEST KIT: REAGENT WIDAL TEST
The kit contains antigen suspensions of_____ and were stained to
enhance the reading of agglutination tests.
The blue stained antigens are specific to the_______, while the red stained antigens are specific to the_______.
killed bacteria
somatic antigens (O-Ag)
flagellar antigens (H-Ag)
TEST KIT: REAGENT WIDAL TEST
• Types of Antigens used in Widal Test:
________: the thermolabile flagellar antigen
_______: thermostable somatic antigen
“H” (Hauch) antigen
“O” (Ohne) antigen
SAMPLE
WIDAL TEST
No special preparation of the patient is needed : Clean and dry glassware free from detergents must be used for sample collection.
• ______sample is preferred.
• Do not use hemolyzed samples, turbid,
contaminated or inactivated serum.
• In case of delay the sample should be stored at _____and away from____
• Test should be performed within _____of sample collection.
Fresh serum
2-8°C ; direct sunlight
24 hrs.
PROCEDURE
WIDAL TEST
• Storage and Stability
• All reagents are stable till expiry date as mentioned on the label of the kit, only when maintained at 2-8°C away from sunlight.
Do not_____.
Precautions before testing
Bring all reagents and samples to
______before use
Shake all the antigens thoroughly
before use.
freeze
room temperature
PROCEDURE
RAPID SLIDE TEST (SCREENING)
1. Clean the glass slide provided in the kit and wipe.
- Place one drop of undiluted serum to be tested in each of the first four circles (1-4).
- Add one drop of antigen ___,___,____,____in circles 1, 2, 3, 4 respectively.
- Mix the contents of each circle with separate stick and spread to fill the entire circle area.
- Rock the slide for ____and observe PC” for agglutination.
- If agglutination is visible within one minute then proceed for_____
O, H, A(H) and B(H)
one minute
quantitative estimation.
PROCEDURE
RAPID SLIDE TEST (SCREENING)
INTERPRETATION
• Valid result
Agglutination with____ control
No agglutination with____ control.
• Negative result
No agglutination up to _____indicates the absence of corresponding antibodies.
• Positive result
Agglutination ______indicates presence of corresponding antibodies.
Proceed for ______for determination of antibody titer.
• Do not observe result after_____
positive; negative
one minute
within one minute
semi-quantitative slide or tube technique
one minute
is the highest dilution observed in rapid slide screening test which gives visible agglutination.
Titer
PROCEDURE
QUANTITATIVE SLIDE TEST
• To each of the above circles, add one drop of the appropriate antigen, which gives agglutination in the screening slide test
• Mix the contents of each circle separately and spread it in the entire circle.
• Rotate the slide by hand or on a mechanical rotator at 100 r.p.m. for 1
minute.
• Observe for agglutination in any of the circles
• A diagnostic titer of_____ suggests positive reaction.
1:80
• NOTE:
• The lowest volume of serum which shows clear agglutination indicates the cut-off level of the positive test and the corresponding antibody titer as seen on the table.
In non vaccinated persons the titer as high as 1: 80 between _____day of fever is of diagnostic value and the same titer increases gradually during subsequent period.
7th or 10th
In vaccinated persons the question of anamnestic response should always be borne in mind and ‘____’ titer should not be taken into account for the purpose of diagnosis unless there is a rising titer of ‘H’ in subsequent period.
H
• The Widal test has a very low specificity, less sensitive, confusing and difficult to interpret for the diagnosis of typhoid fever, because cross-agglutinating antibodies remaining from past infections with related salmonella
serotypes give false-positive results.
True
• While more specific tests are now available like_____\, but the Widal test is still considered useful in diagnosing typhoid fever in developing countries because of its low cost, and it remains in use in many areas throughout the world.
Typhidot Tests
• While more specific tests are now available like_____\, but the Widal test is still considered useful in diagnosing typhoid fever in developing countries because of its low cost, and it remains in use in many areas throughout the world.
Typhidot Tests
