Widal Test Flashcards by Kyra Catedral

Typhoid fever
Causative agent:

Salmonella enterica serotype typhi

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• Paratyphoid fever
• Causative agent:

Salmonella enterica serotype paratyphi

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CAUSATIVE AGENT
ENTERIC FEVER
Family:

Enterobacteriaceae

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Characteristics
Gram stain…
Motility…
Oxidase…
TSI:…
LF?..
Agar…

Gram negative bacilli

Motile

(-)

K/A, G (-), H2S (+)

Non-lactose

Colorless fermenter/ colonies on MacConkey agar

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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

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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.

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_____less severe

Paratyphoid

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Antigens of Salmonella typhi

H
O
Vi

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Antigens of paratyphi

O
H

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•
Flagellin/Flagellar antigen
•
Cell wall/Somatic antigen
•
Capsular polysaccharide
Important for immune evasion and intracellular invasion

H antigen

O antigen

Vi antigen

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Salmonella paratyphi

H antigen

O antigen

Flagellin/Flagellar antigen

Cell wall/Somatic antigen

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Paratyphi

Additional antigens:
• S. paratyphi A:
• S. paratyphi B:

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• A serological test used for over a century to help diagnose typhoid fever.

WIDAL TEST

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WIDAL TEST

• It was developed in 1896 by….

Georges-Fernand-Isidor Widal

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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

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PRINCIPLE
WIDAL TEST

• Direct agglutination

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The test uses suspensions of killed Salmonella typhi bacteria treated to retain specific antigens, namely the O (somatic) and H (flagellar) antigens.

Antigens

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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

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• 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

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• 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. 2. Place one drop of undiluted serum to be tested in each of the first four circles (1-4). 3. Add one drop of antigen ___,___,____,____in circles 1, 2, 3, 4 respectively. 4. Mix the contents of each circle with separate stick and spread to fill the entire circle area. 5. Rock the slide for ____and observe PC" for agglutination. 6. 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.

• 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