Typhoid fever is caused by S. typhi, a Gram-negative bacterium. World-wide an estimated 17 million cases and 600,000 associated deaths occur annually1. Patients who are infected with HIV are at significantly increased risk of clinical infection with S. typhi2. Evidence of H. pyloriinfection also presents an increase risk of acquiring typhoid fever. 1-5% of patients become chronic carrier harboring S. typhiin the gallbladder.
The clinical diagnosis of typhoid fever depends on the isolation of S. typhifrom blood, bone marrow or a specific anatomic lesion. In the facilities that can not afford to perform this complicated and time-consuming procedure, Filix-Widal test is used to facilitate the diagnosis. However, many limitations lead to difficulties in the interpretation of the Widal test3,4.
In contrast, the Typhoid Ab Rapid Test is a simple and rapid laboratory test. The test simultaneously detects and differentiates the IgG and the IgM antibodies to S. typhispecific antigen5 thus to aid in the determination of current or previous exposure to the S. typhi.
The Typhoid Ab Rapid Test is a lateral flow chromatographic immunoassay. The test cassette consists of: 1) a burgundy colored conjugate pad containing recombinant S. typhoidH antigen and O antigen conjugated with colloid gold (Typhoid conjugates) and rabbit IgG-gold conjugates, 2) a nitrocellulose membrane strip containing two test bands (T1 and T2 bands) and a control band (C band). The T1 band is pre-coated with monoclonal anti-human IgM for the detection of IgM anti-S. typhi, T2 band is pre-coated with reagents for the detection of IgG anti-S. typhi, and the C band is pre-coated with goat anti rabbit IgG.
When an adequate volume of test specimen is dispensed into the sample well of the cassette, the test specimen migrates by capillary action across the test cassette. Anti-S. typhi IgM if present in the patient specimen will bind to the Typhoid conjugates. The immunocomplex is then captured on the membrane by the pre-coated anti-human IgM antibody, forming a burgundy colored T2 band, indicating a S. typhi IgM positive test result.
Anti-S. typhiIgG if present in the patient specimen will bind to the Typhoid conjugates. The immunocomplex is then captured by the pre-coated reagents on the membrane, forming a burgundy colored T1 band, indicating a S. typhi IgG positive test result.
Absence of any test bands (T1 and T2) suggests a negative result. The test contains an internal control (C band) which should exhibit a burgundy colored band of the immunocomplex of goat anti rabbit IgG/rabbit IgG-gold conjugate regardless of the color development on any of the test bands. Otherwise, the test result is invalid and the specimen must be retested with another device.
Reagents And Materials Provided
1. Each foil pouch contains with three items inside
a. One cassette device.
b. One plastic dropper.
c. One desiccant.
2. Sample Diluent
3. One package insert (instruction for use).
Materials Required But Not Supplied
MATERIALS MAY BE REQUIRED AND NOT PROVIDED
1. Positive Control
2. Negative Control
MATERIALS REQUIRED BUT NOT PROVIDED
1. Clock or Timer
Specimen Collection And Preparation
Consider any materials of human origin as infectious and handle them using standard biosafety procedures.
1. Collect blood specimen into a lavender, blue or green top collection tube (containing EDTA, citrate or heparin, respectively in Vacutainer®) by veinpuncture.
2. Separate the plasma by centrifugation.
3. Carefully withdraw the plasma into new pre-labeled tube.
1. Collect blood specimen into a red top collection tube (containing no anticoagulants in Vacutainer®) by veinpuncture.
2. Allow the blood to clot.
3. Separate the serum by centrifugation.
4. Carefully withdraw the serum into a new pre-labeled tube.
Test specimens as soon as possible after collecting. Store specimens at 2°C-8°C if not tested immediately.
Store specimens at 2°C-8°C up to 5 days. The specimens should be frozen at -20°C for longer storage.
Avoid multiple freeze-thaw cycles. Prior to testing, bring frozen specimens to room temperature slowly and mix gently. Specimens containing visible particulate matter should be clarified by centrifugation before testing. Do not use samples demonstrating gross lipemia, gross hemolysis or turbidity in order to avoid interference on result interpretation.
All reagents are ready to use as supplied. Store unused test devices unopened at 2°C-30°C. The positive and negative controls should be kept at 2°C-8°C. If stored at 2°C-8°C, ensure that the test device is brought to room temperature before opening. The test device is stable through the expiration date printed on the sealed pouch. Do not freeze the kit or expose the kit over 30°C.
Step 1: Bring the specimen and test components to room temperature if refrigerated or frozen. Mix the specimen well prior to assay once thawed.
Step 2: When ready to test, open the pouch at the notch and remove device. Place the test device on a clean, flat surface.
Step 3: Be sure to label the device with specimen’s ID number.
Step 4: Fill the pipette dropper with the specimen.
Holding the dropper vertically, dispense 1 drop (about 30-45 µL) of specimen into the sample well making sure that there are no air bubbles.
Then add 1 drop (about 35-50 µL) of Sample Diluent immediately.
Step 5: Set up timer.
Step 6: Results can be read in 15 minutes. Positive results can be visible in as short as 1 minute.
##Don’t read result after 15 minutes. To avoid confusion, discard the test device after interpreting the result. ##
Interpretation of Results
1: In addition to the presence of C band, if only T1 band is developed, the test indicates for the presence of anti-S. typhi IgG in the specimen. The result is IgG positive.
2: In addition to the presence of C band, if only T2 band is developed, the test indicates for the presence of anti-S. typhiIgM in the specimen. The result is IgM positive.
3: In addition to the presence of C band, both T1 and T2 bands are developed, the test indicates for the presence of anti-S. typhiIgG and IgM in the specimen. The result is both IgG and IgM positive.
##*NOTE:## Samples with positive results should be confirmed with alternative testing method(s) and clinical findings before a positive determination is made.
##NEGATIVE RESULT:## If only the C band is present, the absence of any burgundy color in the both test bands (T1 and T2) indicates that no antiS. typhi antibody is detected in the specimen. The result is negative.
##INVALID RESULT:## If no C band is developed, the assay is invalid regardless of any burgundy color in the test bands. Repeat the assay with a new device.
1. ##Internal Control:## This test contains a built-in control feature, the C band. The C line develops after adding specimen and sample diluent. Otherwise, review the whole procedure and repeat test with a new device.
2. ##External Control:## Good Laboratory Practice recommends using the external controls, positive and negative (provided upon request), to assure the proper performing of the assay, in particularly, under the following circumstances:
a. New operator uses the kit, prior to performing testing of specimens.
b. A new lot of test kit is used.
c. A new shipment of kits is used.
d. The temperature used during storage of the kit fall outside of 2°C -30°C.
e. The temperature of the test area falls outside of 15°C -30°C.
##1. Clinical Performance For IgM Test##
A total of 334 samples from susceptible subjects were tested by the Typhoid Ab Rapid Test and by a commercial S. typhi IgM EIA. Comparison for all subjects is showed in the following table. Relative Sensitivity: 91%, Relative Specificity: 99.3%, Overall Agreement: 98.5%
##2. Clinical Performance For IgG Test##
A total of 314 samples from susceptible subjects were tested by the Typhoid Ab Rapid Test and by a commercial S. typhi IgG EIA kit. Comparison for all subjects is showed in the following table. Relative Sensitivity: 92.9% , Relative Specificity: 99.3%, Overall Agreement: 99.0%
• For professional in vitro diagnostic use only.
• Do not use after expiration date indicated on the package. Do not use the test if its foil pouch is damaged. Do not reuse tests.
• This kit contains products of animal origin. Certified knowledge of the origin and/or sanitary state of the animals does not totally guarantee the absence of transmissible pathogenic agents. It is therefore, recommended that these products be treated as potentially infectious, and handled observing the usual safety precautions (do not ingest or inhale).
• Avoid cross-contamination of specimens by using a new specimen collection container for each specimen obtained.
• Read the entire procedure carefully prior to performing any tests.
• Do not eat, drink or smoke in the area where the specimens and kits are handled. Handle all specimens as if they contain infectious agents. Observe established precautions against microbiological hazards throughout the procedure and follow the standard procedures for proper disposal of specimens. Wear protective clothing such as laboratory coats, disposable gloves and eye protection when specimens are assayed.
• Buffered Saline contains sodium azide which may react with lead or copper plumbing to form potentially explosive metal azides. When disposing of buffered saline or extracted samples, always flush with copious quantities of water to prevent azide build up.
• Do not interchange or mix reagents from different lots.
• Humidity and temperature can adversely affect results.
• The used testing materials should be discarded in accordance with local, state and/or federal regulations.
1. The Assay Procedure and the Test Result Interpretation must be closely when testing the presence of antibodies to S. typhi in serum or plasma from individual subjects. Failure to follow the procedure may give inaccurate results.
2. The Typhoid Ab Rapid Test is limited to the qualitative detection of antibodies to S. typhi in human serum or plasma. The intensity of the test band does not have linear correlation with the antibody titer in the specimen.
3. The Typhoid Ab Rapid Test also detects para-typhi antibodies.
4. A negative result for an individual subject indicates absence of detectable anti-S. typhi antibodies. However, a negative test result does not preclude the possibility of exposure to S. typhi.
5. A negative result can occur if the quantity of anti-S. typhi antibodies present in the specimen is below the detection limit of the assay, or the antibodies that are detected are not present during the stage of disease in which a sample is collected.
6. If the symptom persists, while the result from Typhoid Ab Rapid Test is negative or nonreactive result, it is recommended to re-sample the patient few days late or test with an alternative test method, such as bacterial culture method.
7. Some specimens containing unusually high titer of heterophile antibodies or rheumatoid factor may affect expected results.
8. The results obtained with this test should only be interpreted in conjunction with other diagnostic procedures and clinical findings.
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2. Gotuzzo E, Frisancho O, Sanchez J, Liendo G, Carillo C, Black RE, Morris JG. Association between the acquired immunodeficiency syndrome and infection with Salmonella typhi or Salmonella paratyphi in an endemic typhoid area. Archives of Internal Medicine 1991; 151: 381-2
3. Clegg A, Passey M, Omena MK, et al. Re-evaluation of the Widal agglutination test in response to the changing pattern of typhoid fever in the highlands of Papua New Guinea. Acta Tropica 1994;57:255-63
4. Pang T. False positive Widal test in nontyphoid Salmonella infection. Southeast Asian Journal of Tropical Medicine and Public Health 1989; 20: 163-4
5. Ismail A, Hai OK, Kader ZA. Demonstration of an antigenic protein specific for Salmonella typhi. Biochem Biophys Res Commun.1991;181(1):301-5re denude and Japanese encephalitis co-circulate. Am. J. Trap. Med.
Hygiene. 1989: 40: 418-427
6. Anonymous. Dengue hemorrhagic
fever: diagnosis, treatment, prevention and control. 2nd ed. Geneva:
World Health Organization, 1997